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Killing for conservation: The need for alternatives to lethal sampling of apex predatory sharks
Abstract
Top oceanic predators, especially large predatory sharks (TOPS), appear to be experiencing varying degrees of population declines. Life history data (e.g. diet, reproductive status, age and growth, mortality) are critical for developing effective conservation strategies for TOPS. Presently, lethal sampling remains the most effective and accurate means of gathering these data. To meet such challenges, many scientists have utilized specimens obtained from recreational and commercial fisheries, but have needed to supplement those data with fishery-independent sampling. However, there is growing public and scientific debate as to whether lethal sampling of TOPS is justified for obtaining conservation data. Here we describe the development and use of non-lethal alternatives for collecting data on (1) trophodynamics; (2) maturity state and fecundity; and (3) growth and mortality rates necessary to enact conservation measures for threatened or even data-deficient TOPS.
... Given the generally imperilled state of many fish species globally, non-lethal research methodologies have become increasingly popular (Hammerschlag & Sulikowski 2011). These methodologies are even more pertinent for many largebodied fish taxa (i.e., fishes with body masses on the order of kilograms in adulthood), such as elasmobranchs (sharks, rays, and skates) and Acipenseriformes (paddlefishes and sturgeons). ...
... These methodologies are even more pertinent for many largebodied fish taxa (i.e., fishes with body masses on the order of kilograms in adulthood), such as elasmobranchs (sharks, rays, and skates) and Acipenseriformes (paddlefishes and sturgeons). Indeed, non-lethal methods for estimating condition for these fishes may improve our understanding of the energetics of current-day populations and allow for better non-lethal monitoring of these fishes under anthropogenic stressors now and in the future (Hammerschlag & Sulikowski 2011). ...
... Therefore, both GSI and HSI are good indicators of short-term and seasonal changes in condition related to energy stores, reproduction, and even the influence of environmental factors such as temperature or environmental contaminants (Hoffmayer et al., 2006: Hussey et al., 2009Lyons et al., 2017;Rizzo & Bazzoli 2019;Weideli et al., 2019). However, sampling to obtain GSI or HSI is lethal, and therefore not feasible for many species (Hammerschlag & Sulikowski 2011), and in many large-bodied fishes such as pelagic sharks, obtaining body mass can be logistically challenging, if possible, at all ). Alternatively, a body condition metric using the sum of spans and length has been developed ). ...
... Given the generally imperilled state of many fish species globally, nonlethal research methodologies have become increasingly popular (Hammerschlag & Sulikowski, 2011). Indeed, nonlethal methods for estimating condition for these fishes may improve our understanding of the energetics of current-day populations and allow for better nonlethal monitoring of these fishes under anthropogenic stressors now and in the future (Hammerschlag & Sulikowski, 2011). ...
... Given the generally imperilled state of many fish species globally, nonlethal research methodologies have become increasingly popular (Hammerschlag & Sulikowski, 2011). Indeed, nonlethal methods for estimating condition for these fishes may improve our understanding of the energetics of current-day populations and allow for better nonlethal monitoring of these fishes under anthropogenic stressors now and in the future (Hammerschlag & Sulikowski, 2011). Amongst the fishes, body condition is classically assessed using whole animal length and mass, and the simplest form of Fulton's seminal equation [K = (mass/length 3 ) Â 100], in which the cubed exponent is a scaling estimate (Fulton, 1904). ...
... Therefore, both GSI and HSI are good indicators of short-term and seasonal changes in condition related to energy stores, reproduction and even the influence of environmental factors such as temperature or environmental contaminants (Hoffmayer et al., 2006: Hussey et al., 2009Lyons et al., 2017;Rizzo & Bazzoli, 2019;Weideli et al., 2019). However, sampling to obtain GSI or HSI is lethal and therefore not feasible for many species (Hammerschlag & Sulikowski, 2011), and in many large-bodied fishes such as pelagic sharks, obtaining body mass can be logistically challenging, if possible at all . Alternatively, a body condition metric using the sum of spans and length has been developed . ...
Body condition is an important proxy for the overall health and energetic status of fishes. The classically used Fulton's condition factor requires length and mass measurements, but mass can be difficult to obtain in large species. Girth measurements can replace mass for wild pelagic sharks. However, girth‐calculated condition has not been validated against Fulton's condition factor intraspecifically, across ontogeny or reproduction, or in a controlled setting. We used the epaulette shark (Hemiscyllium ocellatum), because they are amenable to captive reproduction, to track fine‐scale body condition changes across life stages, oviparous reproduction and between condition indices. We measured four girths, total length and mass of 16 captive epaulette sharks across 1 year and tracked female reproduction daily. We also collected length and mass data from an additional 72 wild‐caught sharks and 155 sharks from five previous studies and two public aquaria to examine the relationship between length and mass for this species. Even though data were derived from a variety of sources, a predictable length–mass relationship (R² = 0.990) was achievable, indicating that combining data from a variety of sources could help overcome knowledge gaps regarding basic life history characteristics. We also found that condition factor decreased during early life stages, then increased again into adulthood, with predictable changes across the female reproductive cycle. Finally, we determined that both Fulton's and girth condition analyses were comparable. Outcomes from this study uniquely provide body condition changes across the complete life history, including fine‐scale female reproductive stages, and validate the use of girths as a nonlethal whole‐organism energetic assessment for fishes.
... Such information can be used to determine sustainable harvesting rates, understand a population's potential for timely recovery, and/or develop protected areas or strategies for bycatch avoidance (Awruch, 2013). Although lethal sampling of a relatively large number of specimens has historically been the approach for studying the reproductive biology of elasmobranchs (Heupel and Simpfendorfer, 2010), sacrificing threatened species is in direct opposition to the conservation and management goals science is intending to support (Hammerschlag and Sulikowski, 2011). Given this nuance, non-lethal alternatives for collecting reproductive data should be validated and prioritized whenever possible (Hammerschlag and Sulikowski, 2011). ...
... Although lethal sampling of a relatively large number of specimens has historically been the approach for studying the reproductive biology of elasmobranchs (Heupel and Simpfendorfer, 2010), sacrificing threatened species is in direct opposition to the conservation and management goals science is intending to support (Hammerschlag and Sulikowski, 2011). Given this nuance, non-lethal alternatives for collecting reproductive data should be validated and prioritized whenever possible (Hammerschlag and Sulikowski, 2011). One promising technique that can be used to study the reproduction (reproductive cycles, maturity, reproductive habitats) of elasmobranchs is the quantification of sex steroids (reproductive hormones) in muscle tissues (Prohaska et al., 2013;Verkamp et al., 2021). ...
