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Physiological stress response, reflex impairment, and survival of five sympatric shark species following experimental capture and release
Abstract
In many fisheries, some component of the catch is usually released. Quantifying the
effects of capture and release on fish survival is critical for determining which practices are sustainable,
particularly for threatened species. Using a standardized fishing technique, we studied
sublethal (blood physiology and reflex impairment assessment) and lethal (post-release mortality
with satellite tags) outcomes of fishing stress on 5 species of coastal sharks (great hammerhead,
bull, blacktip, lemon, and tiger). Species-specific differences were detected in whole blood
lactate, partial pressure of carbon dioxide, and pH values, with lactate emerging as the sole
parameter to be significantly affected by increasing hooking duration and shark size. Species-specific
differences in reflex impairment were also found; however, we did not detect any significant
relationships between reflex impairment and hooking duration. Taken together, we ranked each
species according to degree of stress response, from most to least disturbed, as follows: hammerhead
shark > blacktip shark > bull shark > lemon shark > tiger shark. Satellite tagging data
revealed that nearly 100% of all tracked tiger sharks reported for at least 4 wk after release, which
was significantly higher than bull (74.1%) and great hammerhead (53.6%) sharks. We discuss
which mechanisms may lead to species-specific differences in sensitivity to fishing and suggest
that observed variation in responses may be influenced by ecological and evolutionary phenomena.
Moreover, our results show that certain species (i.e. hammerhead sharks in this study) are
inherently vulnerable to capture stress and mortality resulting from fisheries interactions and
should receive additional attention in future conservation strategies.
... Although the practice of catch-and-release fishing is advocated in recreational fisheries, questions remain about levels of post-release mortality [8,9] as well as more cryptic sub-lethal effects on growth and fitness due to stress, injuries, and increased susceptibility to predation [9][10][11][12]. While some studies have examined the physiological stress caused by catch-and-release fishing on sharks using other fishing techniques (e.g., longlining or drumlining) [13][14][15], there have been comparatively fewer studies evaluating the physiological stress response of sharks to common recreational angling gears or methods [16,17]. ...
... With a relatively high cost of movement and low metabolic rate, nurse sharks are energetically suited for, and perhaps dependent on, a minimally active lifestyle [30] and may experience negative physiological consequences if forced to actively 'fight' on a line. Identification of these angling-related consequences and their impact is essential for the development of best management and conservation practices for this species as they are often captured by shore-based recreational anglers [26] and they are commonly perceived as a robust shark species by both scientists [13] and recreational anglers in South Florida [33]. ...
... The physiological stress response of juvenile nurse sharks to recreational angling species [13,14], their strong site fidelity increases the risk of repeated captures and subsequent physiological responses. This potential chronic stress has been shown in other species to suppress growth, reduce reproductive success, and limit foraging energy, and can lead to increased predation risk and reduced survival [48,49]. ...
Nurse sharks (Ginglymostoma cirratum), especially juveniles, are often encountered by near-shore and shore-based recreational anglers and are suggested to exhibit minimal behavioral and physiological responses to capture, largely based on studies of adults using commercial or scientific fishing methods. To quantify the sub-lethal effects of recreational angling on juvenile nurse sharks, 27 individuals (across 31 angling events) were caught using hook-and-line fishing methods. Over a 30-min period, 4 blood samples were taken with variable time intervals between sampling (i.e., randomized ordering of an interval of 5, 10, and 15 min between each sampling event). Lactate increased by 611% (6.7 ± 2.17 mmol/L) on average over the 30-min fight, and significant relationships were identified between lactate and blood draw number, fight time, and temperature, with large effect sizes. Significant relationships were also detected between blood draw number, glucose, and hematocrit, while osmolality was only affected by fishing site. These results suggest juvenile nurse sharks may exhibit a greater physiological stress response when exposed to recreational angling than adults captured with other fishing methods.
... The increase in lactate between the time points is consistent with other elasmobranch physiology studies, which have demonstrated that, during excessive muscle exertion, hypoventilation, or physiological stress, lactate increases [11,12,[37][38][39][40]. This is further supported by a significant decrease in the pH between the time points. ...
... In its normal response to reduce pH changes, the body uses bicarbonate to buffer the blood for pH recovery; thus, a homeostatic shift of HCO 3 will occur and result, in part, in a concomitant change in the BE (the total of all the bases in the blood) as a response [41]. The oxygen saturation in general in point-of-care blood gas units is considered to be inaccurate due to difficulty in obtaining an arterial versus venous sample, and it is often highly variable; thus, the results are difficult to interpret [38]. ...
... These results are similar to those of other studies, which have demonstrated the same pattern in spiny dogfish, Squalus suckleyi [20], and juvenile blacktip reef sharks, Carcharhinus melanopterus [8]. T. semifasciata demonstrated an overall low stress response compared to other species (e.g., great hammerheads, Sphyrna mokarran) [38,46]. Lactate is significantly correlated with 1α-OHB, as well as corticosterone. ...
Background: Leopard sharks (Triakis semifasciata) are abundant, coastal, eastern Pacific, mesopredatory sharks and are frequently managed in aquariums and zoos. Medical examinations are a routine part of good husbandry practices, but the handling protocols vary greatly between facilities. In this study, we compared the physiological stress responses of T. semifasciata associated with manual restraint and sedated handling under parallel holding and handling procedures in a 10 min interval. Methods: Blood was collected and analyzed for the hematocrit (Hct), lactate, glucose, beta-hydroxybutyrate (β-HB), pH, blood gasses, 1α-hydroxycorticosterone (1α-OHB), and corticosterone (B). Results: Overall, a minimal physiological stress response was observed in both groups. However, statistically significant increases in the PCO2, β-HB and lactate occurred, while the pHTC, SO2, and BE decreased over time in the manual-restraint group. In the sedated group, the B, PCO2, and lactate increased while the pHTC, SO2, and base excess (BE) decreased over time. When comparing treatments, the sedated group had a higher B and PCO2 TC and a lower pHTC, BE, and SO2 than the manual-restraint group at the second time point. Conclusions: This study indicates that manual restraint is comparable to the described sedation in T. semifasciata for minimally invasive procedures. The overall results show that this species had low physiological stress responses to both methods.
... As such responses are an innate aspect of an animals' physiology, a failure to elicit a response can be considered as a sign of stress (Davis & Ottmar, 2006). These actions or responses commonly include, but are not restricted to normal posture, righting, dorsal fin erection, body flex, escape behaviour, operculum and mouth closure, and eye rolls when the body is rotated in bony fishes, shooting of the nictitating membrane in Elasmobranchs (Campbell et al., 2010;Davis, 2010;Gallagher et al., 2014). They can be quantified based on their presence or absence after stimulating the fish with multiple stressors either individually, or as a combination (Davis, 2010). ...
... These factors make reflex impairment observation a reliable method for measuring stress in real time with ease. Several studies in the past have used this in conjunction with other techniques to estimate the post-release, discarded fish, escapees, and delayed mortalities in fisheries for the teleosts (Davis, 2005;Humborstad, 2023;Raby et al., 2012;Stachura et al., 2012), elasmobranchs (Danylchuk et al., 2014;Gallagher et al., 2014), and crustaceans (Stoner et al., 2008), as well as on a range of fishing methods such as catch-and-release fishing (Campbell et al., 2010), long lines (Stachura et al., 2012), angling , beach seines (Raby et al., 2012), purse seines , and trawl nets (Parker et al., 2003;Ryer et al., 2004). ...
... Among the physiological alterations triggered by stress, notable ones include an increase in circulating lactate concentrations, ionic imbalances and the mobilization of energy reserves (Pickering & Pottinger, 1995;Wendelaar Bonga, 1997;Schreck & Tort, 2016). In the case of elasmobranchs, responses to capture stress are commonly assessed through serum/plasma markers, such as lactate and glucose (Hoffmayer & Parsons, 2001;Gallagher et al., 2014;Fuller et al., 2020;Weber et al., 2021), while ions (e.g., chloride, sodium, potassium, magnesium and phosphorus) and urea are less frequently examined (Ferreira, Field, & Tuttle, 2010;Brooks et al., 2012;Heard et al., 2014;Wosnick et al., 2017). To gain a deeper understanding of the pathways and compensatory mechanisms activated by stressors, it is crucial to comprehend how these chosen markers will behave. ...
... Lactate stands as one of the most reliable physiological stress indicators for elasmobranchs, extensively applied in research encompassing diverse species and capture methods (Kneebone et al., 2013;Hyatt, Anderson, & O'Donnell, 2016;Martins, Walker & Reina, 2018). Its efficacy hinges on the biochemical process governing its release into the bloodstream, modulated by the activation of anaerobic metabolism when oxygenation becomes insufficient, a condition frequently encountered by animals during the fight or flight response (Wood, 1991;Gallagher et al., 2014). In the context of monitoring guitarfish for recovery, the significance of lactate clearance becomes evident as it prevents systemic lactic acidosis, which can potentially lead to respiratory and cardiac failure as well as tissue necrosis (Hyatt, Anderson, & O'Donnell, 2016;Whitney et al., 2021). ...
Understanding how animals respond to stressors is critical for effective conservation. The present study aimed to evaluate the physiological recovery of the Shortnose Guitarfish, Zapteryx brevirostris after being incidentally captured by artisanal fleets and compared it to guitarfish with delayed mortality. Moreover, the study aimed to test the efficiency of a rehabilitation protocol for the species. To this end, individuals landed alive were transported to the rehabilitation facilities and kept in tanks under monitoring for 3 days. Physiological markers indicative of allostatic overload (i.e., lactate and phosphorus) and energy metabolism (i.e., glucose and β‐hydroxybutyrate) were assessed in the serum of the studied guitarfish: right after gillnet capture (i.e., post‐capture) and on rehabilitation (i.e., pre‐monitoring, post‐monitoring, as well as guitarfish that deceased during monitoring – post‐mortem). Results showed that the transportation and additional handling employed in the rehabilitation protocol did not increase the stress response, pointing to its potential efficacy in recovering debilitated, incidentally caught guitarfish before release. As for recovery success of monitored guitarfish, lactic acidosis was fully reverted after a 3‐day rest period, as was allostatic overload. The same was not observed in recovery failure. Correlation tests revealed key relationships between physiological markers, shedding light on how physiological pathways help guitarfish cope with capture and handling stress. This study highlights the valuable application of conservation physiology principles to fisheries management of this endemic and threatened guitarfish species.
... However, this may not always be the case, and, generally the survival of fish post-release has been shown to vary according to environmental conditions (Gingerich et al., 2007), and angling methods (see Bartholomew andBohnsack, 2005 andBrownscombe et al., 2017 for general reviews). Survival also appears to be species specific (Musyl and Gilman, 2019), with some species, such as the great hammerhead shark (Sphyrna mokarran), exhibiting low post-release survivorship (PRS, e.g. in Gallagher et al., 2014 only 57% of 28 hammerhead sharks were considered to survive, whereas 100% of 28 tiger sharks, Galeocerdo cuvier, survived). The C&R angling sector has therefore developed an array of "best practices" to increase PRS (e.g. ...
... Direct, statistically significant, evidence of a negative effect of prolonged fight time on PRS is, however, lacking. Instead, research has suggested that longer fight (in recreational settings) or capture times (in commercial settings) may not always translate into higher stress levels (Gallagher et al., 2014(Gallagher et al., , 2019Musyl et al., 2015;Tate et al., 2019;Shea et al., 2022). This response is likely to be species-specific (Jerome et al., 2018) due to differences in exertion between species (Gallagher et al., 2017b). ...
In recent decades, the abundance of sharks in the world's oceans has decreased due to overexploitation by commercial fisheries. Over this same period, sharks have been increasingly targeted for sport by recreational anglers. "Catch-and-release" (C&R) angling, where sharks are released alive after capture, has been proposed, and in some situations, mandated as a conservation measure in recreational fisheries. In C&R fisheries, anglers are encouraged to follow best practices, each with the goal of maximising post-release survivorship (PRS) of angled fish. Here for sharks, we review C&R global best practices and the science underpinning them. Despite shark C&R fishing being practiced globally, peer-reviewed research into post-release survivorship is limited to just twelve studies for eight species (Lamniformes, n = 3; Carcharhiniformes, n = 5). PRS in studies ranged from 56% to 100%. Identifying causes for decreased PRS (i.e. mortality) was challenging for studies due to low sample sizes. Of the factors investigated, candidate best practices included: (1) using non-stainless steel circle hooks, (2) not removing sharks from the water, (3) reviving sharks prior to release, and (4) minimising time spent freeing the shark by removing the hook or cutting the line. With the conservation status of many sharks declining, more research is needed to strengthen the scientific basis for these practices to ensure that PRS in C&R is maximised.
... Under restrained conditions, AST, NH 3 , CPK, and BUN values were significantly elevated. Numerous studies have examined stress in elasmobranchs, especially in sharks, in relation to catch-and-release practices in fisheries and leisure activities (Moyes et al. 2006;Mandelman and Skomal 2009;Gallagher et al. 2014a). Based on these studies, AST and CPK levels likely increased due to muscle damage caused by restraint (Stoskopf 1993;Otway et al. 2011;Wells et al. 1986;Stoskopf 2010;Harms et al. 2002;Cain et al. 2004;Cliff and Thurman 1984;Manire et al. 2001). ...
This study aimed to establish reference intervals for red and white blood cell counts, hematocrit levels, mean corpuscular volume, and 25 key plasma biochemistry parameters in captive and wild whale sharks (Rhincodon typus). Blood samples were collected from the caudal vein (CV) and dorsal cutaneous vein (DCV) of 30 wild sharks caught in fixed nets off the Kochi Prefecture coast, Japan, and from 24 captive sharks between 2007-2023. Samples were obtained from restrained captive and wild sharks as well as unrestrained captive sharks trained for husbandry. Comparative analyses considered three factors: captivity status (wild vs. captive sharks under restraint), blood sampling sites (CV vs. DCV under restraint), and handling methods (DCV sampling under restrained vs. unrestrained conditions). Analysis of captivity status revealed significant differences in 12 of 29 parameters, with triglyceride levels significantly lower in wild sharks, possibly indicating nutritional deficiencies due to their prolonged migrations. Comparisons of blood sampling sites revealed significant differences in 11 parameters, including red and white blood cell counts and hematocrit levels, with most CV-derived parameters being higher than those from the DCV. A strong correlation (r > 0.7) was found between the CV and DCV for 19 parameters, indicating predictive values between these vessels. Additionally, the relationship between RBC, Ht, and MCV indicates that the RBC and MCV results may not be entirely reliable and should therefore be interpreted with caution. In the handling method comparison, eight parameters exhibited significant differences; specifically, aspartate aminotransferase, ammonia, and creatine phosphokinase levels were likely influenced by stress effects, including restraint-induced muscle damage. These findings emphasize the importance of unrestrained blood collection, facilitated through husbandry training, for accurate blood parameter evaluations. Integrating statistical results across the three studied factors allowed for the establishment of reference intervals, means, and medians for whale sharks, contributing to health management in captive sharks and conservation in wild populations. Citation: Ito T, Segawa T. 2025. Hematology and plasma biochemistry in whale sharks (Rhincodon typus): baseline reference intervals based on captivity status, blood sampling sites, and handling methods. Zool Stud 64:01.
... data), indicating that delayed or captivity effects can manifest in the net pen. Complementary techniques like blood chemistry analysis (e.g., Gallagher et al., 2014;Sepulveda et al., 2020) could allow the physiological effects of capture, handling, transport, and holding on white seabass to be better distinguished in the future. ...
White seabass (Atractoscion nobilis) are highly prized on the Pacific coast of North America. Size-based, seasonal, and spatial harvest regulations are in place for this species, leading to the release of live fish in hook-and-line fisheries. To better understand how releases may be affecting the population of this species in the Southern California Bight, 161 white seabass (420–1425 mm in total length [TL]) were captured by hook and line over a 4-year period (2021–2024). Biological, environmental, and fishing data were recorded for each capture event, and fish were subsequently released into a large (630-m3) net pen. The short-term postrelease mortality of white seabass (i.e., within 24 h) was 14.9% overall. When assessed by using logistic regression, the best-supported model of mortality included hooking location and its interaction with fish TL. Model-predicted mortality was generally lower for fish hooked in the lip (0%–67%) than for fish hooked in the oral cavity or deeper (21%–63%), although mortality increased substantially in lip-hooked individuals >1000 mm TL (10%–67%). A small number of white seabass (11 individuals) had signs of barotrauma, with the results of a separate analysis indicating that these fish were significantly larger and captured at deeper sites than those without barotrauma. These findings can help improve fisheries management decision-making for a species that is heavily targeted by hook-and-line fishing.
... However, elasmobranchs have robust stomachs that can even be inverted and pushed through their mouths (Brunnschweiler et al., 2005;Cortés & Gruber, 1990 and ray morphology appears well suited for gastric lavage, species physiology and behaviour must also be considered when assessing its use. For example, it may not be suitable for species that are highly vulnerable to capture and handling stress, such as larger hammerhead sharks (Sphyrnidae) (Gallagher et al., 2014;Jerome et al., 2018). ...
Traditionally, lethal stomach dissection has been used to study the diets of sharks and rays, but conservation and animal welfare concerns necessitate non‐lethal alternatives, such as gastric lavage (stomach or gut flushing). In this study, we summarised gastric lavage studies on elasmobranchs to identify which species/groups it has been effective for, the difficulties encountered and if post‐release survival has been evaluated. Secondly, we used a field study to (1) demonstrate how to perform gastric lavage on juvenile rays, (2) assess its effectiveness and (3) verify post‐release survival using mark‐recapture techniques. Only 23 published studies have used gastric lavage on either sharks or rays, indicating that this technique is still highly underutilised in ecological research. Effectiveness at obtaining stomach contents varied but often exceeded 50%, particularly for rays. Captivity studies provided greater evidence of survival than field studies, and only one field study assessed long‐term survival using tag‐recapture methods. In this field study, gastric lavage was highly effective for young juvenile rays, and recaptures verified survival for various periods after release. More research is needed to adapt gastric lavage across a wider range of species and sizes, especially larger sharks. Furthermore, incorporating approaches to validate survival following non‐lethal handling procedures will be essential to ensure ethical compliance and optimal outcomes for research and conservation.
... These species are frequently targeted and caught as bycatch in pelagic longline and commercial line fisheries (Zeeberg, Corten, and de Graaf 2006;da Silva et al. 2015;Okes and Sant 2019;Thomas et al. 2021), supplying a significant component of the fin trade (Dent and Clarke 2015;Fields et al. 2018;Cardeñosa et al. 2022). In addition to these significant fishing pressures, the mortality rates associated with high capture stress further threaten the survival of these species (Gallagher et al. 2014;Ellis, McCully Phillips, and Poisson 2017). Compounding these issues, these species are often broadly categorized as multiple hammerhead shark species, "Hammerhead sharks nei," or "Unspecified Hammerhead" in catch data (Dicken et al. 2018;Okes and Sant 2019), posing further challenges for conducting species-specific stock assessments ) and accurately monitoring hammerhead shark population trends. ...
... These species are frequently targeted and caught as bycatch in pelagic longline and commercial line fisheries (Zeeberg, Corten, and de Graaf 2006;da Silva et al. 2015;Okes and Sant 2019;Thomas et al. 2021), supplying a significant component of the fin trade (Dent and Clarke 2015;Fields et al. 2018;Cardeñosa et al. 2022). In addition to these significant fishing pressures, the mortality rates associated with high capture stress further threaten the survival of these species (Gallagher et al. 2014;Ellis, McCully Phillips, and Poisson 2017). Compounding these issues, these species are often broadly categorized as multiple hammerhead shark species, "Hammerhead sharks nei," or "Unspecified Hammerhead" in catch data (Dicken et al. 2018;Okes and Sant 2019), posing further challenges for conducting species-specific stock assessments ) and accurately monitoring hammerhead shark population trends. ...
Globally, hammerhead sharks have experienced severe declines owing to continued overexploitation and anthropogenic change. The smooth hammerhead shark Sphyrna zygaena remains understudied compared to other members of the family Sphyrnidae. Despite its vulnerable status, a comprehensive understanding of its genetic landscape remains lacking in many regions worldwide. The present study aimed to conduct a fine‐scale genomic assessment of Sphyrna zygaena within the highly dynamic marine environment of South Africa's coastline, using thousands of single nucleotide polymorphisms (SNPs) derived from restriction site‐associated DNA sequencing (3RAD). A combination of differentiation‐based outlier detection methods and genotype‐environment association (GEA) analysis was employed in Sphyrna zygaena. Subsequent assessments of putatively adaptive loci revealed a distinctive south to east genetic cline. Among these, notable correlations between adaptive variation and sea‐surface dissolved oxygen and salinity were evident. Conversely, analysis of 111,243 neutral SNP markers revealed a lack of regional population differentiation, a finding that remained consistent across various analytical approaches. These results provide evidence for the presence of differential selection pressures within a limited spatial range, despite high gene flow implied by the selectively neutral dataset. This study offers notable insights regarding the potential impacts of genomic variation in response to fluctuating environmental conditions in the circumglobally distributed Sphyrna zygaena.
... The chosen acoustic transmitter model was small (length: 95 mm; diameter: 16 mm; weight in air: 34 g; weight in water: 14.9 g) compared to the size (range 260e360 cm TL, Table 1) of the sharks in this study and maximally~0.01% of the body weight of individuals (range 141.6e259.1 kg, see Heim et al., 2021). The chosen capture method allowed us to enforce a strict bite-torelease time limit of 12 min based on published lactate build-up levels for the study species (Gallagher et al., 2014) and was regularly reassessed and optimized to further minimize the stress experienced by the sharks. ...
Keywords: dynamic Brownian bridge movement model earth mover's distance elasmobranch endangered movement ecology wildlife provisioning By changing the spatiotemporal availability of resources, tourism-related feeding can have potentially detrimental impacts on the movement ecology of animals, thus possibly undermining its own conservation benefits. A lack of baseline data on natural behaviour and the noninclusion of observation data that adequately incorporates the previous experience of animals with tourism-related feeding have generated contradictory results, causing the true impacts of feeding to remain obscure. Further, the relationship between the energy consumption of fed animals and their space use remains unexplored. Here, we coupled passive acoustic telemetry with previously published observation data at a tourism-related feeding site to investigate how direct feeding affects space use and residency patterns of great hammerhead sharks, Sphyrna mokarran, in Bimini, The Bahamas, at various timescales (ranging from days to 8 years). We first constructed movement models for 28 known fed and naïve sharks (i.e. those that were present at the study site but never attended feeding events) to quantify differences in space use and spatial overlap between those groups. We then compared bait uptake of fed sharks with their space use. Fed sharks showed a marked reduction in space use in response to feeding events and an amplification of these impacts over 5 consecutive years. In contrast, naïve shark space use remained unchanged over the same period. The seasonal residency of fed and naïve great hammerheads remained stable across 8 years, with the sharks leaving the study site during the summer of each year. Our study underscores how the intensification of tourism-related direct feeding progressively alters the space use of apex predators across short and long timescales, with enduring effects on fed animals. Our study further highlights the utility of a naïve animal group for assessing feeding impacts in the absence of baseline data.
... Finally, transitions (movements between two different receivers) were calculated as per Williamson et al. 28 and removed if the speed of the transition exceeded 10 times the minimum sustainable swimming speeds of 0.69 m/s for grey reef sharks, resulting in a cut-off speed of 6.9 ms −128, 85 . To reduce any impact of the stress of capture on detected behaviour 86,87 , the first 24 h of data were removed for each individual 88 . ...
Coral reef ecosystems are highly threatened and can be extremely sensitive to the effects of climate change. Multiple shark species rely on coral reefs as important habitat and, as such, play a number of significant ecological roles in these ecosystems. How environmental stress impacts routine, site-attached reef shark behavior, remains relatively unexplored. Here, we combine 8 years of acoustic tracking data (2013-2020) from grey reef sharks resident to the remote coral reefs of the Chagos Archipelago in the Central Indian Ocean, with a satellite-based index of coral reef environmental stress exposure. We show that on average across the region, increased stress on the reefs significantly reduces grey reef shark residency, promoting more diffuse space use and increasing time away from shallow forereefs. Importantly, this impact has a lagged effect for up to 16 months. This may have important physiological and conservation consequences for reef sharks, as well as broader implications for reef ecosystem functioning. As climate change is predicted to increase environmental stress on coral reef ecosystems, understanding how site-attached predators respond to stress will be crucial for forecasting the functional significance of altering predator behavior and the potential impacts on conservation for both reef sharks and coral reefs themselves.
... For use in aquariums or research, those collecting sharks tend to take greater care to minimize risk to captured animals (Jorgensen et al. 2022); therefore, capture scenarios are not always reflective of commercial or even recreational fishing practices. Indeed, researchers often publish best-practice guidelines for minimizing deleterious outcomes of capture (e.g., Horton et al. 2023), and explicitly refer to fishing gear as "scientific" or "experimental" (e.g., Gallagher et al. 2014;Talwar et al. 2020). Despite this, physiological stress and capture related mortality in sharks can depend on capture method. ...
Sharks are collected from the wild as live specimens for display in aquariums and use in research. The methods by which live sharks are captured and transported can be associated with sub-lethal physiological outcomes or even mortality, which requires evaluation to determine optimal collection and transport methods for a given species. The present study evaluated the primary (i.e., endocrine) and secondary (i.e., biochemical) stress responses and mortality in Pacific spiny dogfish (Squalus suckleyi) following capture and subsequent transport between experimental rod-and-reel angling and longline fishing. Dogfish were resilient to transport following capture by either method, exhibiting no at-vessel mortality and 0.03% delayed mortality. Longline captured dogfish exhibited signs of primary (i.e., elevated corticosterone) and secondary (i.e., elevated plasma potassium, osmolality, glucose, and lactate; decreased blood pH) stress responses, whereas dogfish that experienced rod-and-reel capture and transport only exhibited a secondary stress response (i.e., elevated plasma potassium, osmolality, and lactate; decreased blood pH). Together, these data demonstrate that Pacific spiny dogfish are robust to capture and transport using experimental hook-and-line fishing techniques.
... Hemipristis elongata) (Anam and Mostarda 2012) were not landed. This absence might indicate overfishing, as these species often diminish following the capture of larger species like bull sharks and scalloped hammerheads (Gallagher et al. 2014). Alternatively, fishers may have been catching these species but not landing them ashore. ...
Artisanal fisheries in Kenya face substantial challenges, including inadequate enforcement, absence of tailored regulations for elasmobranch conservation and lack of robust data collection systems, hampering our understanding of fisheries and biological aspects of species. To address these challenges, this study examined the species composition, size, weight and number of shark and ray landings in three sites historically known for large catches of elasmobranchs. This research aimed to characterise Kenyan elasmobranchs fishery and exhibit its overlap with key habitats. Our findings are worrying since 79% of the landed fisheries species are categorised as threatened on the IUCN Red List. This includes the Critically Endangered scalloped hammerhead shark (Sphyrna lewini) and white-spotted guitarfish (Rhynchobatus djiddensis), both species frequently caught. Further, 97% of sharks and 46% of rays are landed as neonate and immature individuals. Urgent changes are imperative in national fisheries management to prevent the potential local disappearance of several shark and ray species. We recommend specific conservation measures to reduce the capture of threatened species and juveniles, such as banning the landing of threatened species and establishing minimum size limits. Enforcing fisheries regulations, such as mesh size, and prioritizing the protection of key habitats for the most at-risk species are essential proactive steps.
... Ce taux élevé s'expliquerait par la survenue de réactions de stress comportementales et physiologiques lors de la capture des requins. En effet, les requins-marteaux se voient être fortement affectés par un stress de nature physiologique et physique lors de la capture (Gallagher et al., 2014c). Pour le requin-marteau halicorne, le taux de mortalité à bord et après la remise à l'eau peut atteindre plus de 90 % après la capture (Butcher et al., 2015 ;Coelho et al., 2012 ;Morgan & Burgess, 2007). ...
L'évaluation du statut des populations par la Liste rouge de l'Union Internationale pour la Conservation de la Nature (UICN) indique que les requins constituent l'un des groupes les plus menacés au niveau mondial, principalement en raison de la surpêche sévissant dans les océans du monde entier. La surexploitation des grands prédateurs marins, dont les requins, est fortement répandue dans les océans du monde entier mais l'importance et l'impact des déclins restent mal compris et trop peu connus du grand public. En effet, les requins résident au sommet des réseaux trophiques marins et constituent des espèces clés jouant un rôle essentiel dans la stabilité et l'équilibre des écosystèmes. En éliminant les individus vieux ou malades pour de nombreuses espèces, les requins participent au renforcement du pool génétique des populations et donc au bon état de santé des populations. Les requins-marteaux (Sphyrnidae) présentent des caractéristiques et des comportements spéciaux augmentant ainsi leur vulnérabilité à l'exploitation humaine. En rassemblant les données issues de travaux scientifiques réalisés sur les états et évolutions des populations de Grands requins-marteaux Sphyrna mokarran, requins-marteaux halicorne Sphyrna lewini et requins-marteaux lisse Sphyrna zygaena, les résultats montrent d'importants déclins dans les abondances des différentes populations à l'échelle mondiale dont les principales menaces sont les captures ciblées et accessoires de la pêche. Il semble urgent de mettre en place des méthodes de pêche plus sélectives, des règlementations fortes pour limiter les captures, de créer des zones marines protégées efficaces et d'adopter des approches visant à minimiser la mortalité des espèces étudiées dans le but d'assurer le bon équilibre des écosystèmes marins. Bien que certaines mesures de conservation aient déjà été prises dans le passé, la mise en place d'actions immédiates supplémentaires dans le contexte environnemental présent est essentielle afin d'éviter de nouvelles extinctions.
... An increase in the occurrence of G. cuvier in Isla del Coco does not necessarily reflect a broader population trend but is more likely the result of the species establishing residence on the island due to suitable environmental conditions and foraging opportunities 21 . While fishing pressure remains high outside Isla del Coco, a species with relatively high intrinsic rate of increase and post-release survival like G. cuvier may have some advantages over other elasmobranch species 51 . In addition, based on recent shark landing data (2015-2021) for the Pacific of Costa Rica, G. cuvier does not appeared to be a common bycatch species, suggesting there is currently minimal interaction with pelagic fisheries 52 . ...
No-take marine protected areas (MPAs) can mitigate the effects of overfishing, climate change and habitat degradation, which are leading causes of an unprecedented global biodiversity crisis. However, assessing the effectiveness of MPAs, especially in remote oceanic islands, can be logistically challenging and often restricted to relatively shallow and accessible environments. Here, we used a long-term dataset (2010–2019) collected by the DeepSee submersible of the Undersea Hunter Group that operates in Isla del Coco National Park, Costa Rica, to (1) determine the frequency of occurrence of elasmobranch species at two depth intervals (50–100 m; 300–400 m), and (2) investigate temporal trends in the occurrence of common elasmobranch species between 2010 and 2019, as well as potential drivers of the observed changes. Overall, we observed 17 elasmobranch species, 15 of which were recorded on shallow dives (50–100 m) and 11 on deep dives (300–400 m). We found a decreasing trend in the probability of occurrence of Carcharhinus falciformis over time (2010–2019), while other species (e.g. Taeniurops meyeni, Sphyrna lewini, Carcharhinus galapagensis, Triaenodon obesus, and Galeocerdo cuvier) showed an increasing trend. Our study suggests that some species like S. lewini may be shifting their distributions towards deeper waters in response to ocean warming but may also be sensitive to low oxygen levels at greater depths. These findings highlight the need for regional 3D environmental information and long-term deepwater surveys to understand the extent of shark and ray population declines in the ETP and other regions, as most fishery-independent surveys from data-poor countries have been limited to relatively shallow waters.
... Other methods have also been used to assess post-release mortality in other fisheries, such as qualitative health assessments (Benoît et al. 2010b(Benoît et al. , 2013 ) and blood-physiology studies (Skomal 2007, Gallagher et al. 2014a, Campbell et al. 2018, Whitney et al. 2021 ), but they may not be necessarily relevant to quantify post-release survival estimates (Ellis et al. 2017 ) since they only rely on immediate assessment although death can occur few hours, weeks, or months after releases. However, including health assessment or blood physiology as covariates in CMR models could help identify physical or physiological proxies of post-release survival. ...