While lethal sampling can be the most effective technique to collect critical reproductive data for elasmobranchs, non-lethal techniques need to be validated for future use. Concentrations of reproductive hormones in plasma and muscle have been found to correlate to sexual maturity and/or reproductive cycles in oviparous as well as yolk-sac, placental, and histotrophic viviparous elasmobranchs, offering a potentially non-lethal technique to study reproduction. However, reproductive hormone analysis is scant for oophagous sharks. This study utilized muscle tissues from porbeagles Lamna nasus that were dissected for other life history studies and were stored frozen for up to 37 years to quantify testosterone (T) and estradiol (E2) concentrations in relation to previously-known maturity and reproductive stage. A total of 207 samples (92 males, 115 females) from porbeagles ranging in size from 80 to 256.5 cm fork length were analyzed. Muscle T and E2 concentrations were related to maturity and reproductive stage in porbeagles, with the highest T concentrations found in mature males during the spermatogenic season (summer) and the highest E2 concentrations found in gravid females. These results suggest muscle hormone concentrations have the potential to serve as a non-lethal proxy of reproductive stage in oophagous sharks. This study also demonstrates the value of specimen sharing and the potential for continued use of stored vertebral muscle tissue for reproductive hormone analysis in order to optimize the amount of data gained from biological samples. Future use of these methods would be particularly valuable for threatened species for which lethal sampling is restricted.
... So far, in this field of research large numbers of fish need to be sampled, whether through notified animal testing or euthanisation without a prior animal experiment, even though the final aim is to conserve the species. In order to reduce the number of fish killed, Hammerschlag and Sulikowski (2011) described how non-invasive methods can be used to study fish for some experimental questions. For example, for trophodynamic studies, the intestine is often dissected, and the contents analysed. ...
... Alternatives to this lethal method would be gastric lavage or faecal examination followed by DNA analysis. Gastric lavage under anaesthesia has been widely applied and, with a high survival rate successfully used for herbivorous fish as well as apex predatory fish (Barnett et al. 2010;Hammerschlag and Sulikowski 2011;Elston et al. 2015;Braga et al. 2017). These methods could ensure greater knowledge about the ecology and conservation of fishes, especially for populations of small and rare species that are endangered. ...
In mammalian research, the implementation of the 3Rs is ubiquitous. However, the adaptation of procedures for experimental work on fish seems less extensive in comparison, even though fish model organisms are common in a broad range of research fields already. To strengthen animal welfare in experimental research, we provide an overview of current research results, including studies on the nociception of fishes. Furthermore, we describe the potential of implementing the 3Rs in fish experimental research. In the context of "Reduction", we show alternative research methods to lethal sampling. Considering "Refinement", we point out possibilities to improve fish handling and indicate that adaptations to the individual species ecology are necessary. Under the aspect of "Replacement", we describe the high potential of cell cultures that can be obtained from fish tissue and give an overview of the already extensive use in ecotoxicology and virology. In addition, we illustrate that cell cultures could also be increasingly used for basic research.
Graphical abstract
... Traditionally, examination of the internal anatomy of fish requires the need to euthanise individuals (Ebert, 2005;Harry et al., 2010;Ruocco et al., 2006;Whitney & Crow, 2007). Although this approach is still widely used (Anderson et al., 2018;Heupel & Simpfendorfer, 2010;Sado et al., 2019), it is not suitable for the study of species of conservation concern (Hammerschlag & Sulikowski, 2011). To overcome this issue, non-lethal methods such as ultrasonography and endoscopy are being developed and validated (Sulikowski et al., 2007). ...
... In the present study, waterproof and contactless ultrasonography was Traditionally used techniques to obtain data on elasmobranch reproduction include lethal sampling and animal restraint (Anderson et al., 2018;Hammerschlag & Sulikowski, 2011). In view of the recent declines in many elasmobranch populations due to fisheries and habitat loss (Pacoureau et al., 2021), such practices are now perceived as detrimental and are often prohibited by local conservation laws. ...
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.
... One candidate method is the measurement of reproductive hormone levels in the blood (Awruch et al., 2008a;Awruch et al., 2014;Fujinami and Semba, 2020) and muscle (Prohaska et al., 2013), which have been adopted as non-lethal assessment of reproductive stages in wild populations. Another nonlethal technique is ultrasonographic monitoring of reproductive organs with simultaneous hormone measurement (Anderson et al., 2018;Hammerschlag and Sulikowski, 2011;Mylniczenko et al., 2019;Nau et al., 2018;Nozu et al., 2018;Sheldon et al., 2018;Sulikowski et al., 2016;Wittamore et al., 2010). In our previous study using captive sexually mature zebra sharks Stegostoma tigrinum, ultrasonographic images of ovaries and oviducts were collected to monitor changes in maximum follicle diameter and the number of egg capsules in the oviducts, which were correlated to monthly changes in plasma E2, T, and P4 measured concurrently . ...
... According to Dulvy et al. (2021), approximately 34% of shark and ray species are threatened with extinction. Therefore, non-lethal assessments of reproductive condition and its endocrine control are highly desirable among elasmobranch researchers (Awruch et al., 2008a;Awruch et al., 2014;Becerril-Garcia et al., 2020;Hammerschlag and Sulikowski, 2011;Prohaska et al., 2013;Wittamore et al., 2010). ...
The many diverse reproductive strategies of elasmobranchs (sharks, skates and rays) from lecithotrophic oviparity to matrotrophic viviparity have attracted significant research attention. However, the endocrine control of elasmobranch reproduction is less well-documented largely due to their reproductive characteristics, such as a long reproductive cycle, and/or repeated internal fertilization using stored sperm in oviparous species. In the present study, for the first time, we succeeded in non-invasive monitoring of the continuing egg-laying cycle of the cloudy catshark Scyliorhinus torazame using portable ultrasound devices. Furthermore, long-term simultaneous monitoring of the egg-laying cycle and measurement of plasma sex steroids revealed cycling patterns of estradiol-17β (E2), testosterone (T) and progesterone (P4). In particular, a decline in T followed by a reciprocal surge in plasma P4 were consistently observed prior to the appearance of the capsulated eggs, implying that P4 is likely associated with the ovulation and/or egg-case formation. While the cycling pattern of E2 was not as apparent as those of T and P4, threshold levels of E2 (> 5 ng/mL) and T (> 1 ng/mL) appeared to be crucial in the continuation of egg-laying cycle. The possibility to trace the dynamics of plasma sex steroids in a single individual throughout the reproductive cycles makes the catshark a useful model for regulatory and mechanistic studies of elasmobranch reproduction.
... However, such studies have established a strong link between concentrations of key hormones and morphological reproductive changes (Gelsleichter and Evans 2012;Awruch 2013;Prohaska et al. 2013b). As a result, reproductive hormone analysis represents an opportunity to study parameters such as the maturity or reproductive status of individuals or the reproductive cycle of populations in a broader range of species without the need to euthanase individuals (Hammerschlag and Sulikowski 2011). Such non-lethal 'standalone' studies have been applied only to a few shark species (Awruch et al. 2014;Sulikowski et al. 2016;Irigoyen et al. 2018), but this approach is becoming increasingly imperative, given that many species are threatened or vulnerable to overexploitation (Hammerschlag and Sulikowski 2011;Dulvy et al. 2014). ...
... As a result, reproductive hormone analysis represents an opportunity to study parameters such as the maturity or reproductive status of individuals or the reproductive cycle of populations in a broader range of species without the need to euthanase individuals (Hammerschlag and Sulikowski 2011). Such non-lethal 'standalone' studies have been applied only to a few shark species (Awruch et al. 2014;Sulikowski et al. 2016;Irigoyen et al. 2018), but this approach is becoming increasingly imperative, given that many species are threatened or vulnerable to overexploitation (Hammerschlag and Sulikowski 2011;Dulvy et al. 2014). ...
Accurate reproductive information is crucial for the effective management of sharks. Here, we used non-lethal methods to evaluate reproductive hormone profiles of blacktip sharks (Carcharhinus limbatus) off the coast of southern Florida (FL) as part of a preliminary investigation of this species' reproductive patterns in the region. Circulating testosterone concentrations in males ranged from 0.04 to 320.7 ng mL −1 , and concentrations peaked during months previously shown to represent peak spermatogenic activity. In females, circulating concentrations of oestradiol (E2) ranged from 12.5 to 941.4 pg mL −1 , and progesterone (P4) ranged from 30.1 to 821.2 pg mL −1. E2 peaked during months with peak vitellogenic and ovulatory activity in previous studies; P4 displayed less variability among months. In general, changes in monthly hormone concentrations align well with the timing of reproductive events in C. limbatus in other regions. However, because of low monthly sample sizes and a lack of reproductive status confirmation, the female profiles raise interesting questions about this population's reproductive cycle that could be explored in future studies. Additional studies should collect larger monthly samples and incorporate supplementary data to provide more insight into the reproductive cycle of this species in southern FL.
... Species identification issues as well as potential under-or over-reporting of white shark may not be as prevalent in the data sources analyzed by Curtis et al. (2014), so this trend is expected to be more robust. Relative to life history data, targeted lethal sampling to evaluate biological characteristics is neither feasible nor desirable for populations that are currently at low abundance and have such low intrinsic rates of increase (Hammerschlag & Sulikowski, 2011;Heupel & Simpfendorfer, 2010). ...
... These results flag research on reproductive dynamics (e.g., maturation, senescence, reproductive periodicity, and the potential for resting between reproduction events) as critical given the possibility of increased longevity (Huveneers et al., 2018). Exploring such questions for white shark will require further development and validation of nonlethal sampling methodologies, such as hormonal analysis coupled with ultrasound imaging (Hammerschlag & Sulikowski, 2011). ...
To effectively protect at‐risk sharks, resource managers and conservation practitioners must have a good understanding of how fisheries removals contribute to changes in abundance and how regulatory restrictions may impact a population trajectory. This means they need to know the number of animals being removed from a population and whether a given number of removals will lead to population increases or declines. For white shark (Carcharodon carcharias), theoretical quantities like the intrinsic rate of population increase or rebound potential (ability to increase in size following decline) are difficult to conceptualize in terms of real‐world abundance changes, which limits our ability to answer practical management questions. To address this shortfall, we designed a simulation model to evaluate how our understanding of longevity and life history variability of white shark affects our understanding of population trends in the Northwest Atlantic. Then, we quantified the magnitude of removals that could have caused historical population declines, compared these to biologically based reference points, and explored the removal scenarios which would result in population increase. Our results suggest that removals on the order of 100s of juveniles per year could have resulted in population‐level declines in excess of 60% during the 1970s and 1980s. Conservation actions implemented since the 1990s would have needed to be nearly 100% effective at preventing fishing mortality in order for the population to double in abundance over the last 30 years. Total removals from all fleets needed to be exceptionally small to keep them below biological reference points for white shark in the Northwest Atlantic. The population's inherent vulnerability to fishing pressure reaffirms the need for restrictive national and international conservation measures, even under a situation of abundance increase.
... Non-lethal approaches to Sulikowski JA, Perisic studying reproduction in sharks (and other elasmobranchs) have negated the need to sacrifice the animals (e.g. Hammerschlag and Sulikowski, 2011;Sulikowski and Hammerschlag, 2023), which has created opportunities to better manage threatened species. One such approach has been the development of a portable, high-definition underwater ultrasound that has been used to determine if sharks are gravid in situ (e.g. ...
The reproductive state of wild, free-swimming tiger sharks (Galeocerdo cuvier), was assessed using underwater ultrasonography at a diving site in Fuvahmulah, a Maldivian atoll within the central Indian Ocean. The presence of embryos were observed in 93% of the adult sharks (26/28) and two distinct embryonic size groups were observed within the subset of scanned adult females. The results suggest that the observed dive site functions as a gestation ground and builds upon previous work that emphasizes the importance of dive sites for the collection of biological data for shark conservation and management.
... In order to understand the life-history, ecology and physiology of pelagic sharks, and identify their roles in the different systems they occupy, scientists have employed a variety of developing methods. Historically, studies relied on direct observation using tools such as mark-recapture, with often low recapture success rates (at their highest generally around 20%; Kohler et al., 2002, Queiroz et al., 2005, Costa et al., 2012, Madigan et al., 2015; or controversial lethal sampling of individuals to obtain information on diet (stomach content analysis), reproductive status (examination of internal reproductive organs), or age and growth rates (enumeration of vertebral growth zones) (Cortés, 1997, Hammerschlag and Sulikowski, 2011. More recently, the advancement of electronic tag technologytelemetryhas allowed for more precise and long-term tracking of marine vertebrate movements (Hussey et al., 2015). ...