Whiteleg skate (Amblyraja taaf) is a bycatch species commonly discarded in demersal longline fisheries targeting Patagonian toothfish around the Crozet archipelago (Southern Ocean). While there are global conservation issues on elasmobranchs, the post-release survival of this deep-sea species remains unknown. This study is the first tagging programme conducted on Whiteleg skates to in vestigate their fate after being released at sea. Almost 3000 skates were captured, double-tagged with conventional tags and released between 2020 and 2022 to assess survival using capture-mark-recapture (CMR) models. Our primary result was an estimated annual apparent survival rate higher than 92% for skates released in good condition (with 185 skates recaptured after up to 944 days at liberty). Low detection rate highlighted methodological challenges for CMR models. However, skate size and depth of capture had an effect on apparent survival probability with smaller individuals having lower values (< 65 cm; 0.84 ± 0.04) as well as skates caught at shallower depths (< 1200 m; 0.83 ± 0.04). Overall, this study suggests that the mandated release of skates in good condition is effective to limit fishing impact on skates in this fishery. To further limit this impact, we recommended changes in fishing practices (hauling speed and soak time).
... These species are frequently targeted in specific fisheries and fall victim to bycatch (Zeeberg et al. 2006;Okes and Sant, 2019), comprising a significant component of the fin trade (Dent and Clarke, 2015;Fields et al., 2018;Cardenosa et al., 2022). Furthermore, the mortality rates associated with high capture stress further threatens the survival of these species (Gallagher et al. 2014;Ellis et al., 2017). Adding to this, these species are often broadly categorized as multiple hammerhead shark species, "Hammerhead sharks nei", or "Unspecified Hammerhead" in catch data (Dicken et al. 2018;Okes and Sant, 2019), which poses further challenges for conducting species-specific stock assessments (Clarke et al., 2006) and accurately monitoring hammerhead shark population trends. ...
Globally, hammerhead sharks have experienced severe declines owing to continued overexploitation and anthropogenic change. The smooth hammerhead shark Sphyrna zygaena remains comparatively understudied compared to other members of the family Sphyrnidae, and despite its Vulnerable status, a comprehensive understanding of its genetic landscape remains lacking. The present study aimed to conduct a fine-scale genomic assessment of Sphyrna zygaena within the highly dynamic marine environment of South Africa’s coastline, using thousands of single nucleotide polymorphisms (SNPs) derived from restriction site-associated DNA sequencing (3RAD). A combination of differentiation-based outlier detection methods (OUTFlank and pcadapt) and Genotype-Environment Association (GEA) (Redundancy Analysis) analysis in Sphyrna zygaena were employed. Subsequent assessments of putatively adaptive loci revealed a distinctive south to east genetic cline. Amongst these, notable correlations between adaptive variation and sea-surface dissolved oxygen and salinity, in addition to spatial factors were evident. Conversely, analysis of 110, 965 neutral SNP markers revealed a lack of regional population differentiation, a finding that remained consistent across various analytical approaches, including an assessment of isolation-by-distance (IBD) and isolation-by-environment (IBE), genetic clustering analyses (LEA, fastSTRUCTURE, and find.clusters), and a discriminant analysis of principal components (DAPC). These results provide evidence for the presence of differential selection pressures within a limited spatial range, despite high gene flow implied by the selectively neutral dataset. This study offers notable insights regarding the potential impacts of genomic variation in response to fluctuating environmental conditions in the circumglobally distributed Sphyrna zygaena.
... In fisheries using good handling practices and where live sharks must be released, wire leaders may lead to less post-release mortality due to the reduction of gear left in sharks (Gilman et al. 2016b). Alternately, if time on the line is the more significant predictor of mortality (Gallagher et al. 2014), monofilament leaders may be optimal. Comparing the probability of shark survival after escaping from monofilament leaders with an ingested hook and trailing line versus when captured on wire leaders has been flagged as a research priority for pelagic sharks (Gilman et al. 2016a). ...
The North Atlantic Designatable Unit (DU) of Shortfin Mako Shark was assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as Endangered in April 2019, and is currently under consideration for listing under Schedule 1 of the Species at Risk Act (SARA). The Recovery Potential Assessment (RPA) presented here provides information to support the listing recommendation and any recovery actions, should the species be listed.
Shortfin Mako occurs throughout the Northern Hemisphere of the Atlantic Ocean. The biological characteristics of Shortfin Mako (i.e., relatively long lifespan, late maturity, and low reproductive output) make the population very susceptible to fishing pressure, which is the main threat identified in the North Atlantic. Multiple international and Canadian fisheries intercept Shortfin Mako as bycatch, and the most recent assessment of the DU predicts that it is overfished relative to biomass at Maximum Sustainable Yield (MSY). Reducing total removals in the North Atlantic to 500 mt is projected to have a > 50% probability of population recovery by 2070. For comparison, international and Canadian removals in 2019 totaled 1,863 mt and 63 mt, respectively. Considering just Canadian fleets, interception probabilities are highest from pelagic longline, with an average of 48% of observed sets encountering Shortfin Mako, followed by bottom longline (0.4% of sets) and otter trawl (0.2% of sets).
The most effective Canadian mitigation measure for Shortfin Mako will be the new landings prohibition, implemented in 2020 for pelagic longline and scheduled for implementation in 2021 for fixed-gear groundfish fisheries. The effectiveness of other mitigation measures are relatively unclear and, in many cases, would require dedicated experimentation to test. The current requirement to use circle hooks may need to be revised due to new evidence that increased catchability outweighs any reduction in post-release mortality for Shortfin Mako, thus leading to greater total mortality as compared to using J-hooks. Given the current level of international fisheries removals and the extent of mitigation already in place in Canada, there is very little scope for mitigation actions by Canada to measurably affect recovery potential.
... Like S. lewini it has been caught both as target and bycatch in coastal and pelagic fisheries, but is more often retained for its fins, which are larger than those of S. lewini (Rigby et al., 2019b). This species appears more sensitive to the stress of capture with a high post-release mortality rate (Gallagher et al., 2014a). ...
The scalloped hammerhead shark (Sphyrna lewini), a critically endangered species with a decreasing global population, is characterised by its occurrence in large schools. Such schools are still observed today in the Pacific Ocean, but this is generally not the case in the Atlantic Ocean, and in the Cayman Islands not since the 1970s. Here we report a recent record of a school of S. lewini in deep water off Grand Cayman, and describe a recent, concomitant increase in numbers of the species, and its critically endangered congener, the great hammerhead (Sphyrna mokarran), around the Cayman Islands. Relative population trends and seasonal patterns were assessed using data from shallow and deep-water BRUVS, scientific longlining, citizen science projects including the Sharklogger Network and REEF, and social media reports. It appears that S. lewini may be slowly re-occupying the area, selecting and using deeper waters to school, while S. mokarran has also become less scarce than hitherto.
... While electronic tagging of pelagic sharks can help obtain information on vertical habitat use (Andrzejaczek et al. 2022), this process is time-intensive and can impose physiological challenges to captured individuals. These challenges may result in behavioral modifications and survival difficulties after release (Gallagher et al. 2014). Moreover, achieving robust sample sizes in areas of the deep ocean presents numerous logistical and operational issues, reinforcing the value of additional methods for observing the behavioural habits of pelagic sharks in the deep ocean. ...
Studying the behavior of pelagic sharks can be challenging due to the logistical difficulties of locating migratory individuals in the open ocean. This is further compounded by their rarity in certain ocean regions due to overfishing. The accessibility of deep-water basins in The Bahamas provides a unique model system for describing how pelagic sharks connect surface and deep ocean habitats through vertical behavior. Using custom deep-sea landers in The Bahamas, we obtained novel depth data for two species of pelagic sharks: the bignose shark at 767 m and the silky shark at 470 m. These new observations support and corroborate previous vertical niche records for these two species, suggesting that deep diving behavior is likely more common than previously thought and likely important for ecosystem connectivity.
... However, since S. lewini and its congeners, the great hammerhead (Sphyrna mokarran) and the smooth hammerhead (Sphyrna zygaena), are prohibited from harvest in Florida waters, the risk from recreational fishing is likely to be limited. Still, because they have been shown to exhibit high rates of at-vessel and post-release mortality due to a pronounced capture stress response (Morgan and Burgess, 2007;Morgan and Carlson, 2010;Gulak et al., 2015;Gallagher et al., 2014), the possibility for unintended mortality related to catch-and-release fishing remains present. Therefore, information on the temporal and spatial patterns of YOY S. lewini habitat use in the Tolomato River may be useful for reducing negative fishery interactions with these species, e.g., by avoidance of high use areas during the period of occurrence. ...
... Once hooked, sharks were allowed to swim with the line and poly ball, closely followed by the boat, for approximately 10 min before being brought to the side of the boat. This tired the shark to the point that it could be handled safely while keeping fight times short enough to minimize the physiological stress response (Gallagher et al. 2014;Gulak et al. 2015). ...
Objective
Shark depredation, the full or partial consumption of a hooked fish by a shark before it is landed, is an increasing source of human–wildlife conflict in recreational fisheries. Reports of shark depredation in the catch‐and‐release Tarpon (also known as Atlantic Tarpon) Megalops atlanticus fishery in the Florida Keys are increasing, specifically in Bahia Honda, a recreational fishing hot spot and a putative Tarpon prespawning aggregation site.
Methods
Using visual surveys of fishing in Bahia Honda, we quantified depredation rates and drivers of depredation. With acoustic telemetry, we simultaneously tracked 51 Tarpon and 14 Great Hammerheads (also known as Great Hammerhead Sharks) Sphyrna mokarran , the most common shark to depredate Tarpon, to quantify residency and spatial overlap in Bahia Honda.
Result
During the visual survey, 394 Tarpon were hooked. The combined observed shark depredation and immediate postrelease predation rate was 15.3% for Tarpon that were fought longer than 5 min. Survival analysis and decision trees showed that depredation risk was highest in the first 5–12 min of the fight and on the outgoing current. During the spawning season, Great Hammerheads shifted their space use in Bahia Honda to overlap with Tarpon core use areas. Great Hammerheads restricted their space use on the outgoing current when compared to the incoming current, which could drive increased shark–angler interactions.
Conclusion
Bahia Honda has clear ecological importance for both Tarpon and Great Hammerheads as a prespawning aggregation and feeding ground. The observed depredation mortality and postrelease predation mortality raise conservation concerns for the fishery. Efforts to educate anglers to improve best practices, including reducing fight times and ending a fight prematurely when sharks are present, will be essential to increase Tarpon survival and reduce shark–angler conflict.
... The shark that was the subject of the present study returned to this yo-yo pattern of movement within a similar time frame, implying that stomach eversion and retraction did not create any further adverse effects beyond those of capture and restraint. However, resilience to capture is a recognized feature of tiger sharks (Mandelman and Skomal, 2009;Gallagher et al., 2014;Whitney et al., 2021) and this outcome may not necessarily be replicated by other species that are more prone to mortality during capture (e.g., hammerhead sharks, Sphyrna sp.; Gulak et al., 2015). Our study shows that video and accelerometer tags may provide a useful means to monitor and assess behaviours such as stomach retraction that are otherwise very difficult to document. ...
... The removal of lactate is an important component of post-exercise recovery. Fighting the hook during capture depletes glycogen stores and generates lactate [8,9], possibly leading to acidosis [10,11]. In turn, postrelease recovery replenishes glycogen stores, removes lactate and restores homeostasis [10,12,13]. ...
Landscapes of fear describe a spatial representation of an animal's perceived risk of predation and the associated foraging costs, while energy landscapes describe the spatial representation of their energetic cost of moving and foraging. Fear landscapes are often dynamic and change based on predator presence and behaviour, and variation in abiotic conditions that modify risk. Energy landscapes are also dynamic and can change across diel, seasonal, and climatic timescales based on variability in temperature, snowfall, wind/current speeds, etc.
Recently, it was suggested that fear and energy landscapes should be integrated. In this paradigm, the interaction between landscapes relates to prey being forced to use areas of the energy landscape they would avoid if risk were not a factor. However, dynamic energy landscapes experienced by predators must also be considered since they can affect their ability to forage, irrespective of variation in prey behaviour. We propose an additional component to the fear and dynamic energy landscape paradigm that integrates landscapes of both prey and predators, where predator foraging behaviour is modulated by changes in their energyscape.
Specifically, we integrate the predator's energy landscape into foraging theory that predicts prey patch‐leaving decisions under the threat of predation. We predict that as a predator's energetic cost of foraging increases in a habitat, then the prey's foraging cost of predation and patch quitting harvest rate, will decrease. Prey may also decrease their vigilance in response to increased energetic foraging costs for predators, which will lower giving‐up densities of prey.
We then provide examples in terrestrial, aerial, and marine ecosystems where we might expect to see these effects. These include birds and sharks which use updrafts that vary based on wind and current speeds, tidal state, or temperature, and terrestrial predators (e.g. wolves) whose landscapes vary seasonally with snow depth or ice cover which may influence their foraging success and even diet selection.
A predator perspective is critical to considering the combination of these landscapes and their ecological consequences. Dynamic predator energy landscapes could add an additional spatiotemporal component to risk effects, which may cascade through food webs.
Read the free Plain Language Summary for this article on the Journal blog.
... Hammerhead sharks (Sphyrna sp.) are often targeted in fisheries due to their large fibrous fins, which is a desirable characteristic for the Asian dish 'shark fin soup' [12]. They are particularly vulnerable to fishing due to their aggregating behaviour [23] and high mortality rates, even when released after capture [24]. ...
... Great hammerhead sharks are particularly vulnerable to anthropogenic pressures such as commercial (targeted and bycatch) and recreational fisheries due to their k-selected life-history characteristics, i.e., late maturity (8 -20 years of age) (Corteś, 2000;Harry et al., 2011), low fecundity (litter size ranging 6 -42 pups) (Compagno, 1984;Stevens and Lyle, 1989), slow growth (k = 0·079 -0·11) (Piercy et al., 2010;Harry et al., 2011), and long gestation periods (10 -11 months) (Stevens and Lyle, 1989;Harry et al., 2011) which occurs on a biennial reproductive cycle (Stevens and Lyle, 1989). Great hammerhead sharks also suffer from high atvessel and post-release mortality due to an elevated stress response to capture (Morgan and Burgess, 2007;Gallagher et al., 2014). High likelihood of post-release mortality and slow life-history traits combined with increasing anthropogenic pressures has led to population decline across the species range and to great hammerhead sharks being globally listed as Critically Endangered on the IUCN (International Union for Conservation of Nature) Red List of Threatened Species (Rigby et al., Most studies on great hammerhead sharks have been conducted in the northwest Atlantic Ocean (Piercy et al., 2010;O'Connell and Leurs, 2015;Guttridge et al., 2017;Doan and Kajiura, 2020;Heim et al., 2021;Macdonald et al., 2021), southwest Pacific Ocean (Stevens and Lyle, 1989;Harry et al., 2011;Raoult et al., 2019), and to a lesser extent in the Western Indian Ocean (Cliff, 1995) and in the Arabian Gulf (Hsu et al., 2020). ...
The occurrence and seasonality of the Critically Endangered great hammerhead shark, Sphyrna mokarran, is data deficient in the Central Pacific region. Using photo-identification and laser-photogrammetry, we describe the seasonal population of great hammerhead sharks in the Tiputa pass (Rangiroa atoll) and Tuheiava pass (Tikehau atoll) in the Tuamotu archipelago of French Polynesia. During the austral summer of 2020 and 2021, we recorded a female-biased aggregation of at least 55 individuals (54 females; 1 unknown sex), representing an unprecedented number of S. mokarran in one study. All measured sharks were likely mature with pre-caudal lengths ranging from 147 cm to 297 cm (n = 35). Videos from citizen scientists recorded over a 15-year period enable us to identify 30 additional individuals between 2006 and 2019, with strong evidence of sexual segregation during the year. Our findings revealed seasonal residency (n = 32) of up to 6 days/month and for up to 5 months at the study site during the austral summer. We also demonstrated site fidelity with 32 individuals returning to the same atoll for up to 12 years between the first and last sighting, and with limited evidence of connectivity between the two sites. Our analysis also provides preliminary insight into the environmental factors driving S. mokarran aggregation in the Tiputa pass, suggesting a marked influence of the lunar cycle and of ocellated eagle rays (Aetobatus ocellatus) abundance. This study, conducted in situ with non-invasive methods offers a unique opportunity to study a great hammerhead shark population in a near-pristine ecosystem and provides important life-history elements for the Central Pacific region.