As the world faces the threats of multiple compounded and worsening crises, scientists are racing to gather the knowledge necessary to safeguard entire ecosystems and species. Technological advances are continuously facilitating more in-depth studies to understand the mechanisms driving species functioning and variations among and within populations, communities, and individuals. New methods are providing insights into difficult to access environments and species such as the open ocean. The following thesis uses theoretical and empirical approaches to understand the drivers of variation in ecological niches of large marine predators. One of the methods commonly used to study a species resource use is stable isotope analysis (SIA). However, the relationship between variation in stable isotope values in the tissues of consumers and their diet is often misconstrued or over-simplified. Here, we lay out the underlying factors that influence stable isotope ratios and how these can be accounted for when designing an ecological study. I then review new advances in stable isotope technologies and how compound-specific SIA can be used to ask questions about the life-history of a broad range of species. Having shown the value in combining biochemical methods with other disciplines, I apply this approach to study the ecology of large marine vertebrates in Ireland. By using fatty acid analysis in combination with reproductive hormone analysis, biologging, morphometrics and observations, I investigate the ecology and physiology of blue sharks, Prionace glauca, in Ireland. This population of predominantly female individuals in varying stages of maturity show indications of a seasonal change in resource use between the June and November ? possibly indicating opportunistic foraging on abundant gelatinous or planktonic prey. Finally, I present the results from our tagging efforts on mature female porbeagle sharks, Lamna nasus, caught in Donegal (Ireland) in April 2022. As I have followed these two individuals over the past nine months, both have crossed many environmental and jurisdictional boundaries but have displayed high inter-individual variation. I argue the need for increased and continued cross-country collaboration in the Northeast Atlantic to study and manage this critically endangered species. The work carried out here emphasises the value in moving our field from uni- and multidisciplinary approaches towards more holistic interdisciplinary approaches, particularly when our aim is the sustainable preservation of large oceanic migrators.
... As a result, approximately one-third of all living elasmobranch species are listed as "Vulnerable" to "Critically Endangered" and 14% considered as "Data Deficient" by the International Union for the Conservation of Nature (IUCN) 2022 Red List (IUCN, 2022). Understanding components of a species' reproductive biology (i.e., age-at-maturity, gestation period, reproductive mode, reproductive cyclicity) and life-history strategies related to reproduction are essential for effective management of wild populations (Hammerschlag and Sulikowski, 2011;Natanson et al., 2019). For example, such information can assist stock assessments thereby informing management decisions related to protected area designation (Awruch, 2013). ...
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.
... Considering the large-scale movements undertaken by these migratory sharks, and therefore, the wide range of habitats used by them, there is a need for a more complete diet description using an integrative approach. In addition, the conservation status of this animal requires nonlethal techniques (Hammerschlag and Sulikowski, 2011). Stable isotope analysis (SIA) presents an effective research method as it integrates diet information from larger temporal scales (Vander Zanden et al., 2015) while avoiding the need for animal sacrifice (Sanderson et al., 2009;Shiffman et al., 2012). ...
The broadnose sevengill shark (Notorynchus cepedianus) is classified as Vulnerable by the IUCN, and its population in the Southwest Atlantic is declining. Despite some progress in understanding the ecological requirements of the sevengill shark, there are still several information gaps. Essential aspects of its trophic ecology, such as main prey items or key feeding grounds, remain uncertain and this information is essential for developing effective conservation strategies. Stable isotopes and spontaneous regurgitations were analyzed to describe the trophic ecology of sevengill sharks within a marine protected area (MPA) of Península Valdés in Patagonia, Ar-gentina. Analysis of spontaneous regurgitations revealed that the southern elephant seal (Mirounga leonina) was the primary prey item (70%) for the sevengill shark, during abundance peaks of both species in the MPA. However , the stable isotope analysis indicated that the teleosts were the main prey item, and the overall contribution of the elephant seal to the diet of the sevengill shark was around 30%. In addition, the contribution of each prey group varied with the size of the individuals. The estimated trophic position was 4.43, placing the species among the apex predators of the region. This study confirmed the use of the MPA as an essential foraging ground and contributed to identifying its main prey items. Also, it reflects the need to expand conservation tools beyond this particular coastal protection.
... Ascertaining accurate information on life history traits, such as age and growth, can help to classify species' potential susceptibility to anthropogenic threats (Emmons et al., 2021). Furthermore, accurate age and growth estimates are important when assessing the vulnerability of a population and determining the risk of overexploitation (Hammerschlag and Sulikowski, 2011) because these estimates are often used directly in a variety of assessment models (Hoenig and Gruber, 1990;Baje et al., 2018;Flinn and Midway, 2021). ...
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.
... The third potential reason for the lack of new mechanistic endocrinological work could be a shift in focus to non-lethal techniques within the research community. Given the imperiled state of many chondrichthyan species globally (Dulvy et al., 2021;Sherman et al., 2023), 21st century research has largely shifted toward non-lethal methodologies (Hammerschlag and Sulikowski, 2011). For example, sex steroids are useful for indicating maturity, non-lethally. ...
... As an important component of the ecosystem, sharks influence the structure and the functionality of marine communities (Camhi et al., 2008). Major populations of oceanic predators, such as large sharks, are impacted by anthropogenic threats due to their low fecundity, low growth rates, late sexual maturation, and reproductive aggregations (Baum et al., 2003;Hammerschlag and Sulikowski, 2011;Worm et al., 2013;Barreto et al., 2017). Furthermore, there are limitations and challenges in data availability to investigate population decays, extinction threats, and potential consequences for marine ecosystems (Worm et al., 2013; Ward-Paige and Corrêa et al. ...
... Uncertainty in fecundity is common, and fecundity may be underestimated due to the loss of embryos during capture, leading to an underestimation of litter size . As such, the improvement of stock assessments in future research requires the collection of more reliable litter size data through onboard observation, also through non-invasive techniques like ultrasound (Hammerschlag and Sulikowski, 2011). ...
While data on fisheries, in general, may be limited, demographic models provide a valuable tool for gaining insights into population dynamics when a more comprehensive understanding is not feasible. Demographic models may be used in the study of population dynamics because they only require life history parameters. We performed a quantitative population projection on the basis of expert knowledge, estimated mortality, and published information on the life history of two hammerhead shark species, smooth hammerhead (Sphyrna zygaena) and scalloped hammerhead (Sphyrna lewini), and we conducted an elasticity analysis determine the sensitivity of each life stage to the population growth rate. This study highlights the overexploitation challenges faced by these two ecologically important and vulnerable species and emphasizes the need to reduce fishing mortality is crucial to achieving population growth. To increase the accuracy of demographic estimates for these species, it is necessary to conduct further investigations into their natural mortality and reproductive traits. The approach used in this study can be applied to other shark species across a diverse range of taxa with limited data on catch and effort. Moreover, this method is easy to use and interpret and can be used to predict future population size for data-limited species.
... One particular life history stage that is critical for establishing site-based conservation strategies, such as marine protected areas or time/area closures is an understanding of where gravid sharks spend their time gestating/and or give birth (Chapman et al., 2013;Sulikowski et al., 2016). However, historically, such reproductive data was collected from sacrificed animals from fisheries, which is problematic for species that have been classified as threatened and in the case of shark diving tourism, can also have a negative socioeconomic impact (Hammerschlag and Sulikowski, 2011). Thus, new approaches to studying elasmobranchs increasingly include non-lethal sampling methods (Penfold and Wyffels, 2019). ...
A prototype, fully submersible, high definition ultrasound was used to determine the reproductive state of wild, free-swimming bull sharks, Carcharhinus leucas, at a provisioned shark diving site in Playa del Carmen, Mexico. During two opportunistic dives, the presence of embryos was confirmed in three female sharks (greater than 2.0 m total length) and emphasizes the importance of developing and linking emerging technologies with shark diving sites for the conservation of elasmobranch species.
... In female elasmobranchs, the developmental stage of the reproductive tract is often determined via postmortem assessment (Sulikowski et al. 2005, Licandeo et al. 2007, Kyne et al. 2008, Quiroz et al. 2009). However, there is an obvious need to use and promote non-lethal methods to describe the reproductive organs (Hammerschlag & Sulikowski 2011), especially for Critically Endangered species such as the flapper skate, where individual survival is a priority. Advances in ultrasound technology have made the non-lethal assessment of the reproductive tract of female elasmobranchs in field-based situations more feasible and have been successfully used on livebearing elasmobranch species (Carrier et al. 2003, Jirik & Lowe 2012, Daochai et al. 2016, Sulikowski et al. 2016, Anderson et al. 2018, Penfold & Wyffels 2019, Tomita et al. 2019. ...
Due to global population declines, there is a pressing need for data on the life history traits of many elasmobranch species to support the development of species-specific management plans. A lack of information on the reproductive cycle of the Critically Endangered flapper skate Dipturus intermedius was recently identified as a hindrance to its conservation. To address this data gap, we combined non-lethal ultrasound and hormone analysis to investigate the size at maturity and reproductive cycle of the flapper skate in the Loch Sunart to the Sound of Jura Marine Protected Area off the west coast of Scotland. In-field ultrasound imagery revealed encapsulated eggs in utero and was used to determine the presence and size of ovarian follicles. Combining these images with levels of plasma testosterone, progesterone and oestradiol provided valuable insights into the timing of the reproductive cycle and maturity state of the flapper skate. This preliminary study suggests that male skate start to mature at 165 cm and females at 203 cm total length. Oestradiol appears to be the primary hormone controlling the female reproductive cycle and, along with ultrasound images, indicates that females lay pairs of eggs throughout a winter egg-laying season. Our study further highlights how non-lethal methods can be used to investigate the life history of oviparous elasmobranchs in the field. This information will support the identification of important life history groups and their associated habitats and contribute to the development of management strategies for these species.
... Due to the fact that the CA enzyme is present in different taxonomic groups, it is believed that its behavior in elasmobranchs, whether marine, euryhaline or freshwater species, is similar to bony fishes. However, information on the role of CA in this group is still scarce, due to the challenges for experimental studies on sharks and rays, notably the logistical difficulty of capture and maintenance under human care, and the need for non-lethal studies given the high risk of extinction of this group (Hammerschlag and Sulikowski, 2011). In this context, the present study aims to bring an overview of CA studies in elasmobranchs, establishing future perspectives for this knowledge area. ...
The enzyme carbonic anhydrase (CA) has well-known functions in acid-base balance, respiratory gas exchange, and osmoregulation in teleost fishes. However, studies concerning the role of CA in elasmobranchs are still scarce. Therefore, the aim of this study is to present the current status of CA studies in sharks and rays, as well as to identify gaps and emerging needs, in order to guide future studies. This review is organized according to the main roles of CA, with further considerations on climate change and CA effects indicated as paramount, as strategies in the face of climate change can be crucial for species response. The literature review revealed a reduction in publications on CA over the years. In addition, a historical research differentiation is noted, where the first assessments on the subject addressed investigations on basic CA functions, while the most recent studies present a comparative approach among species as well as interdisciplinary discussions, such as ecology and phylogeny. Considering that most elasmobranchs are threatened, future studies should prioritize non-lethal methodologies, in addition to expanding studies to climate change effects on CA.
... Moreover, understanding these reproductive characteristics is necessary for establishing effective site-based management strategies, such as marine protected areas or time/area closures to safeguard key life-history stages (3). However, reproductive data on fishes are traditionally derived from sacrificing specimens and inspecting reproductive organs (4,5). In addition, the scale and often remote movements of marine predators make identifying their critical reproductive sites especially challenging (6). ...
Determining where and when animals give birth is critical for establishing effective conservation management that protects vulnerable life stages (e.g., pregnant females and newborns) and places (e.g., nursery grounds). To date, this information has been elusive in the case of highly migratory sharks in the wild. Here, we report on the deployment a of novel intrauterine satellite tag implanted in two highly mobile apex predators, the tiger shark (Galeocerdo cuvier) and the scalloped hammerhead (Sphyrna lewini), that remotely documented the location and timing of birth by a highly migratory oceanic animal in the wild. This novel technology will be especially valuable for the protection of threatened and endangered shark species, where protection of pupping and nursery grounds is a conservation priority.
... and Scyliorhinus spp.) due to logistical limitations (Bernal and Lowe, 2015). Furthermore, lethal studies are categorically discouraged for both top predators (Hammerschlag and Sulikowski, 2011) (e.g., great white sharks, tiger sharks, and bull sharks) and threatened species (e.g., hammerhead sharks-Sphyrna spp., limiting the applications of controlled toxicological studies to inform elasmobranch conservation. ...
... For example, muscle and cartilage from fin tissue of elasmobranchs has a relatively long estimated isotopic turnover rate and can be used to examine long-term integrated movement patterns, whereas plasma has a relatively shorter isotopic turnover rate, which can be used to investigate seasonal movement patterns (MacNeil et al. 2006;Logan and Lutcavage 2010;Matich et al. 2011;Hussey et al. 2012;Kim et al. 2012). Further, given that only a small tissue sample is needed, it is a minor-invasive and powerful tool to study the movements of cryptic and vulnerable species (Hammerschlag and Sulikowski 2011;Hussey et al. 2012). ...
Context Understanding migratory species’ habitat selection is complicated by variation in movement strategies. Stable-isotope analysis provides a powerful tool to investigate such variation. Aims We used acoustic telemetry and stable-isotope analysis to better understand the movement strategies of Port Jackson sharks. Methods We compared the δ13C and δ15N values of fin tissue from acoustically tracked individuals that undertook three distinct movement strategies. Hierarchical cluster analysis was then used to cluster movement strategies of a larger sample of sharks on the basis of δ13C and δ15N values. Key results Tracked individuals that remained in Jervis Bay were enriched in 13C, compared with those that migrated south after the breeding season. Individuals were assigned to six clusters and δ13C and δ15N values indicated that migrating males and females may utilise different geographical areas or niches during the non-breeding season. Conclusions By using stable isotope analysis and acoustic telemetry, we identified distinct groups of Port Jackson sharks with similar broad-scale movement strategies. Implications These variable movement strategies may lead to different reproductive fitness advantages on an individual and population level, having implications for the broader ecosystem, given the important role mesopredators play in southern reef marine ecosystems.