... However, to date, few studies have documented this Kieffer et al., 1995;Dinken et al., 2022). Furthermore, Gallagher et al. (2014) found that fight time could not predict blood pCO 2 levels in several shark species. Our study offers additional evidence that some fish species may not experience severe hypercapnia during C&R, as we found no changes in cahz, nhe1 and nka-a1 mRNA levels at any sampling point. ...
Catch-and-release (C&R) angling is a conservation-oriented practice intended to reduce the impact recreational angling has on fish populations. Even though most recreationally angled fish are released, little is known about how C&R angling impacts fish at the cellular or tissue level. As the first to explore the impacts of C&R angling on mRNA abundances, our study aimed to identify how the stress of angling influenced metabolism, acid–base regulation and cellular stress in the gills of lake trout (Salvelinus namaycush). Because gills are responsible for metabolic gas exchange, are crucial sites of acid–base homeostasis and respond to stressors quickly, we hypothesized that the relative mRNA abundance of genes related to these three physiological processes would be altered after angling. We took gill samples of live lake trout at 0, 2 or 48 h after fish were angled by rod and reel, and then used quantitative PCR (qPCR) to measure the relative abundance of nine candidate mRNA transcripts. Heat shock protein 70 (hsp70) mRNA levels significantly increased over 5-fold 2 h after angling, indicating a potential activation of a cytoprotective response. However, contrary to our hypothesis, we observed no change in the relative mRNA abundance of genes related to metabolism or acid–base regulation in response to C&R angling within a 48-h period. As C&R angling can negatively impact fish populations, further use of transcript-level studies will allow us to understand the impact C&R has on specific tissues and improve our knowledge of how C&R influences overall fish health.
... Consequently, captured hammerhead sharks may have to exert additional energy to ensure sufficient oxygen flow over their gills, resulting in elevated stress levels and eventual mortality (Gulak et al. 2015). Secondly, a recent study of 5 coastal shark species determined the great hammerhead to be most susceptible stress caused by fishing due to high lactate levels (a proxy for stress response, Gallagher et al. 2014c). It is unequivocal that avoidance of fishery interactions is the best option for reducing mortality to hammerhead sharks. ...
Scalloped hammerhead sharks Sphyrna lewini are a circumglobal species found in tropical and subtropical waters. Globally, populations of S. lewini have undergone dramatic declines in recent decades, and 4 of 6 distinct population segments are at risk of extinction and listed under the United States Endangered Species Act. Despite this, limited data exist on movement behavior or habitat use requirements of S. lewini , especially in the Central Pacific region. In this long-term (2009-2020) telemetry study, 27 S. lewini (24 males [22 adults, 2 juveniles], and 3 juvenile females) ranging in size from 106 to 310 cm (total length) were tagged with a combination of acoustic and/or satellite tags in a known nursery area, Kāne‘ohe Bay, Hawai‘i. Acoustic data revealed repeated movements of adult male S. lewini to Kāne‘ohe Bay between May and September across multiple years. Horizontal movements away from the Bay indicate these individuals are highly associated with the Hawaiian Archipelago (i.e. Northwestern and main Hawaiian Islands), while vertical movements were dynamic, with repeated, nocturnal deep dives to depths beyond 800 m and temperatures as low as 5.0°C. We conclude that adult male and juvenile S. lewini tagged in Kāne‘ohe Bay exhibit fairly restricted movements throughout the Hawaiian Archipelago, and mature males specifically exhibit strong seasonal site fidelity to Kāne‘ohe Bay. These data add crucial baseline information on habitat preferences of S. lewini around the Hawaiian Islands, and can be used to help structure conservation strategies for a portion of the Central Pacific population.
... En los palangres demersales de Australia occidental se estima que la mortalidad es del 30,8 % (Braccini y Waltrick, 2019). Gallagher et al. (2014) sugieren una tasa de mortalidad posterior a la liberación del 50 %, probablemente debido a una respuesta de estrés conductual y fisiológica pronunciada por los combates en una línea de pesca, incluso durante períodos de tiempo relativamente cortos, siendo de las especies con una de las mayores vulnerabilidades a la mortalidad en el barco y después de la liberación. Morgan y Burgess 2007 también observaron en buques palangreros comerciales de fondo en el Atlántico noroeste y el golfo de México que el 93,8 % de los individuos de cornuda gigante estaban muertos cuando se subieron a bordo. ...
Una revisión de la ecología y biología pesquera de la cornuda gigante (Sphyrna mokarran), con especial énfasis en el Océano Atlántico y mares adyacentes.
... For demersal longlines in western Australia, mortality is estimated at 30.8% (Braccini and Waltrick, 2019). Gallagher et al. (2014) suggested a post-release mortality of 50%, probably due to a pronounced behavioural and physiological stress response caused by struggles in a fishing line, even during relatively short periods of time, and the great hammerhead is one of most vulnerable species to mortality on the boat and following release. Morgan and Burgess (2007) also observed that 93.8% of great hammerhead individuals were dead when taken on board in commercial bottom longline vessels in the Northwest Atlantic and Gulf of Mexico. ...
A review of the ecology and fishery biology of the great hammerhead shark (Sphyrna mokarran), with a special focus on the Atlantic Ocean and adjacent seas.
... This contact induces stress, which is likely to alter the natural behaviour of the animals examined, as well as potentially impairing their welfare (Murray et al., 2020). In addition, the capture, restraint and, in some cases, removal of the animal from water, required to facilitate traditional ultrasonographic examination, are often difficult and unacceptable when studying endangered species (Gallagher et al., 2014;Mohan et al., 2020). As a result, ultrasonography has been used only in two published studies on captive M. alfredi: firstly to demonstrate how embryos obtain oxygen in utero (Tomita et al., 2012) and secondly to monitor embryonic development (Murakumo et al., 2020). ...
The ability to visualise the internal anatomical structures of fish provides important information on their reproductive status and body condition and has made important contributions to many areas of fish biology. Obtaining information on the internal anatomy of fish has traditionally required euthanasia and dissection. Although ultrasonography is now increasingly used to study internal fish anatomy without the need for euthanasia, traditional techniques still require restraint and contact with the animal, both of which are known to cause stress. This has prompted the development of waterproof, contactless and portable equipment to allow ultrasonographic examinations to be carried out in free‐swimming individuals, which also facilitates the application of this tool in wild populations of endangered species. This study reports the validation of this equipment using anatomical examinations of nine manta and devil ray (Mobulidae) specimens landed at fish markets in Sri Lanka. The species studied were Mobula kuhlii (n = 3), Mobula thurstoni (n = 1), Mobula mobular (n = 1), Mobula tarapacana (n = 1) and Mobula birostris (n = 3). The use of this equipment was further validated with ultrasonographic examinations in 55 free‐swimming reef manta rays Mobula alfredi, which enabled maturity status to be quantified in 32 females. Structures successfully identified in free‐swimming individuals were the liver, spleen, gallbladder, gastrointestinal tract, skeletal structures, developing follicles and uterus. The study demonstrated that ultrasonography provided a reliable method of determining both sexual maturity and gestational status in free‐swimming M. alfredi. The methodology induced no detectable signs of disturbance to the animals involved and therefore offers a viable and practical alternative to invasive techniques currently used to study anatomical changes in both captive and wild marine organisms.
... The smooth hammerhead sharks are prone to the effects of overfishing (Rigby et al., 2019) and have a high postrelease mortality rate due to stress (e.g. Gallagher et al., 2014). Smooth hammerhead sharks are not a target species under the New Zealand Fisheries Act 1996, yet it is often reported as bycatch (Francis, 2016). ...
Aim
Large marine predators, such as cetaceans and sharks, play a crucial role in maintaining biodiversity patterns and ecosystem function, yet few estimates of their spatial distribution exist. We aimed to determine the species richness of large marine predators and investigate their fine‐scale spatiotemporal distribution patterns to inform conservation management.
Location
The Hauraki Gulf/Tīkapa Moana/Te Moananui‐ā‐Toi, Aotearoa/New Zealand.
Methods
We conducted a replicate systematic aerial survey over 12 months. Flexible machine learning models were used to explore relationships between large marine predator occurrence (Bryde's whales, common and bottlenose dolphins, bronze whaler, pelagic and immature hammerhead sharks) and environmental and biotic variables, and predict their monthly distribution and associated spatially explicit uncertainty.
Results
We revealed that temporally dynamic variables, such as prey distribution and sea surface temperature, were important for predicting the occurrence of the study species and species groups. While there was variation in temporal and spatial distribution, predicted richness peaked in summer and was the highest in coastal habitats during that time, providing insight into changes in distributions over time and between species.
Main Conclusions
Temporal changes in distribution are not routinely accounted for in species distribution studies. Our approach highlights the value of multispecies surveys and the importance of considering temporally variable abiotic and biotic drivers for understanding biodiversity patterns when informing ecosystem‐scale conservation planning and dynamic ocean management.
... Previous studies using capture and release methods with other obligate ram ventilators have described identical recovery patterns [6,29]. Sharks #01 and #02 may have shifted from aerobic to anaerobic metabolism during the strenuous process of fishing, restraining and tagging, thus consuming their glycogen stocks and accumulating lactate [30,31]. One way to reduce lactate accumulation is via oxidation, which may be achieved faster by increasing the active metabolic rate and oxygen uptake (e.g. by elevating swimming speeds immediately after release) [29]. ...
As regional endotherms, lamnid sharks can sustain high cruising speeds and perform frequent speed bursts. However, since endothermy comes with high energetic costs, lamnids may adopt different swimming strategies to manage their energy budget. Understanding such strategies is essential to provide behavioural and physiological context to their broader movement ecology. The endangered shortfin mako (Isurus oxyrinchus) possibly has the highest energy requirements among lamnids, but our understanding of its swimming behaviour is still limited. We equipped three shortfin mako sharks with high-resolution multi-sensor tags to measure their swimming kinematics in the wild. While swimming horizontally, individuals favoured tail-beat frequencies around 0.6 Hz at speeds comparable to those of ectothermic sharks (ca 0.5 m s⁻¹). All individuals displayed yo-yo-like diving patterns where, for a given tail-beat frequency, speeds were higher during descents, as expected for a negatively buoyant fish. Contrary to what was expected, gliding was almost absent (less than 1.31%). Speed bursts reaching up to 3.6 m s⁻¹ were observed during the day but ceased shortly after dusk, implying a diel change in swimming behaviour. As large-scale research efforts are hindered by this species' increasing rarity, opportunistic high-resolution datasets, like the present, are fundamental to improve our understanding of shortfin mako's behaviour and ecology.
... In the southwestern Pacific region, a previous study using commercial fishing records and research trawl surveys estimated that the species inhabits shallow coastal areas for about 2 years based on individuals fishing location and age determination (Francis, 2016). schooling, alternation between coastal and pelagic habitats) specificities (Braccini et al., 2022;Gallagher, Serafy, et al., 2014). The present study suggests that smooth hammerhead sharks share one of these behavioural traitslong periods of coastal residency, which increase the vulnerability to artisanal fisheries accounting for the majority of the shark captures in the Pacific coast of Mexico (Cartamil et al., 2011;Ramírez-Amaro et al., 2013). ...
The management of migratory taxa relies on the knowledge of their movements. Among them, ontogenetic habitat shift, from nurseries to adult habitats, is a behavioural trait shared across marine taxa allowing resource partitioning between life stages and reducing predation risk. As this movement is consistent over time, characterizing its timing is critical to implement efficient management plans, notably in coastal areas to mitigate the impact of fisheries on juvenile stocks.
In the Mexican Pacific, habitat use of the smooth hammerhead shark (Sphyrna zygaena) is poorly described, while the species is heavily harvested. Given the large uncertainties associated with the timing of out‐migration from coastal nursery grounds to offshore waters prior to reproductive maturity, a more precise assessment of smooth hammerhead shark movements is needed.
Photochemical degradation of mercury imparts mass‐independent isotope fractionation (Δ¹⁹⁹Hg) which can be used to discriminate between neonate coastal shallow habitats and the offshore deep foraging patterns of late juveniles. Here, we present the application of muscle Δ¹⁹⁹Hg as molecular clocks to predict the timing of ontogenetic habitat shifts by smooth hammerhead sharks, based on their isotopic compositions at the initial and arrival habitats and on muscle isotopic turnover rate.
We observed decreases in Δ¹⁹⁹Hg values with shark body length, reflecting increasing reliance on offshore mesopelagic prey with age. Coastal residency estimates indicated that smooth hammerhead sharks utilize coastal resources for 2 years prior to offshore migration, suggesting a prolonged residency in these ecosystems.
Policy implications. This study demonstrates how mercury stable isotopes and isotopic clocks can be implemented as a complementary tool for stock management by predicting the timing of animal migration—a key aspect in the conservation of marine taxa. In the Mexican Pacific, fishing pressure on shark species occurs in coastal habitats depleting juvenile stocks. Consequently, management decision support tools are imperative for effectively maintaining early life stage population levels over time. The finding that smooth hammerhead sharks extensively rely on highly fished habitats for 2 years after parturition supports the relevance of establishing a size limit in coastal fisheries and demonstrates how the current temporal shark fishing closure could lack efficiency for the species.
... Independientemente de las medidas de gestión implementadas, se debe disponer de datos precisos sobre las capturas incidentales de tiburones ETP (además de marrajo azul) si se quiere reducir efectivamente las interacciones con los artes de pesca en el futuro, especialmente porque las prohibiciones de retención a bordo no logran reducir eficientemente la mortalidad (Gallagher et al., 2014a(Gallagher et al., , 2014b. ...
In the present work, key aspects of the biology and ecology of the shortfin mako were studied. Feeding habits, analysed in two ocean basins, indicated that pelagic fish and cephalopods were the main prey items. In the South Pacific Ocean, a marked sexual segregation was found, with females being more common in the SE region; this was also the area with a higher abundance of juveniles and of late-stage pregnant females. In the North Atlantic Ocean, large-scale horizontal movements (including trans-Atlantic migrations) were identified and diel vertical behaviour patterns described. Importantly, individuals that performed wider movements away from the tagging location were less at risk from surface longline fishing. Using tagging and recapture data that spanned a ten-year period, survival, dispersal, and fishing mortality rates for both mako and blue sharks were estimated. The presence of plastics and hooks was also observed for both species, in two studied ocean basins. Finally, bycatch rates for other internationally protected shark species that are commonly caught using surface longlines was estimated based on direct observations, which were several times higher than the official reported data. The results presented here are especially relevant for improving the management measures focused on pelagic sharks.
... Similarly, fish caught and tagged on commercial longline vessels have reduced survival the longer the time-period is between hooking and retrieval [61,71,73]. Disruption of physiological homeostasis associated with capture is also common in fishes (e.g., [35,60,94]). For example, elevated plasma cortisol, lactate, and plasma ion levels have been recorded as are common when times from hooking to sampling (i.e., "fight times") exceeded 10 min (e.g., [53,58,90]). ...
Archival (data-storage) and telemetry (acoustic and radio) tags are commonly used to provide data on the behavior and physiology of organisms, as well as data on their surrounding environment. For fishes, it is often advantageous to implant tags in the peritoneal cavity (i.e., intracoelomic implantation). The literature on best practices is limited for marine species, and near absent for tunas despite their regular application. We identify recommended practices using laparotomy in tropical tuna species following observations from thousands of tags implantations undertaken during implementation of several tagging programs across the Pacific. These recommended practices include descriptions of preferred tagging stations and equipment, fish selection, surgical procedures, and return of the fish to the wild. While these recommended practices were developed specifically for tropical tuna species, they are also likely applicable for other pelagic fishes. We present these guidelines to guide and promote the development of best practices for such procedures on pelagic species.