... This paucity of data is a result of the complexity of capturing and sampling the shark while maintaining minimal injury to the animal. Indeed, researchers are constantly finding new, alternative sampling methods that are less harmful and non-invasive (Hammerschlag and Sulikowski, 2011). These studies have characterized the microbiome of different shark species (such as Alopias vulpinus, Sphyrna tiburo and Triakis semifasciata) from various geographic locations and are the first examples in this field (Doane et al., 2017(Doane et al., , 2022Leigh et al., 2021;Perry et al., 2021). ...
Sharks, as apex predators, play an essential ecological role in shaping the marine food web and maintaining healthy and balanced marine ecosystems. Sharks are sensitive to environmental changes and anthropogenic pressure and demonstrate a clear and rapid response. This designates them a “keystone” or “sentinel” group that may describe the structure and function of the ecosystem. As a meta-organism, sharks offer selective niches (organs) for microorganisms that can provide benefits for their hosts. However, changes in the microbiota (due to physiological or environmental changes) can turn the symbiosis into a dysbiosis and may affect the physiology, immunity and ecology of the host. Although the importance of sharks within the ecosystem is well known, relatively few studies have focused on the microbiome aspect, especially with long-term sampling. Our study was conducted at a site of coastal development in Israel where a mixed-species shark aggregation (November–May) is observed. The aggregation includes two shark species, the dusky (Carcharhinus obscurus) and sandbar (Carcharhinus plumbeus) which segregate by sex (females and males, respectively). In order to characterize the bacterial profile and examine the physiological and ecological aspects, microbiome samples were collected from different organs (gills, skin, and cloaca) from both shark species over 3 years (sampling seasons: 2019, 2020, and 2021). The bacterial composition was significantly different between the shark individuals and the surrounding seawater and between the shark species. Additionally, differences were apparent between all the organs and the seawater, and between the skin and gills. The most dominant groups for both shark species were Flavobacteriaceae, Moraxellaceae, and Rhodobacteraceae. However, specific microbial biomarkers were also identified for each shark. An unexpected difference in the microbiome profile and diversity between the 2019–2020 and 2021 sampling seasons, revealed an increase in the potential pathogen Streptococcus. The fluctuations in the relative abundance of Streptococcus between the months of the third sampling season were also reflected in the seawater. Our study provides initial information on shark microbiome in the Eastern Mediterranean Sea. In addition, we demonstrated that these methods were also able to describe environmental episodes and the microbiome is a robust measure for long-term ecological research.
... Interestingly, even with some data available on stomach eversion, this has not been suggested as a stress-related behavioral proxy to date. Usually, reports are focused on the basic biology of affected individuals or on feeding habit evaluations, using eversion as a non-lethal approach to access stomach content (Hammerschlag and Sulikowski 2011). In the case of commercial fisheries, stomach eversion is commonly noted in sharks (NW personal communication), although published data for captured animals are only available for sharks. ...
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.
... When it comes to killing animals in the name of conservation, even if methods can cause an instantaneous death without pain or suffering, the consequences of removing that individual as a member role of its social structure, its genetic contribution, or its trophic role in the ecosystem can lead to harms to other animals and ecosystems. Killing for conservation, especially for sampling purposes alone, needs greater scrutiny and humane, nonlethal alternatives must be developed to obtain conservation data (Hammerschlag and Sulikowski 2011). Despite conservation's ethical underpinnings in environmental ethics, the ethical costs to individual animals are not adequately considered in conservation, even in the presence of animal care ethics committees or peer review (Vucetich and Nelson 2007). ...
There isn’t one conversation about animal ethics. Instead, there are several important ones that are scattered across many disciplines.This volume both surveys the field of animal ethics and draws professional philosophers, graduate students, and undergraduates more deeply into the discussions that are happening outside of philosophy departments. To that end, the volume contains more nonphilosophers than philosophers, explicitly inviting scholars from other fields—such as animal science, ecology, economics, psychology, law, environmental science, and applied biology, among others—to bring their own disciplinary resources to bear on matters that affect animals.
It is a resource designed for anyone interested in the moral issues that emerge from human interactions with animals.
Chapter 31 - Explores is it ever ok to kill wild animals? How can we apply a common framework globally for assessing conservation interventions where root causes are ultimately human behaviour.
... An important step in this direction may comprise taking advantage of dead individuals caught in artisanal and commercial South Atlantic fisheries, following the increasing trend for non-lethal studies on this species noted in other regions (Hammerschlag & Sulikowski, 2011). However, it is important to note that carcass decomposition status should be considered when evaluating dead individuals, and sampling should be standardized to individuals in the same decomposition stage, as what is routinely carried out for other marine megafauna representatives, such as marine mammals, where a standardized carcass decomposition code is employed (Geraci & Lounsbury, 2005). ...
The tiger shark (Galeocerdo cuvier) has been relatively well assessed concerning biology and ecology aspects in both Atlantic and Pacific North America and in Caribbean waters. The amount of data in these regions has led to the species protection under capture quotas and with the creation of sanctuaries. The reality in developing countries, however, is the exact opposite, with scarce information on the species in the southern hemisphere, namely South American and African waters. In these regions, protection measures are insufficient, and studies on tiger shark biology and ecology are scarce, significantly hindering conservation and management efforts. Thus, the aim of this study was to compile scientific literature on the tiger shark in the South Atlantic and discuss the impact of these data (or lack thereof) distributed within a total of ten research categories for guiding management plans. In total, 41 scientific publications on different G. cuvier biology and ecology aspects were obtained. The most studied topics were Feeding Ecology (n = 12), followed by Human Interactions (n = 8), and Movements and Migration (n = 7). Northeastern Brazil (Southwest Atlantic) was the most researched area, probably due to the higher coastal abundance of tiger sharks in this area, alongside a high number of recorded attacks, justifying funding for studies in the region. No studies carried out in other South American or African countries were found. It is important to mention that even though some research topics are relatively well covered, a severe knowledge gap is noted for risk assessments and fisheries management, with a proposition for the implementation of sanctuaries noted. This is, however, particularly worrisome, as the South Atlantic is mostly unexplored in this regard for tiger sharks. It is also important to note how different the attention given to this species is in the North Atlantic when compared to the South region. Lastly, we highlight that the existence of sub-populations, the lack of migratory corridors geographically connecting distinct areas used by the species, and the lack of fisheries statistics on tiger shark landings, all increase the vulnerability of this species in the South Atlantic.
... A number of marine vertebrates are known to connect widely separated ecosystems via large-scale movements such as seasonal migrations. Elasmobranchs, in particular, are often considered as important for ecosystem connectivity, yet large-scale movement studies have been focused on apex predatory sharks (Hammerschlag and Sulikowski 2011) with little effort to understand the role of mesopredatory rays in linking habitats. The vast majority of studies investigating ray movements have had receiver arrays limited to a single coastal bay, beach, or estuary. ...
The blue stingray Dasyatis chrysonota is an important and endemic coastal inhabitant of southern African coastal waters however, it is listed as Near Threatened with declining populations. Understanding it’s spatial ecology in the context of current Marine Protected Areas (MPAs) is vital to not only inform population dynamics and ecological roles, but to determine whether currently zoned MPAs can provide sufficient protection to this species. Twenty-seven individuals were monitored using the Acoustic Tracking Array Platform (ATAP—a nation-wide collaborative network of acoustic receivers) for up to 4.5 years. Individuals displayed site affinity to defined regions of the coast, with the majority of detections for most individuals being recorded in the shallow bay/coastal shelf they were tagged in. However, important movement corridors linking different habitats were also identified (inshore vs offshore and coastal bay vs coastal shelf habitats). This habitat use varied monthly and was influenced by temperature, with individuals displaying restricted movements to the shallow bay habitat in summer when deeper waters were much colder. The large collaborative nature of the ATAP allowed for the monitoring of a benthic ray across large spatial scales for the first time, challenging preconceived notions that small undulatory batoids cannot travel large distances (many individuals were found to travel up to 200 km). Insights can also assist in local management of this species, and highlight that current MPA zonation may not be sufficient to protect blue stingrays from further population declines.
... Ideally, targeted non-lethal research will address each of these deficiencies for at-risk sharks (e.g., Hammerschlag and Sulikowski, 2011) such that the underlying dynamics of individual populations can be appropriately characterized. This would enable future quantitative predictions of status and response to threats for individual populations within a Population Viability Analysis (PVA; e.g., Morris and Doak, 2002;Dulvy et al., 2004). ...
It can be difficult to determine whether a prohibition to exploitation ensures effective conservation or recovery for species that remain exposed to fishing effort and other sources of mortality throughout their range. Here we used simulation modeling of four life history scenarios (different productivity and population size) to contextualize potential population response to multiple levels of mortality, using white sharks (Carcharodon carcharias) in South Africa as a case study. The species has been protected since 1991, yet substantial uncertainty about population dynamics persists and recent declines at two aggregation sites have renewed conservation concern. All scenarios indicated that annual removals in the 10s of individuals would substantially limit the potential for and magnitude of any abundance increase following prohibition. Because average known removals from the KwaZulu-Natal Sharks Board's Bather Protection Program have typically remained higher than these thresholds, they likely eliminated much of the conservation benefit derived from prohibition. The only life history scenario to achieve appreciable increase when simulated removals were similar to published averages assumed maturation occurred at a much younger age than currently understood. Our results demonstrate why general application of life history-based simulations can provide a useful mechanism to evaluate the biological plausibility of life history information and abundance trends, and to explore the scope for population response to recovery actions. For South Africa, our results suggest that even known levels of white shark removals, which likely underestimate total removals within their range, may be sufficient to drive abundance decline and new mitigation measures may be required to ensure population recovery.
... A difference in the metals found between areas in this study may mean that for some circumstances muscle biopsy is a valid method, particularly as it is non-lethal. There has been some debate over the need for lethal sampling in elasmobranch science, especially when impacts on threatened species are concerned (Heupel & Simpfendorfer, 2010;Hammerschlag & Sulikowski, 2011) and a method of determining metal contamination without euthanising members of a threatened species would be ideal. ...
Information about the movement, seasonality, and use of habitats by marine animals is vital for the mitigation of potential anthropogenic impacts. Ray species may be particularly at risk as they regularly inhabit coastal and estuarine waters. In New Zealand to-date, there has been scant research on the ecology of native ray species in estuarine habitats. In particular, there is a dearth of knowledge pertaining to the spatio-temporal use of the range of habitats within estuaries. The research detailed in this thesis was aimed at addressing the shortfall of information. First, a review of the methodology utilised in ascertaining movement behaviour in non-shark-like batoid elasmobranch species was carried out, as optimisation of tagging research technique underpins the ability to track behaviour of these organisms for long periods. Most studies reviewed adopted tag anchor techniques used on teleost fishes or sharks. As a consequence, the quality of information pertaining to ray habitat use and movements was, in many circumstances, poor. Synthesis of tag longevity using differing anchor methods and field and aquarium longevity experiments led to a recommendation of nylon umbrella darts for soft-skinned non-shark-like rays such as Bathytoshia brevicaudata. Second, seasonality in habitat use within the Tauranga Harbour system was examined using monthly counts of the feeding excavations of Myliobatis tenuicaudatus. This study expanded previous estimations of seasonality and feeding habitat choice in estuaries. It determined that temperature-mediated sinusoidal seasonal patterns in feeding behaviour over a period of 24 months, differed in magnitude and peak month across a range of spatial scales. This could suggest some form of sequential habitat use. Unlike previous studies, evidence of ray feeding was found year-round. This behavioural pattern has implications for calculations of sediment turnover and transport. Peak turnover estimates of ray origin from this study doubled previous estimated calculations. In addition, infaunal prey density, and locational aspects of estuary ‘sub-habitats’ characterised as various ‘zones’ as compared to ‘harbour basin’ habitats, were all found to be influential in the prediction of M. tenuicaudatus feeding activity. There were inverse seasonal differences in the relationship between densities of large infaunal bivalves (putative prey items) and ray feeding activity, suggesting that during some periods, other prey types (soft bodied organisms) may also be important. Suggestions are made that perceived predator risk and human disturbance may have a role in driving habitat preferences in addition to prey density. This study also found that natural mangrove fringe is preferred by M. tenuicaudatus for feeding habitat over areas of ‘fringe’ that had been trimmed to prevent mangrove spread. The implications of this are significant as there is a reduction in ideal feeding habitat with ongoing mangrove trimming regimes. Finally, quantification of metal body burden of M. tenuicaudatus identified low levels of some heavy metals in rays from Tauranga Harbour when compared to Porirua Harbour, and that metals in rays from the outer coast of the Bay of Plenty region were likely to be of volcanic origin. Significantly different metal assemblages of estuarine and offshore animals combined with feeding evidence found year-round in Tauranga Harbour, suggests a separation in populations between these areas. Overall however, it is clear that metal content in Tauranga Harbour rays lies below FZANZ levels of concern and the harbour may be classified as relatively unpolluted. However, the behavioural patterns of rays clearly lead them away from shallower sub estuary areas, that are known to be more contaminated by anthropogenic activity.