Catch-and-release angling is a popular recreational pastime and an essential component of many fish research programmes. Marked physiological disturbances have been documented in elasmobranchs in response to angling and handling, but skates and rays remain understudied. Here, we describe for the first time the physiological responses of the critically endangered flapper skate (Dipturus intermedius) to angling, handling and tagging in Scotland. Sixty-one skate were captured by angling as part of a tagging research programme. We assessed individual health, measured blood parameters at two time points (post-capture and prior to release) and recorded heart and respiratory rates during handling and the surgical insertion of acoustic tags. Injuries or infections were identified in 10% of individuals and attributed to prior angling in two cases. Skate generally experienced a mild metabolic acidosis characterized by decreases in blood pH and bicarbonate and increases in lactate and glucose. Respiratory acidosis characterized by limited increases in PCO2 was also observed. The degree of acidosis was greater with warmer sea temperatures and longer fight times, and worsened during the time that skate were handled on deck. Heart rates during handling were negatively associated with body size, positively associated with temperature and also linked to time on the line. Taken together, our results suggest that elevated fight times and temperatures increase the physiological stress experienced by rod and reel-caught flapper skate. Efforts to reduce fight times and minimize heat exposure (including shading, irrigation and reduced handling time) should be beneficial for skate.
Overlap between marine megafauna and maritime activities is a topic of global concern. Basking sharks (Cetorhinus maximus; CM) are listed as Globally Endangered under the IUCN, though reported sightings appear to be increasing in Ireland. While such trends in the region are welcome, increasing spatiotemporal overlap between CM and numerous water users poses an increased risk of boat strikes to the animals. To demonstrate the risk and impact of boat strikes on marine megafauna, we present camera-enabled animal-borne inertial measurement unit (IMU) data from a non-lethal boat strike on a CM within a proposed National Marine Park in Ireland. We tagged a ~7-m female CM in County Kerry, Ireland, which was struck by a boat ~6 h after tag deployment. Comparison of pre-strike data with 4 h of video and ~7.5 h of IMU data following the boat strike provides critical insight into the animal’s response. While the CM reacted momentarily with an increase in activity and swam to the seafloor, it quickly reduced its overall activity (i.e., overall dynamic body acceleration, tailbeat cycles, tailbeat amplitude, and vertical velocity) for the remainder of the deployment. Notably, the animal also ceased feeding for the duration of the video and headed towards deep offshore waters, which is in stark contrast to the pre-strike period where the animal was consistently observed feeding along the surface in shallow coastal water. This work provides insight into a CM’s response to acute injury and highlights the need for appropriate protections to mitigate risks for marine megafauna.
Per- and polyfluoroalkyl substances (PFAS) enter the marine food web, accumulate in organisms, and potentially have adverse effects on predators and consumers of seafood. However, evaluations of PFAS in meso-to-apex predators, like sharks, are scarce. This study investigated PFAS occurrence in five shark species from two marine ecosystems with contrasting relative human population densities, the New York Bight (NYB) and the coastal waters of The Bahamas archipelago. The total PFAS (∑PFAS) concentrations in muscle tissue ranged from 1.10 to 58.5 ng g-1 wet weight, and perfluorocarboxylic acids (PFCA) were dominant. Fewer PFAS were detected in Caribbean reef sharks (Carcharhinus perezi) from The Bahamas, and concentrations of those detected were, on average, ~79% lower than in the NYB sharks. In the NYB, ∑PFAS concentrations followed: common thresher (Alopias vulpinus) > shortfin mako (Isurus oxyrinchus) > sandbar (Carcharhinus plumbeus) > smooth dogfish (Mustelus canis). PFAS precursors/intermediates, such as 2H,2H,3H,3H-perfluorodecanoic acid and perfluorooctanesulfonamide, were only detected in the NYB sharks, suggesting higher ambient concentrations and diversity of PFAS sources in this region. Ultra-long-chain PFAS (C≥10) were positively correlated with nitrogen isotope (δ15N) and total mercury in some species. Our results provide some of the first baseline information on PFAS concentrations in shark species from the northwest Atlantic Ocean and correlations between PFAS, stable isotope, and mercury further contextualize the drivers of PFAS occurrence.
Effective management and conservation of threatened species biodiversity requires knowledge of reproductive biology, such as cyclicity, mode, and age at maturity. We combined reproductive endocrinology and in-situ ultrasonography to examine reproductive characteristics of female Caribbean reef sharks Carcharhinus perezi, a widely distributed, threatened marine predator which remains largely understudied throughout its range. Unique to this study was the opportunity to conduct longitudinal assessments of two individuals, recaptured across multiple seasons during sampling in The Bahamas. Within-individual, paired hormone analyses and in-situ ultrasounds of female sharks that were confirmed as either pregnant, non-pregnant, or reproductively active, suggest a biennial reproductive cycle for Carcharhinus perezi. This unique opportunity to assess the reproductive biology of the same individuals over time underscore the importance of repeated sampling for elucidating population reproductive cyclicity of highly mobile sharks in the wild.
Estimating the survival probability of animals released from fisheries can improve the overall understanding of animal biology with implications for fisheries management, conservation and animal welfare. Vitality indicators are simple visual measures of animal condition that change in response to stressors (like fisheries capture) and can be assessed to predict post-release survival. These indicators typically include immediate reflex responses which are typically combined into a score. Vitality indicators are straight-forward and non-invasive metrics that allow users to quantify how close (or far) an animal is from a normal, ‘healthy’ or baseline state, which in turn can be correlated with outcomes such as survival probability, given appropriate calibration. The literature on using vitality indicators to predict post-release survival of animals has grown rapidly over the past decade. We identified 136 papers that used vitality indicators in a fisheries context. These studies were primarily focused on marine and freshwater fishes, with a few examples using herptiles and crustaceans. The types of vitality indicators are diverse and sometimes taxa-specific (e.g. pinching leg of turtles, spraying water at nictitating membrane of sharks) with the most commonly used indicators being those that assess escape response or righting response given the vulnerability of animals when those reflexes are impaired. By presenting Pacific salmon fisheries as a case study, we propose a framework for using vitality indicators to predict survival across taxa and fisheries.
Age and growth estimates are essential for life history modeling in elasmobranchs and are used to inform accurate conservation and management decisions. The nurse shark (Ginglymostoma cirratum) is abundant in coastal waters of the Atlantic Ocean, yet many aspects of their life history remain relatively understudied, aside from their reproductive behavior. We used mark-recapture data of 91 individual G. cirratum from Bimini, The Bahamas, from 2003 to 2020, to calculate von Bertalanffy (vB) growth parameters, empirical growth rate, and age derived from the resulting length-at-age estimates. The Fabens method for estimating growth from mark-recapture methods was applied through a Bayesian framework using Markov chain Monte Carlo (MCMC) methods. This provided growth parameters with an asymptotic total length (L∞) of 303.28 cm and a growth coefficient (k) of 0.04 yr⁻¹. The average growth rate for G. cirratum was approximately 8.68 ± 6.00 cm yr⁻¹. This study also suggests that the previous maximum age for G. cirratum is likely underestimated, with the oldest individual predicted to be 43 years old. Our study is the first to present vB growth parameters and a growth curve for G. cirratum. It indicates that this species is slow-growing and long-lived, which improves our understanding of their life history.
Until relatively recently commercial fisheries have been considered the main driving factor for elasmobranch population declines. However, this belief has begun to shift with the realization that recreational elasmobranch catches may equal or exceed commercial catches in some regions. Many recreational angling fisheries for elasmobranchs involve high participation in catch-and-release angling practices. However, high release rates may not necessarily equate to high survival rates. Therefore, to assist accurate assessment of the potential impact of recreational angling on elasmobranchs, we attempted to summarize and integrate currently available information on specific risk factors associated with recreational angling, alongside associated mortality rates, as well as information on angler behaviour as it relates to identified risk factors. We categorized the major angling-related effects into two groups: injury-induced effects; and biochemical disruption-induced effects; providing a summary of each group and outlining the main lethal and sub-lethal outcomes stemming from these. These outcomes include immediate and delayed post-release mortality, behavioural recovery periods (which may in-turn confer increased predation risks), chronic health impacts and capture-induced parturition and abortion. Additionally, we detailed a range of angling practices and equipment, including hook-type, hook removal and emersion (i.e. air exposure), as well as inter- and intra-specific factors, including aerobic scope, respiratory mode, body size and species-specific behaviours, which are likely to influence injury and/or mortality rates and should therefore be considered when assessing angling-related impacts. We then utilized these data to provide a range of actionable recommendations for both anglers and policymakers which would serve to reduce the population-level impact of recreational angling on these enigmatic animals.
The assessment of parameters population size and individual home range is important for effective conservation management of sharks. This study uses the novel application of photo identification (photo-ID) to BRUVS footage as a non-invasive alternative to tagging in order to generate individual capture histories. These were used in mark-recapture models to estimate effective population sizes and to determine home ranges. In the Cayman Islands a total of 499 shark sightings of six coastal shark species were recorded on BRUVS from 2015 - 2018, but re-sighting rates were only sufficient for the determination of population parameters for two species - Caribbean reef shark (Carcharhinus perezi) and nurse shark (Ginglymostoma cirratum). The calculated super-population sizes for Caribbean reef shark (180 ± 37 SE) and nurse shark (336 ± 61 SE) were greater than the estimates for each species based on a closed-population model (Caribbean reef shark: 128 ± 40 SE, nurse shark: 249 ± 48 SE), though both measures indicated that there were about twice as many nurse sharks (1.3 - 1.8 sharks/km²) as Caribbean reef sharks (0.7 – 1 shark/km²) within the study area. The demographic compositions included numerous immature individuals, indicating that breeding of both species takes place within the study area of 188 km². Most recognizable individuals of both species showed linear home ranges of <20 km, but a few individuals were observed to have moved longer distances (Caribbean reef shark: 125.37 km, nurse shark: 156.07 km). The data indicate that the home ranges and long-distance movements of individual sharks observed within the islands’ marine protected areas (MPAs) often extend to areas beyond the MPA’s boundary, potentially exposing them to fishing activities. This study provides the first estimates of population size for Caribbean reef and nurse sharks in the Cayman Islands and the first estimate of a Caribbean reef shark population globally.
Background
Bycatch mortality in longline fisheries is a major contributor to global declines in shark populations. The duration of time that an animal is hooked and the impacts of hooking on behavior affect the likelihood of mortality. However, limited information exists on the behavior of sharks to longline capture because of difficulties observing hooking events. Using a fortuitous recovery of an archival satellite tag, we describe the movement of an oceanic whitetip shark (Carcharhinus longimanus) and examine the behavior prior to its mortality in response to hooking on a longline.
Results
A 1.5 m (fork length) C.longimanus was tagged and released in good condition by a fisheries observer following initial capture on a US longline fishing vessel. After release, the shark resumed normal vertical behavior within 5 h. Over 198 days, the shark undertook wide-ranging movements throughout the Pacific between Samoa, Niue, and Tonga. The shark was hooked by a second longline vessel while conducting routine yo-yo diving between 0 and 120 m depth. For the first hour after being hooked the shark exhibited high swimming activity with rapid vertical movements between 20 and 40 m indicative of an initial struggle against the line. After this, the shark struggled at the surface for approximately 5 h, until it succumbed to exhaustion and died on the line.
Conclusion
Fight time has a strong influence on the mortality rates of sharks captured in commercial longline fishing operations. Data obtained from this shark offers further understanding of capture behavior and time to mortality on a longline for C.longimanus which may assist managers as they work on options to reduce mortality rates for this threatened species.
Climate change influences marine environmental conditions and is projected to increase future environmental variability. In the North Atlantic, such changes will affect the behavior and spatiotemporal distributions of large pelagic fish species (i.e., tunas, billfishes, and sharks). Generally, studies on these species have focused on specific climate-induced changes in abiotic factors separately (e.g., water temperature) and on the projection of shifts in species abundance and distribution based on these changes. In this review, we consider the latest research on spatiotemporal effects of climate-induced environmental changes to HMS’ life history, ecology, physiology, distribution, and habitat selection, and describe how the complex interplay between climate-induced changes in biotic and abiotic factors, including fishing, drives changes in species productivity and distribution in the Northwest Atlantic. This information is used to provide a baseline for investigating implications for management of pelagic longline fisheries and to identify knowledge gaps in this region. Warmer, less oxygenated waters may result in higher post-release mortality in bycatch species. Changes in climate variability will likely continue to alter the dynamics of oceanographic processes regulating species behavior and distribution, as well as fishery dynamics, creating challenges for fishery management. Stock assessments need to account for climate-induced changes in species abundance through the integration of species-specific responses to climate variability. Climate-induced changes will likely result in misalignment between current spatial and temporal management measures and the spatiotemporal distribution of these species. Finally, changes in species interactions with fisheries will require focused research to develop best practices for adaptive fisheries management and species recovery.
Understanding how elasmobranchs respond to stressors is imperative so that effective measures to reduce mortality be employed, whether in commercially captured animals or sharks and rays maintained in human care. Currently, reflex action mortality predictors (RAMPs) are the most reliable proxies to indicate an animal's condition state, commonly employed for both teleost and elasmobranchs. As our understanding of mortality predictors is evolving, is it necessary that traditional indicators be constantly reviewed and new proxies proposed, in order to improve the tools available for the best possible evaluation of a stressed individual. In this context, this review aimed to compile data on behavioral and visual proxies, along with the proposition of new proxies to guide professionals and assist them in identifying signs associated with alarming situations that might potentially result in the death of highly stressed individuals or sub-lethal effects at population level (migration, reproduction) that may seriously compromise the success of release measures.
Lactate concentration ([lactate−]), pH, and bicarbonate concentration ([HCO3−]) were measured in the blood of salt-water crocodiles (Crocodylus porosus Schneider) exhausted during field capture. Body temperature after capture averaged 31·1 °C. All animals underwent high levels of anaerobic metabolism and metabolic acidosis. The largest animals attained the highest blood [lactate−] and lowest pH ever observed in any animal as a result of activity. Peak levels of [lactate−] increased with increasing body mass (slope = 9·72 mmol 1−1 logM−1; mass M in kg), indicating a greater anaerobic capacity in larger animals. Several large crocodiles had [lactate−] in excess of 50mmol 1−1. Blood pH decreased with mass (slope = 0·163 pH unitslogM−1) and reached 6·6 in the largest animals. One animal remained acidotic for several hours and had a minimal pH of 6·42. Blood increased significantly and [HCO3−] decreased significantly with increasing body mass. Struggling time before exhaustion was greater in larger animals, ranging from about 5min in small (<1 kg) crocodiles to over 30min in animals over 100 kg. During recovery, mean blood [lactate−] decrement after 2h was 6·0 mmol 1−1 and was not significantly related to mass. Proton elimination from the blood, however, was more rapid in larger animals (slope = 0·0443 μmol 1 −1 log M −1 ). The positive mass-dependence of acid-base disturbance could be related to the greater susceptibility of large crocodiles (>700 kg) to post-capture mortality.
Globally, ecosystems and their constituent flora and fauna face the localized and broad-scale influence of human activities.
Conservation practitioners and environmental managers struggle to identify and mitigate threats, reverse species declines,
restore degraded ecosystems, and manage natural resources sustainably. Scientific research and evidence are increasingly regarded
as the foundation for new regulations, conservation actions, and management interventions. Conservation biologists and managers
have traditionally focused on the characteristics (e.g. abundance, structure, trends) of populations, species, communities,
and ecosystems, and simple indicators of the responses to environmental perturbations and other human activities. However,
an understanding of the specific mechanisms underlying conservation problems is becoming increasingly important for decision-making,
in part because physiological tools and knowledge are especially useful for developing cause-and-effect relationships, and
for identifying the optimal range of habitats and stressor thresholds for different organisms. When physiological knowledge
is incorporated into ecological models, it can improve predictions of organism responses to environmental change and provide
tools to support management decisions. Without such knowledge, we may be left with simple associations. ‘Conservation physiology’
has been defined previously with a focus on vertebrates, but here we redefine the concept universally, for application to
the diversity of taxa from microbes to plants, to animals, and to natural resources. We also consider ‘physiology’ in the
broadest possible terms; i.e. how an organism functions, and any associated mechanisms, from development to bioenergetics,
to environmental interactions, through to fitness. Moreover, we consider conservation physiology to include a wide range of
applications beyond assisting imperiled populations, and include, for example, the eradication of invasive species, refinement
of resource management strategies to minimize impacts, and evaluation of restoration plans. This concept of conservation physiology
emphasizes the basis, importance, and ecological relevance of physiological diversity at a variety of scales. Real advances
in conservation and resource management require integration and inter-disciplinarity. Conservation physiology and its suite
of tools and concepts is a key part of the evidence base needed to address pressing environmental challenges.
From 1994–2005 the Commercial Shark Fishery Observer Program (CSFOP) placed fishery observ-ers aboard US bottom longline vessels engaged in directed fishing for sharks in the region from New Jersey to Louisiana, USA. Observers routinely recorded species specific at-vessel mortality as related to enduring the stress of longline capture. Data for 5 species of sharks (sandbar Carcharhinus plumbeus, blacktip Carcharhinus limbatus, dusky Carcharhinus obscurus, tiger Galeocerdo cuvier, scalloped hammerhead Sphyrna lewini, and great hammer-head Sphyrna mokarran) were analyzed in this study. Multiple stepwise linear regressions indicate that age group, soak time and bottom water temperature can be used as predictors of at-vessel mortality and that size restrictions, size selective gear, restricting the soak time and time/area closures may be beneficial to fisheries targeting large coastal sharks. RESUMEN El Programa de Observación de la Pesquería Comercial de Tiburones sitúo observadores durante el periodo 1994–2005 en naves pesqueras dedicadas específicamente a la pesca con palangre de especies costeras grandes de tiburones en la región comprendida entre los estados de New Jersey y Lousiana en la costa estadoun-idense. Estos observadores tomaron datos sobre la habilidad de diferentes especies para sobrevivir el estrés de la captura con palangre. En este estudio analizamos datos de seis especies (Carcharhinus plumbeus o tiburón trozo, Carcharhinus limbatus o tiburón macuira, Carcharhinus obscurus o tiburón arenero, Galeocerdo cuvieri o tintorera tigre, Sphyrna lewini o cornuda común, y Sphyrna mokarran o cornuda gigante). El múltiplo el retroceso lineal pro-gresivo indican que el uso de restricciones por tamaño, tiempo en el agua, tipo de equipo y el cierre de pesquerías por área o por periodo pueden beneficiar el manejo de las pesquerías de tiburones costeros grandes.
Data collected by fisheries observers aboard U.S. pelagic longline vessels were examined to quantify and describe elasmobranch bycatch off the southeastern U.S. coast (lat. 22°-35°N, long, 71°-82°W). From 1992 to 2000, 961 individual longline hauls were observed, during which 4,612 elasmobranchs (15% of the total catch) were documented. Of the 22 elasmobranch species observed, silky sharks, Carcharhinus falciformis, were numerically dominant (31.4% of the elasmobranch catch). The catch status of the animals (alive or dead) when the gear was retrieved varied widely depending on the species, with high mortalities seen for the commonly caught silky and night, C. signatus, sharks and low mortalities for rays (Dasyatidae and Mobulidae), blue, Prionace glauca; and tiger, Galeocerdo cuvier; sharks. Discard percentages also varied, ranging from low discards (27.6%) for shorfin mako, Isurus oxyrinchus, to high discards for blue (99.8%), tiger (98.5%), and rays (100%). Mean fork lengths indicated the majority of the observed bycatch - regardless of species - was immature, and significant quarterly variation in fork length was found for several species including silky; dusky, C. obscurus; night; scalloped hammerhead, Sphyrna lewini; oceanic whitetip, C. longimanus; and sandbar, C. plumbeus; sharks. While sex ratios overall were relatively even, blue, tiger, and scalloped hammerhead shark catches were heavily dominated by females. Bootstrap methods were used to generate yearly mean catch rates (catch per unit effort) and 95% confidence limits; catch rates were generally variable for most species, although regression analysis indicated significant trends for night, oceanic whitetip, and sandbar sharks. Analysis of variance indicated significant catch rate differences among quarters for silky, dusky, night, blue, oceanic whitetip, sandbar, and shortfin mako sharks.
Abstract—From 2001 to 2006, 71
pop-up satellite archival tags (PSATs)
were deployed on five species of
pelagic shark (blue shark [Prionace
glauca]; shortfin mako [Isurus oxyrinchus];
silky shark [Carcharhinus
falciformis]; oceanic whitetip shark
[C. longimanus]; and bigeye thresher
[Alopias superciliosus]) in the central
Pacific Ocean to determine speciesspecific
movement patterns and survival
rates after release from longline
fishing gear. Only a single postrelease
mortality could be unequivocally documented:
a male blue shark which
succumbed seven days after release.
Meta-analysis of published reports
and the current study (n=78 reporting
PSATs) indicated that the summary
effect of postrelease mortality for blue
sharks was 15% (95% CI, 8.5–25.1%)
and suggested that catch-and-release
in longline fisheries can be a viable
management tool to protect parental
biomass in shark populations.
Pelagic sharks displayed species-specific
depth and temperature ranges,
although with significant individual
temporal and spatial variability in
vertical movement patterns, which
were also punctuated by stochastic
events (e.g., El Niño-Southern Oscillation).
Pelagic species can be separated
into three broad groups based
on daytime temperature preferences
by using the unweighted pair-group
method with arithmetic averaging
clustering on a Kolmogorov-Smirnov
Dmax distance matrix: 1) epipelagic
species (silky and oceanic whitetip
sharks), which spent >95% of their
time at temperatures within 2°C of
sea surface temperature; 2) mesopelagic-
I species (blue sharks and
shortfin makos, which spent 95% of
their time at temperatures from 9.7°
to 26.9°C and from 9.4° to 25.0°C,
respectively; and 3) mesopelagic-II
species (bigeye threshers), which
spent 95% of their time at temperatures
from 6.7° to 21.2°C. Distinct
thermal niche partitioning based on
body size and latitude was also evident
within epipelagic species.
ABSTRACT: Pop-up satellite archival tags (PSATs) are
used to chronicle or ‘archive’ the habitat preferences,
horizontal and vertical movements, fishery interaction,
and post-release mortality rates of a variety of pelagic
animals. Though PSATs are valuable research tools,
lower-than-expected reporting rates, early detachment,
and incomplete data return remain problematic.
These issues were quantified by analysis of reporting
rates, retention times (i.e. the time period PSATs re -
mained attached), and the quantity of depth, temperature,
and geolocation data returned from 731 PSAT
deployments on 19 species in the authors’ database
and 1433 PSAT deployments on 24 species taken from
53 published articles. The reporting rate of PSATs de -
ployed by the authors (0.79, 95% CI = 0.76 to 0.82) was
not significantly different from the reporting rate calculated
from published studies (0.76, 95% CI = 0.74 to
0.78). PSAT reporting rates were lowest in species
undertaking large (~1000 m) vertical excursions (logistic
regression, p = 0.006), and reporting rates have
increased significantly over time (p = 0.02), presumably
because of better PSAT design and construction.
Tag retention increased with depth range of the tag -
ged species and pop-off latitude (Cox proportional
hazards models, p < 0.001), suggesting that pressure
(and/or temperature), biofouling, and wound infection
at the insertion site of the PSAT’s anchoring device
influenced this parameter. The quantity of data re -
turned by Argos satellites was affected by tag production
year, programmed pop-up period, depth range,
and manufacturer. Species-specific reporting rates
were used to make recommendations for future PSAT
sampling designs.
1. There has been considerable debate over the past decade with respect to wildlife provisioning, especially resultant behavioural changes that may impact the ecological function of an apex predator. The controversy is exemplified by the shark diving industry, where major criticisms based on inference, anecdote and opinion stem from concerns of potential behaviourally mediated ecosystem effects because of ecotourism provisioning (aka‘chumming’ or feeding).
2. There is a general lack of empirical evidence to refute or support associated claims. The few studies that have investigated the behavioural impacts of shark provisioning ecotourism have generated conflicting conclusions, where the confidence in such results may suffer from a narrow spatial and temporal focus given the highly mobile nature of these predators. There is need for studies that examine the potential behavioural consequences of provisioning over ecologically relevant spatial and temporal scales.
3. To advance this debate, we conducted the first satellite telemetry study and movement analysis to explicitly examine the long-range migrations and habitat utilization of tiger sharks (Galeocerdo cuvier) originating in the Bahamas and Florida, two areas that differ significantly with regards to the presence/absence of provisioning ecotourism.
4. Satellite telemetry data rejected the behaviourally mediated effects of provisioning ecotourism at large spatial and temporal scales. In contrast, to the restricted activity space and movement that were hypothesized, geolocation data evidenced previously unknown long-distance migrations and habitat use for both tiger shark populations closely associated with areas of high biological productivity in the Gulf Stream and subtropical western Atlantic Ocean. We speculate that these areas are likely critically important for G. cuvier feeding forays and parturition.
5. We concluded that, in the light of potential conservation and public awareness benefits of ecotourism provisioning, this practice should not be dismissed out of hand by managers. Given the pressing need for improved understanding of the functional ecology of apex predators relative to human disturbance, empirical studies of different species sensitivities to disturbance should be used to guide best-practice ecotourism policies that maximize conservation goals.
Sharks, turtles, billfish, and marine mammals are frequently caught accidentally in commercial fisheries. Although conservationists and fisheries managers encourage the release of these nontarget species, the long-term outcome of released animals is uncertain. Using blue sharks Prionace glauca, we developed a model to predict the long-term survival of released animals based on analysis of small blood samples. About 5% of the sharks were landed in obviously poor condition (lethargic and unresponsive to handling); these moribund sharks were sampled and euthanized. A subset of the remaining sharks was sampled and tagged with pop-up satellite archival tags (PSATs). Each of the PSATs that reported data (11 tags) showed that the sharks roamed at sea for at least 3 weeks postrelease. Five variables differentiated moribund sharks from survivors: Plasma Mg (moribund, 1.57 ± 0.08 mM; survivor, 0.98 ± 0.05 mM; P < 0.00001), plasma lactate (moribund, 27.7 ± 4.1 mM; survivor, 5.80 ± 2.96 mM; P < 0.001), erythrocyte heat shock protein 70 (Hsp70) mRNA (relative levels: Moribund, 3.96 ± 0.53; survivor, 1.00 ± 0.29; P < 0.005), plasma Ca (moribund, 3.70 ± 0.14 mM; survivor, 3.13 ± 0.11; P < 0.005), and plasma K (moribund, 7.01 ± 0.66 mM; survivor, 5.12 ± 0.44 mM; P < 0.05). These analyses were used to develop logistic regression models that could “predict” the long-term survival of captured sharks, including a larger group of sharks that we sampled but did not tag. The best logistic model, which incorporated Mg and lactate, successfully categorized 95% of fish of known outcome (19 of 20). These analyses suggest that sharks landed in an apparently healthy condition are likely to survive long term if released (95% survival based on biochemical analyses; 100% based on PSATs).
Declines in shark populations have sparked researchers and fishery managers to investigate more prudent approaches to the conservation of these fish. As managers strive to improve data collection for stock assessment, fisheries-independent surveys have expanded to include data-deficient areas such as coastal regions. To that end, a catch series from a nearshore survey off Alabama was combined with data from a concurrent offshore survey with identical methodology to examine the depth use of sharks across the continental shelf (2–366 m). The combined data set contained 22 species of sharks collected from 1995 to 2008: 21 species in the offshore data set (1995–2008) and 12 species in the nearshore data set (2006–2008). Depth was a significant factor determining species' distributions, primarily for Atlantic sharpnose Rhizoprionodon terraenovae, blacknose Carcharhinus acronotus, and blacktip C. limbatus sharks. Blacknose sharks had the highest catch per unit effort (CPUE) in the middepth stratum (10–30 m), blacktip sharks had consistently higher CPUE in the shallow depth stratum (
SUMMARY 1. Salt-water crocodiles, Crocodylus porosus Schneider, were catheter- ized and Po2, Pco2, pH and lactate concentration ((lactate)) were measured in arterial blood during rest and after forced exhaustive activity at 30°C. 2. Gas exchange ratio (R), calculated from blood Po2 and Pco2, decreased from about 1-0 to 0-3 during resting voluntary breath-holding and indicated CO2 sequestration in the body fluids. The mean value for R in undisturbed animals was 0-6, which substantiates the hypothesis that some CO2 excretion is extrapulmonary. 3. In vitro buffer value of true plasma was —23-5 +1-9 mmol HCO3~ 1~' pH" 1. In vivo buffer value, determined by short-term self titration with metabolic CO 2, was —12-2 + 4-7mmolHCO3~ I" 1 pH" 1. 4. Exhaustive activity for 5 min in laboratory animals resulted in pronounced metabolic lactacidosis: pH decreased approximately from 7-43 to 7-11 while lactate concentration increased from 1-2 to 20—30 mmoll" 1. The acidosis was reduced by respiratory compensation during the first hour of recovery and by metabolic adjustments that were practically complete after the third hour. Greater acidosis (pH down to 64) in larger field-captured animals was resolved over a longer period. 5. During recovery, lactate and proton fluxes between the blood and other tissue were uncoupled. 6. The virtual absence of the fixed-acid Bohr effect in C. porosus blood is adaptive in large individuals because it facilitates continued O2 uptake from the lung into blood which may be acidified by as much as 1 pH unit as a result of physical activity.
Between 1983 and 2004, nearly 12 000 shortf in mako (Isurus oxyrinchus), common thresher (Alopias vulpinus) and blue (Prionace glauca) sharks were tagged in the Southern California Bight; however, only 1.97% of these have been returned. One possible reason for this low return rate could be post-release mortality caused by capture stress from the experimental longline. Plasma catecholamine levels were analysed to evaluate stress levels in longline-captured, rod-and-reel-captured and unstressed docile sharks. The mean catecholamine values determined for the three tag–release species ranged from 6539 to 22 079 pg mL–1. The level of adrenaline found in moribund I. oxyrinchus (94 807 pg mL–1) was much higher than in either P. glauca (46 845 pg mL–1) or A. vulpinus (36 890 pg mL–1). In contrast, blood obtained from sharks that were landed within minutes had lower catecholamine values (P. glauca, 889 and 1347 pg mL–1; I. oxyrinchus, 2960 and 3946 pg mL–1, adrenaline and noradrenaline respectively). Among the nine I. oxyrinchus specimens that were recaptured long after their longline capture and release, the highest adrenaline level measured just before release was 33 352 pg mL–1. Because these mako sharks survived sufficiently long to be recaptured, their time-of-release catecholamine levels provide a conservative estimate of ~80% viability on the longline-captured and released population.
Blue sharks Prionace glauca are the most frequently discarded fish species during com- mercial pelagic longline fishing operations worldwide, yet their post-release mortality rate has never been measured. A generalized linear model of 12 404 blue sharks observed during the Canadian Atlantic pelagic longline swordfishery suggested a hooking mortality of 12 to 13%, yet scientific examination of 902 of these sharks indicated that hooking mortality was actually higher. A random sample of 40 of these blue sharks were tagged with satellite pop-up archival transmission (PAT) tags, then monitored for periods of up to 6 mo after release. All of the surviving sharks exhibited a depth- holding recovery behaviour for a period of 2 to 7 d after release. All healthy sharks survived, while 33% of those that were badly injured or gut hooked subsequently died. Overall blue shark bycatch mortality in the pelagic longline fishery was estimated at 35%, while the estimated discard mortality for sharks that were released alive was 19%. Survival time models indicated that 95% of the mortal- ity occurred within 11 d of release, indicative of death by trauma rather than starvation. The annual blue shark catch in the North Atlantic was estimated at about 84 000 t, of which 57 000 t is discarded. A preliminary estimate of 20 000 t of annual dead discards for North Atlantic blue sharks is similar to that of the reported nominal catch, and could substantially change the perception of population health if incorporated into a population-level stock assessment.
Anthropogenic climate change is already apparent and will have significant, ongoing impacts on Australian fishes and their habitats. Even with immediate actions to reduce greenhouse gases, there will be sustained environmental changes. Therefore, it is necessary to consider appropriate adaptations to minimise detrimental impacts for both fishes and the human populations that utilise them. Climate change will have a range of direct effects on the physiology, fitness, and survivorship of Australia’s marine, estuarine and freshwater fishes, but also indirect effects via habitat degradation and changes to ecosystems. Effects will differ across populations, species and ecosystems, with some impacts being complex and causing unexpected outcomes. The range of adaptation options and necessary levels of intervention to maintain populations and ecosystem function will largely depend on the vulnerability of species and habitats. Climate change will also have an impact on people who depend on fishes for food or livelihoods; adapting to a new climate regime will mean trade-offs between biological assets and socioeconomic drivers. Models can be used to help predict trends and set priorities; however, they must be based on the best available science and data, and include fisheries, environmental, socioeconomic and political layers to support management actions for adaptation.
Sharks are subjected to extensive commercial and recreational fisheries worldwide. Current management, which imposes bag limits, minimum sizes, and quotas, mandates the release of large numbers of sharks each year, but little is known of post-release behavior and survivorship. Using animal-borne imaging technology, we examined the effects of handline capture on post-release behavior of six grey reef sharks, Carcharhinus amblyrhynchos, at Johnston Atoll (Central Pacific) as it relates to physical trauma and physiological stress induced by capture. To quantify the extent of physical trauma, 25 grey reef sharks (including these six), ranging from 56-135 cm fork length, were examined for evidence of external tissue damage after 2.0-12.8 minutes of handline capture. In addition, these fish were blood sampled to quantify relative changes in acid-base biochemistry. Although blood lactate increased and blood bicarbonate decreased significantly relative to the duration of the capture event, blood pH did not drop significantly and there was no evidence of respiratory or metabolic acidoses. Post-release behavior, as evidenced by animal-borne imaging, included group (n=3) and solitary (n=2) activities that had been previously described in this species. A single shark exhibited aberrant behavior, which included a two-minute period of disorientation, lack of movement, and loss of equilibrium; this behavior was attributed to extensive physical trauma associated with hook damage. When coupled with quantified information relative to the capture event, we found that animal-borne imaging is a useful tool for collecting direct observations of post-release behavior in sharks so that fishery managers and researchers can better assess the impacts of various capture techniques.
Exploitation of fishery resources has become a major conservation issue on a global scale. Commercial fisheries have been
repeatedly blamed for the worldwide declines in fish populations. However, we contend that the recreational fishing sector
also has the potential to negatively affect fish and fisheries. Here we present evidence to show that both recreational and
commercial fishing sectors deserve consideration as contributors to the exploitation of fish in marine and inland waters.
The lack of global monitoring and compiling of statistics on recreational fishing participation, harvest, and catch-and-release
has retarded our ability to understand the magnitude of this fishing sector. Using data from Canada, we estimate that the
potential contribution of recreational fish harvest around the world may represent approximately 12 percent of the global
fish harvest. Failure to recognize the potential contribution of recreational fishing to fishery declines, environmental degradation,
and ecosystem alterations places ecologically and economically important resources at risk. Elevating recreational fishing
to a global conservation concern would facilitate the development of strategies to increase the sustainability of this activity.
Predators can impact ecosystems through trophic cascades such that differential patterns in habitat use can lead to spatiotemporal variation in top down forcing on community dynamics. Thus, improved understanding of predator movements is important for evaluating the potential ecosystem effects of their declines.
We satellite-tagged an apex predator (bull sharks, Carcharhinus leucas) and a sympatric mesopredator (Atlantic tarpon, Megalops atlanticus) in southern Florida waters to describe their habitat use, abundance and movement patterns. We asked four questions: (1) How do the seasonal abundance patterns of bull sharks and tarpon compare? (2) How do the movement patterns of bull sharks and tarpon compare, and what proportion of time do their respective primary ranges overlap? (3) Do tarpon movement patterns (e.g., straight versus convoluted paths) and/or their rates of movement (ROM) differ in areas of low versus high bull shark abundance? and (4) Can any general conclusions be reached concerning whether tarpon may mitigate risk of predation by sharks when they are in areas of high bull shark abundance?
Despite similarities in diet, bull sharks and tarpon showed little overlap in habitat use. Bull shark abundance was high year-round, but peaked in winter; while tarpon abundance and fishery catches were highest in late spring. However, presence of the largest sharks (>230 cm) coincided with peak tarpon abundance. When moving over deep open waters (areas of high shark abundance and high food availability) tarpon maintained relatively high ROM in directed lines until reaching shallow structurally-complex areas. At such locations, tarpon exhibited slow tortuous movements over relatively long time periods indicative of foraging. Tarpon periodically concentrated up rivers, where tracked bull sharks were absent. We propose that tarpon trade-off energetic costs of both food assimilation and osmoregulation to reduce predation risk by bull sharks.
Catch-and-release recreational angling has become very popular as a conservation strategy and as a fisheries management tool for a diverse array of fishes. Implicit in catch-and-release angling strategies is the assumption that fish experience low mortality and minimal sub-lethal effects. Despite the importance of this premise, research on this topic has focused on several popular North American sportfish, with negligible efforts directed towards understanding catch-and-release angling effects on alternative fish species. Here, we summarise the existing literature to develop five general trends that could be adopted for species for which no data are currently available: (1) minimise angling duration, (2) minimise air exposure, (3) avoid angling during extremes in water temperature, (4) use barbless hooks and artificial lures/flies, and (5) refrain from angling fish during the reproductive period. These generalities provide some level of protection to all species, but do have limitations. Therefore, we argue that a goal of conservation science and fisheries management should be the creation of species-specific guidelines for catch-and-release. These guidelines would take into account the inter-specific diversity of fishes and variation in fishing techniques. As recreational angling continues to grow in popularity, expanding to many developing countries, and targeting alternative species, it is important that reasonable data appropriate for specific fish and fisheries are available. The sustainable use and conservation of recreational fishery resources will depend upon the development and dissemination of effective catch-and-release angling strategies based upon sound science to stakeholders around the world.
Introduction Despite the ecological significance of elasmobranchs as top-level predators in most marine ecosystems (Cortés, 1999), information on their energetics and metabolism is meager. Metabolism is an important component of an organism’s daily energy budget and may account for its greatest, yet most variable proportion (Lowe, 2001). It was hypothesized that sharks had lower metabolic rates than comparable teleosts because most of the original work on the metabolic rate of sharks focused on relatively inactive, cooler-water sharks such as spotted dogfish, Scyliorhinus canicula (Piiper and Schumann, 1967; Metcalf and Butler, 1984) and spiny dogfish, Squalus acanthias (Brett and Blackburn, 1978). Over time, better techniques have evolved that allow study of more active elasmobranch species that were typically considered difficult to work with in captivity. These advances in technology have expanded our knowledge of ecology, activity level, morphology, cellular physiology, and kinematics of elasmobranchs that exhibit a wide range of lifestyles, indicating that elasmobranchs have metabolic rates comparable to teleost fishes of similar size and lifestyle.
Comparisons of survival or recovery rates from different time periods or geographic regions may be difficult to accomplish using the Z-tests suggested by Brownie et al. (1985). We propose a general Chisquare statistic that addresses an unambiguous null hypothesis of homogeneity among several survival or recovery rates. With this statistic, specific hypotheses of differences in rates can be simultaneously tested using contrasts. If necessary, a posteriori multiple comparisons can also be conducted that incorporate an adjustment for Type I error.
Since the sinking of the USS Indianapolis (CA-35) and associated shark attacks in 1945, the quest to find an effective shark repellent has been endless. Early efforts were focused on finding a shark repellent which would minimize the probability of a shark attack. However, studies illustrate that shark populations are drastically declining which has led to calls for effective management policies and practices to reduce both directed catch and bycatch of various shark species. With increased need for shark conservation, the focus has shifted to protecting sharks from harmful anthropogenic pressures, such as fishing gear and beach nets. Current shark repellent technologies which aim to minimize elasmobranch mortality in fishing gears include: permanent magnets, electropositive metal (EPM) alloys, and semiochemicals. This paper will review present electrosensory and semiochemical shark repellents, the mechanisms of elasmobranch (e.g. shark, skate and ray) detection and repellency, species-specificity in elasmobranch response to the stimuli, and environmental and biological conditions which may influence repellent success. Future research to enhance our knowledge on electrosensory repellents and to improve the success of repellent implementation and application will be discussed.
Over the past 20 years, there has been a dramatic increase in the use of physiological tools and experimental approaches for the study of the biological consequences of catch‐and‐release angling practices for fishes. Beyond simply documenting problems, physiological data are also being used to test and refine different strategies for handling fish such that stress is minimised and survival probability maximised, and in some cases, even for assessing and facilitating recovery post‐release. The inherent sensitivity of physiological processes means that nearly every study conducted has found some level of – unavoidable – physiological disturbance arising from recreational capture and subsequent release. An underlying tenet of catch‐and‐release studies that incorporate physiological tools is that a link exists between physiological status and fitness. In reality, finding such relationships has been elusive, with further extensions of individual‐level impacts to fish populations even more dubious. A focus of this article is to describe some of the challenges related to experimental design and interpretation that arise when using physiological tools for the study of the biological consequences of catch‐and‐release angling. Means of overcoming these challenges and the extrapolation of physiological data from individuals to the population level are discussed. The argument is presented that even if it is difficult to demonstrate strong links to mortality or other fitness measures, let alone population‐level impacts of catch‐and‐release, there remains merit in using physiological tools as objective indicators of fish welfare, which is an increasing concern in recreational fisheries. The overarching objective of this paper is to provide a balanced critique of the use of physiological approaches in catch‐and‐release science and of their role in providing meaningful information for anglers and managers.
Bonefish (Albula spp.) are a group of species targeted by recreational anglers in shallow tropical and sub-tropical seas worldwide. Although bonefish angling is almost entirely catch-and-release, mortality can occur because the stress associated with angling and handling causes locomotory impairment that promotes post-release predation. We used tri-axial accelerometer loggers to compare the locomotor activity and behavior of bonefish exposed to angling-related stressors and immediately released (n = 10, 39.9 ± 1.1. cm FL), to those retained in a recovery bag for 15. min prior to release (n = 10, 39.6 ± 1.0. cm FL) in a tidal creek in Eleuthera, The Bahamas. We also validated the use of reflex action mortality predictors (RAMP) as an impairment index for evaluating bonefish condition upon release. Following release, bonefish were visually tracked for 30. min with floats to evaluate short-term survival, after which the accelerometer was retrieved. Bonefish held in recovery bags exhibited significantly less locomotory impairment immediately post-release, and higher maximum tail beat frequencies and amplitudes up to 15. min post-release, which was likely due to the time spent in the recovery bag. Bonefish in the recovery bag treatment also spent more time resting in possible refuge areas, which may facilitate further recovery and avoidance from predation. RAMP provided a gradient of impairment scores that were correlated with stressor duration. Retaining bonefish in recovery bags improved swimming abilities during the critical time period where the majority of post-release predation occurs, and one fish that was not placed in the recovery bag was preyed upon during the monitoring period. Further testing is needed to determine if the locomotory and behavioral benefits of retaining bonefish in recovery bags translate into improved survival from predation in more predator rich environments.
We provide pilot data from a satellite-tracked great hammerhead shark Sphyrna mokarran in the Atlantic, representing the first such data on this species in the literature. The 250 cm shark was tagged off the coast of the middle-Florida Keys (USA) and transmitted for 62 d. During this time it migrated a minimum distance of ~1200 km northeast from the coast of Florida, into pelagic international waters of the Northwest Atlantic. When compared to the primary literature, this migration represented a northeasterly range extension for this species off the continental slope in the Atlantic. The significance of this range extension is discussed in terms of the vulnerability of S. mokarran to target and non-target fisheries.
Few studies have examined the effects of fisheries capture on wild fish, particularly in the context of evaluating the sustainability of capture and release methods for Pacific salmon (Oncorhynchus spp.) during upriver migration. This study examined the physiological condition, post-release behaviour and survival of adult migrating sockeye salmon (O. nerka) in the Fraser River, British Columbia, Canada. Fish were captured by either beach seine or angling and released immediately, or were captured by angling and released following a 24-h recovery period in a net pen. Before release, all salmon were biopsied or tagged with radio telemetry transmitters. Capture by either angling or beach seine with immediate release resulted in >95% survival 24h after release, whereas net pen recovery after angling resulted in ∼80% survival. This differential in survival was similarly expressed in the percentage of released fish reaching natal sub-watersheds, with 52.2% and 36.3% of fish immediately released by beach seine and angling reaching natal sub-watersheds, respectively, compared with 2.9% of fish released after angling and net pen recovery. Blood plasma stress indices reflected the 10-fold difference in survival, with a ∼4-fold higher plasma cortisol, a ∼2-fold higher plasma glucose and significantly depressed plasma ions and osmolality relative to fish sampled upon capture. Plasma lactate did not differ among groups. Collectively, these results suggest that a 24h recovery in net pen following angling failed to promote post-release survival experienced with immediate release after angling or beach seining.
The primary gear type used to harvest coastal sharks in the U.S. Atlantic shark fishery is bottom longline. Recent stock assessments have found several species of coastal sharks in U.S. Atlantic Ocean waters have declined from 60% to 80% of virgin levels. To aid in stock rebuilding, alternative gear restriction measures such as reduced soak time, restrictions on the length of gear, and fishing depth restrictions have been considered but not implemented. In order to evaluate the effectiveness of some of these management measures, controlled experiments were performed using hook timers and time depth recorders, assessing the factors affecting mortality during longline capture for the four most abundant species that incurred at-vessel mortality: sandbar (Carcharhinus plumbeus), blacktip (Carcharhinus limbatus), bull (Carcharhinus leucas), and blacknose (Carcharhinus acronotus). Our results indicate that as hook time and shark size increased mortality rates for the sandbar and blacktip sharks increased. Predicted models indicated mortality rates increased steadily for the three species but appeared to increase the most after 10, 6, and 1h on the hook for sandbar, blacktip and blacknose shark, respectively. Sandbar sharks larger than approximately 170cm FL are more susceptible to hooking mortality. Blacknose shark mortality rates increased as hook time increased but bull shark mortality rates were not affected by any factor. The probability of a hook being bitten increased the most between 5 and 12h after the fishing gear had been set and the mean amount of time hooks were in the water prior to being bitten was 4, 5 and 9h for sandbar and blacknose sharks, blacktip, and bull sharks, respectively. A significant difference was found between these means for sandbar and bull sharks and between blacknose and bull sharks. Shark species were commonly caught at different temperature and depth ranges. These results could be used by fisheries management to implement restrictions of fishing depth and soak time to aid in the recovery of coastal sharks species.
Animal-attached remote sensing, or bio-logging, refers to the deployment of autonomous recording tags on free-living animals, so that multiple variables can be monitored at rates of many times per second, thereby generating millions of data points over periods ranging from hours to years. Rapid advances in technology are allowing scientists to use data-recording units to acquire huge, quantitative datasets of behavior from animals moving freely in their natural environment. In other words, scientists can examine wild animals in the field, behaving normally, with the same rigor that is normally used in the laboratory. The flexibility of such recording systems means that bio-logging science operates at the interface of several biological disciplines, looking at a wide array of aquatic, airborne, and terrestrial species, monitoring not only the physical characteristics of the environment, but also the animal's reactions to it. This approach is critically important in an era when global change threatens the survival of species and where habitat loss is leading to widespread extinctions.
Most research on catch-and-release (C&R) in recreational fishing has been conducted from a disciplinary angle focusing on the biological sciences and the study of hooking mortality after release. This hampers understanding of the complex and multifaceted nature of C&R. In the present synopsis, we develop an integrative perspective on C&R by drawing on historical, philosophical, socio-psychological, biological, and managerial insights and perspectives. Such a perspective is helpful for a variety of reasons, such as 1) improving the science supporting successful fisheries management and conservation, 2) facilitating dialogue between managers, anglers, and other stakeholders, 3) minimizing conflict potentials, and 4) paving the path toward sustainable recreational fisheries management. The present work highlights the array of cultural, institutional, psychological, and biological factors and dimensions involved in C&R. Progress toward successful treatment of C&R might be enhanced by acknowledging the complexity inherent in C&R recreational fishing.
Handling in fish induces perturbations of various biological parameters which have been investigated or reviewed in an attempt to analyse and quantify the resulting stress. Endocrine changes, being early consequences of stress, are referred to as primary effects. Original data obtained on coho (Oncorhynchus kisutch), sockeye (O. nerka), and chinook (O. tshawytscha) salmon show that all types of stress result in an increase in circulating catecholamines, mainly adrenaline. There is no quantitative difference in response intensity between the species studied but large individual variations exist. In mature male coho salmon, struggling and hypoxia also resulted in an increase of plasmatic corticosteroids. Secondary effects occur as a result of these endocrine changes. Metabolic disturbances include a pronounced increase in blood glucose, and either a decrease or an increase of plasmatic free fatty acid (FFA) according to the species. These metabolic disturbances brought about by stress of short duration are shown to be of relatively long duration. Recent advances in the understanding of osmoregulatory processes show that the action of catecholamines on gill permeability may explain the stress-induced water imbibition of fish in fresh water and the dehydration of fish in seawater. Beyond some practical considerations, the results reported open up the possibility for genetic selection of varieties of high or low response to stress.
Summary In fish, exhaustive exercise stress differs from steady-state aerobic exercise in causing (1) a depletion of glycogen, creatine phosphate (CP) and ATP reserves and an accumulation of lactate and metabolic acid (H^) in white muscle; (2) blood respiratory and metabolic acidoses {Pcch an d Hm elevations, respectively); (3) marked ionic and fluid volume disturbances; and (4) a surge in plasma catechol- amines. During recovery, the smaller fast component (20%) of excess post- exercise oxygen consumption (EPOC) is explained by CP and ATP resynthesis and aerobic demands, but the larger slow component (80%) is considerably greater than the cost of lactate clearance and glycogen resynthesis. Ionic and H2O shifts may contribute significantly to EPOC; net fluxes are greatest between extracellular (ECF) and intracellular fluid (ICF) compartments, with smaller disturbances at the kidney (increased filtration, reabsorption and excretion) and gills (passive ion losses and H2O uptake). Modulation of branchial Na + and CP exchange is important in the temporary storage of Hj in the environment during recovery. Movements of lactate and H+ from ICF to ECF are dissociated processes; the major portions of both are retained in the white muscle and are probably cleared by oxidation and/or glycogen resynthesis in situ. Elevated catecholamine levels are implicated in many of these responses and serve to protect metabolic processes against acid-base disturbances, but do not appear to contribute to EPOC directly. Catecholamines also cause an elevation in blood Pco2 by a mechanism linked to the j3-adrenergic activation of red blood cell Na + /H + exchange that protects O2 transport. The compound blood addosis stimulates ventilation to meet the demands of EPOC.
Physiological effects of physical conditioning to water current were studied on three groups of -year-old rainbow trout, Salmo gairdneri, acclimated to 4 C. Group one (control) was raised in still water. Groups two and three were conditioned to water velocities of 20 cm/sec and 40 cm/sec, respectively, for 16 days before sampling. Muscle and plasma samples were collected before exercise and four times during subjection to 15 min of forced swimming at 53.4 cm/sec and eight times during a 24-hr recovery period. Conditioning significantly delayed the point of fatigue during forced exercise: the unconditioned fish were fatigued after about 5 min swimming, group two after about 10 min swimming, and group three at about 15 min.Physically conditioned trout showed significantly higher muscle and plasma lactate levels when fatigued, and more rapid removal of lactate from muscle and plasma during recovery from fatigue, than unconditioned trout. Exercise resulted in parallel oscillating concentration fluctuations of tissue phosphate and significant increases in concentrations of plasma phosphate in both conditioned and unconditioned fish. Plasma glucose showed no significant change during exercise but rose slightly during the recovery of all groups.
Between 1978 and 1993, 209 great hammerhead sharks Sphyrna mokarran were caught in the shark nets which protect the swimming beaches of KwaZulu-Natal. This species constituted 0,97% of the total shark catch, with a mean annual catch of 13. Catch rates showed a significant decline during the period under review, from 0,66 to 0,09 sharks·km-net−1·year−1. Most sharks were caught in the north of the netted region between January and May. Catches at Mzamba, the southern extremity of the netted region, represent the southernmost records of this species on the east African coast. The males ranged in size from 106 cm precaudal length (18 kg) to 264 cm (220 kg) and females from 140 cm (35 kg) to 326 cm (400 kg). Males matured at about 217 cm and females at 237 cm. Very few sharks were found in mating condition. Elasmobranchs were found in 82% of non-empty stomachs. There was a high incidence of stingrays (Dasyatidae), guitarfish (Rhinobatidae) and other bottom-dwelling fish in the diet.
Generalized linear models were used to derive indices of abundance for blue (Prionace glauca) and shortfin mako (Isurus oxyrinchus) sharks based on two components of the US Atlantic recreational fishery: (1) the private and charter boat recreational anglers covered by the Marine Recreational Fisheries Statistics Survey (MRFSS, 1981-2002) of the National Marine Fisheries Service and (2) Massachusetts shark tournaments (1991-2004). From the MRFSS data, blue shark catch per unit effort (CPUE) showed different trends for different regions, seasons, and fishing modes, implying that CPUE is not tracking blue shark abundance. Mako shark CPUE differed by mode for private versus charter boats, and showed no trend in either boat type. From the Massachusetts tournament data, blue shark CPUE showed different trends north and south of Cape Cod. Mako shark CPUE declined in the late 1990s in Massachusetts tournaments, then increased again in 2002.
While government fisheries agencies have not documented the recreational fisheries for pelagic sharks in most countries, information exists in the records of fishing clubs, cooperative tagging programs, and the International Game Fish Association. Countries with signifi- cant pelagic shark recreational fisheries include Australia, New Zealand, the United States, and the United Kingdom. Some recreational pelagic shark fishing also occurs in Ireland, Italy, the Azores, Mauritius, South Africa, the Caribbean, and Mexico. Most pelagic shark game fishing is now catch-and-release, and the total mortality caused by recreational fisheries has been declining since the 1980s. The most commonly caught pelagic sharks are blue (Prionace glauca), shortfin mako (Isurus oxyrinchus), porbeagle (Lamna nasus), and thresher sharks (Alopias spp.).
Our understanding of predator-prey interactions in fishes has been influenced largely by research assuming that the condition of the participants is normal. However, fish populations today often reside in anthropogenically altered environments and are subjected to many kinds of stressors, which may reduce their ecological performance by adversely affecting their morphology, physiology, or behaviour. One consequence is that either the predator or prey, or both, may be in a substandard condition at the time of an interaction. We reviewed the literature on predator-prey interactions in fishes where substandard prey were used as experimental groups. Although most of this research indicates that such prey are significantly more vulnerable to predation, prey condition has rarely been considered in ecological theory regarding predator-prey interactions. The causal mechanisms for increased vulnerability of substandard prey to predation include a failure to detect predators, lapses in decision-making, poor fast-start performance, inability to shoal effectively, and increased prey conspicuousness. Despite some problems associated with empirical predator-prey studies using substandard prey, their results can have theoretical and applied uses, such as in ecological modelling or justification of corrective measures to be implemented in the wild. There is a need for more corroborative field experimentation, a better understanding of the causal mechanisms behind differential predation, and increased incorporation of prey condition into the research of predator-prey modellers and theoreticians. If the concept of prey condition is considered in predator-prey interactions, our understanding of how such interactions influence the structure and dynamics of fish communities is likely to change, which should prove beneficial to aquatic ecosystems.
The common thresher shark (Alopias vulpinus) is the focus of a popular southern California recreational fishery that typically captures individuals by hooking them in the caudal fin. This technique reduces the ability for forward locomotion and the capacity for ram ventilation. This study assessed the post-capture survivorship of tail-hooked adult and sub-adult common thresher sharks using pop-up satellite archival tags (PSATs) and quantified physiological indicators of capture stress in the blood. Survival of the acute effects of capture was determined from the depth and temperature records of 10-day PSAT deployments. Survivorship estimates were based on 19 common thresher sharks [160–221 cm fork length (FL); ∼67–151 kg] captured in southern California from 2007 to 2009 using recreational stand-up tackle (36 kg). Five mortalities were observed over the course of the study resulting in an overall post-release mortality estimate of 26%. All mortalities occurred in large individuals (≥180 cm FL) with fight times ≥85 min. The archived depth and temperature data from surviving sharks resembled those of previous common thresher movement studies with a diel depth distribution predominantly within the uniformed temperature surface layer. Capture induced stress parameters measured from the blood of eight additional common thresher sharks that were not tagged revealed plasma lactate and hematocrit levels that were significantly elevated with increased fight time. Similarly, all thresher sharks showed heightened heat shock protein 70 (hsp 70) values relative to those obtained from blood that was allowed to recover in vitro for 24 h. Collectively, our findings indicate that large tail-hooked common thresher sharks with prolonged fight times (≥85 min) exhibit a heightened stress response which may contribute to an increased mortality rate. These results suggest that for larger individuals the current caudal-based capture methods used in the California recreational fishery may not be suitable for an effective catch-and-release based conservation strategy.
1. Effective management of fish and wildlife populations benefits from an understanding of the effects of stressors on individual physiology. While physiological knowledge can provide a mechanistic understanding of organismal responses, its applied utility is limited because it cannot easily be used by stakeholders.
2. Reflex action mortality predictors (RAMP) is a method that involves checking for the presence or absence of natural animal reflexes to generate a condition (RAMP) score in response to stressors and to predict fate. The method has previously been validated with fishes in artificial laboratory- and field-based holding studies as a responsive measure of fisheries capture stress and a predictor of delayed mortality, but has not been evaluated in the wild.
3. We used radio telemetry to monitor migration success of 50 endangered coho salmon Oncorhynchus kisutch following incidental capture in an aboriginal beach seine fishery in the lower Fraser River (Canada). RAMP was used to measure the condition of fish at release and to predict migration success following capture. Biopsy of an additional 43 coho profiled physiological condition at time of release.
4. Individuals with greater reflex impairment (higher RAMP scores) at release experienced significantly higher rates of migration failure. RAMP scores were also significantly correlated with fishery handling time. Plasma variables showed that captured coho had experienced physiological stress characteristic of exhaustive exercise and hypoxia, with significantly elevated cortisol and lactate values for fish entangled longer in fishing gear.
5. Synthesis and applications. This is the first validation of RAMP in a wild setting. Based on our findings, fishers could use the method and make adjustments in fishing behaviour in real-time to improve fish condition and reduce the mortality of bycatch, and conservation practitioners could monitor animal condition and identify problems that deserve management attention. RAMP is an easy, rapid and inexpensive approach to predicting mortality and measuring vitality and performed better than traditional physiological tools that cannot easily be used by stakeholders.
a b s t r a c t The abundance of Atlantic bluefin tuna has been severely reduced since the advent of industrial fishing. A recreational catch-and-release fishery is currently being developed to target bluefin tuna in the southern Gulf of St. Lawrence, off the coast of Prince Edward Island, Canada. To evaluate the sustainability of this fishery, it is necessary to quantify post-release mortality for use in management models. Using pop-up archival satellite tags, we estimated the post-release mortality rate of bluefin tuna captured and released in an experimental recreational fishery. Fish were captured using bait on circle hooks and all fish were hooked in the jaw. Fish were released without being brought onboard the boat. Tags reported from 2 to 246 days post release. Two of 59 bluefin tuna died after catch-and-release yielding a mortality rate of 3.4% (95% C.I. = 0.8% < u < 12.6%). Four tags failed to report. Alternate estimates of the rate or mortality that included an incidental mortality (5.1%; 95% C.I. = 1.6% < u < 14.4%) and removal of the four tags that did not report from the sample (5.6%; 95% C.I. = 1.8% < u < 15.6%) were calculated. The range of fight times was 6–79 min (mean of 33 min; SD of 21 min). These data provide the first mortality estimates for angled and released bluefin tuna and will enable managers to evaluate the potential for developing a catch-and-release fishery in the southern Gulf of St. Lawrence.
While the impacts of high exploitation on fish populations and aquatic ecosystems are well-documented for commercial fishing, particularly in the marine environment, the potential biological impacts of angling received less attention. This paper discusses angling patterns within a framework of basic ecological and evolutionary literature and examines potential biological impacts of angling by focus-ing on study results associated with high exploitation rates and pronounced selective exploitation. The impacts range from impacts occurring directly on the exploited species (truncation of the natural age and size structure, depensatory mechanisms, loss of ge-netic variability, evolutionary changes), to those that occur on the aquatic ecosystem (changes in trophic cascades, trait-mediated effects). As a third category, impacts re-lated to the angling activity per se are distinguished (habitat modifications, wildlife disturbance, nutrient inputs, loss of fishing gear). Although the main threats to fish often are localized outside recreational fisheries, there is growing evidence that angling and angling associated activities can lead to a decline of fish populations and affect aquatic ecosystems in various ways provided that the degree of the fishing mortality is high and the selective exploitation is intensive. In conclusion, management implications for sustainable recreational fisheries and areas for future research are outlined.
We performed a quantitative review to evaluate circle hook use in recreational and commercial hook-and-line fisheries that interact with billfishes (Family: Istiophoridae). Specifically, we scrutinized the findings of 11 recent empirical studies that reported, on a species-specific basis, side-by-side measures of circle vs. J-hook fishing performance: catch, mortality, deep-hooking and bleeding rates. Of the 30 total comparisons extracted from the literature that satisfied our inclusion criteria, 13 indicated significant differences between hook types for the specific metric compared. No study reported significant billfish catch rate differences between hook types. However, when significant differences between hook types were found, higher mortality rates and higher rates of deep-hooking and bleeding were associated with J-hooks relative to circle hooks. We conclude that empirical evidence is sufficient to promote circle hook use in almost all hook-and-line fishery sectors that typically interact with istiophorids. However, billfish conservation benefits will only be realized if fishers use unmodified circle hooks, commit to releasing live fish and take other appropriate measures which maximize post-release survival. While there may be fishing modes where circle hook effects are negative, for billfish conservation, we recommend managers grant exceptions to circle hook use only when experimental results support such a practice.
Fish stress and mortality can be significant problems in both capture and culture operations. In addition to inexpensive and real-time metrics, ones that are simple to use are also desirable for measuring fish stress and predicting mortality. Current methods to define stress rely on expensive, laboratory-based measurements of changes in fish pathology such as disease, necropsy and histology, in physiology such as plasma cortisol, lactate, glucose and ions and in complex behaviour determined from swimming, feeding and predator evasion. All of these methods are often not rigorously linked to fitness outcomes. An alternative is to observe reflex impairment as a direct sign of stress which can be easily and rapidly measured in free swimming or restrained fish responding to peripheral stimuli such as gravity, light, sound and touch. Reflex impairment is correlated with stress and mortality outcomes, eliminating the need for prolonged holding or monitoring of fish. A few examples of reflexes that may be impaired include orientation, startle responses, fin erection, body flex upon restraint, operculum and mouth clamping or gaping, gag response and vestibular–ocular response. Reflex impairment combines the effects of stressors and their interactions and is not dependent on fish size, motivation states and acclimation which make it a consistent sign of stress across a wide range of stressor types and fish ages. Use of reflex impairment to measure stress and predict mortality would significantly improve monitoring of fish health and welfare in many types of field operations such as commercial and recreational fishing, aquaculture, live transport, stock enhancement and tagging.
Catch-and-release (C&R) angling is widely practised by anglers and is a common fisheries management strategy or is a by-product of harvest regulations. Accordingly, there is a growing body of research that examines not only the mortality associated with C&R, but also the sublethal physiological and behavioural consequences. Biotelemetry offers a powerful means of remotely monitoring the behaviour, physiology and mortality of fish caught and released in their natural environment, but we contend that its usefulness is still underappreciated by scholars and managers. In this study, we review the applications of biotelemetry in C&R science, identify novel research directions, opportunities and challenges. There are now about 250 C&R studies but only one quarter of these utilize biotelemetry. In fact, almost all of the C&R studies that have used biotelemetry have been conducted within the last decade. We found that the majority of C&R telemetry studies used either radio or acoustic telemetry, while comparatively few studies have used satellite technologies. Most C&R biotelemetry studies have been used to assess mortality rates, behavioural impairments or to evaluate the effects of displacement on fish. A small fraction of studies (<8%) have used physiological sensors despite the fact that these tools are highly applicable to understanding the multiple sublethal consequences of C&R and are useful for providing mechanistic insights into endpoints such as death. We conclude that C&R science has the potential to benefit greatly from biotelemetry technology, particularly with respect to providing more robust short-term and delayed mortality estimates and adopting a more integrative and comparative approach to understanding the lethal and sublethal impacts of C&R. However, there are still a number of challenges including (i) the need for appropriate controls and methodological approaches, (ii) the need for accounting for tagging and handling stress and mortality, and (iii) the need for certainty in assessing mortality. However, the benefits associated with C&R biotelemetry outweigh its disadvantages and limitations and thereby offer C&R researchers a suite of new tools to enhance fisheries management and conservation.