In conclusion, this thesis provides previously unknown information about the habits and ecology of the important estuarine mesopredator M. tenuicaudatus in the context of anthropogenic risk associated with an urbanised harbour ecosystem. The information will allow informed management of harbour activities and developmental options with regard to conservation of an ecologically important species.
... However, perhaps because of sampling difficulties and costly logistics, studies focusing on marine taxa are yet scarce in comparison with terrestrial taxa (Dambach and Rödder 2011), and from those published so far applying ecological niche models (ENMs) for marine taxa, over half focus on groups like bony fish, molluscs, and marine mammals (Melo-Merino et al. 2020), while elasmobranchs are, to some degree, neglected. For threatened species, the use of such noninvasive methodologies is of paramount importance to provide the basis from which conservation efforts can be planned and implemented (Hammerschlag and Sulikowski 2011). ...
Climatic changes are disrupting distribution patterns of populations through shifts in species abiotic niches and habitat loss. The abiotic niche of marine benthic taxa such as skates, however, may be more climatically stable compared with the upper layers of the water column, which are more exposed to immediate impacts of warming. Here, we estimate climate change impacts in Riorajini, a tribe of four skates, as a proxy to evaluate the vulnerability of a temperate coastal zone in the Southwest Atlantic, and study niche dynamics in a scenario of environmental changes on this group of threatened species. We modelled the abiotic niche of each species under present climatic conditions (2000–2014), projected them to the future (2100), then measured distributional stability, expansion, and unfilling. Our results revealed abiotic stability between the scenarios modelled despite the advancement of climate change, suggesting that the benthic layers where these skates occur may be a refuge from the increasing thermal stress. However, the exposure of shallow waters to climate change may be detrimental to nursery habitats. Thus, although their abiotic niche may remain stable in the future, the loss of extension of occurrence might be a peril for them with climate change.
... Other measures, such as assessments of lethal limits, freezing points and supercooling capability are frequently lethal for the individuals used in the assessment (Sinclair et al., 2015). Therefore, sample sizes may be necessarily low when species are of significant conservation importance or where it is difficult to ethically justify experimentation on a larger number of individuals (Hammerschlag & Sulikowski, 2011;Taborsky, 2010). Thermal limits can, however, exhibit substantial within-population variation (Feder et al., 1987;Spicer & Gaston, 1999;Violle et al., 2012), which may not be captured if few individuals are measured. ...
Thermal traits, such as upper and lower critical thermal limits, are vital indicators of the vulnerability of populations and species to environmental change. Thus, accurate estimates of these traits are needed to explain biological patterns and forecast responses to the changing thermal environment. However, many thermal trait studies measure relatively few individuals to estimate traits for whole populations or species.
To ascertain if, and how, sample size affects the accuracy of reported trait means and variances, we applied a subsampling and equivalency testing approach to empirical and simulated trait data to investigate the accuracy of trait estimates relative to sample size and the skew and variance of the trait distribution in the source population.
Simulation results indicated that only 7.9% of the 428 critical thermal limit traits documented in a recent synthesis of thermal trait data reported sufficiently large sample sizes, relative to variance, to ensure confidence in the reported mean trait value with negligible (±0.25°C) error. Greater inter‐individual trait variance in the source population requires a larger number of individuals to be measured to accurately estimate the mean and variance of that trait. This pattern is mitigated somewhat by the tendency of thermal traits to exhibit skew‐normal distributions.
As measurements of few individuals from a population are unlikely to provide accurate estimates of thermal traits, the propensity towards small sample sizes in thermal trait studies is concerning. Macrophysiological syntheses often use these data to describe, explain and predict broad‐scale ecological patterns. Thus, insufficient sample sizes in the original studies could diminish the robustness of these patterns and predictions. For future studies, we recommend that preliminary data be used to estimate trait variance and calculate minimum sample sizes. If small sample sizes are unavoidable, larger error around the measured trait mean must be assumed and accounted for in subsequent analyses.
A free Plain Language Summary can be found within the Supporting Information of this article.
... Semen characteristics, including pH, osmolarity, sperm concentration and motility, have previously been described in freshwater stingray species [9,10], but otherwise little information is available on semen parameters of male ray species. Until recently, many elasmobranch studies have been conducted post-mortem, but it has been recognized that non-lethal sampling should replace these methods [11]. Semen collection, hormone analysis and ultrasound examinations on live specimens are becoming more prevalent for investigating the reproductive biology of elasmobranch species, including the southern stingray [7,12,13]. ...
This study investigated the reproductive biology and sperm cryopreservation of ex situ southern stingrays (Hypanus americanus) by semen collection and characterization and the develop- ment and validation of an enzyme-linked immunoassay for plasma total testosterone. Semen was collected in March and June using a manual massage technique, and the ejaculates were assessed for volume, pH, osmolarity, motility, status (0–5 scale: 0 = no forward progression, 5 = rapid linear progression) and total sperm count. Semen was extended in Hank’s elasmobranch ringer solution containing 10% DMSO, 10% glycerol or 5% glycerol with 5% N-methylformamide and cryopre- served using a conventional freezing method (~−50 ◦C/min) or a modified slow freezing method (~−3 ◦C/min). Body condition was scored from 1–5 and was noted to be low in March (1.93 ± 0.07) due to feeding practices and increased by June (2.93 ± 0.05) after dietary corrections were made. A concomitant increase (p < 0.05) in plasma total testosterone concentration and sperm motility was noted between March (8.0 ± 7.2 ng/mL, 5.71 ± 2.77%) and June (97.3 ± 11.3 ng/mL, 51.4 ± 14.3%). Samples cryopreserved using a modified slow freeze method (~−3 ◦C/min) had higher post-thaw motility and plasma membrane integrity than conventionally cryopreserved samples. Data indicate that southern stingray sperm morphometrics adheres to those of other elasmobranch species and that a slow cooling rate may be an avenue of research to improve southern stingray sperm survival during cryopreservation.
... One limitation of using otoliths to age individuals is the destructive nature of the technique. This is especially relevant when considering age estimation of vulnerable or protected species (Heupel andSimpfendorfer 2010, Hammerschlag andSulikowski 2011). Though the use of non-lethal structures to age fish is growing, there remain drawbacks, for example, scales have been used for estimating the age of young individuals, however their use can lead to underestimation of age among older fish due to outer annuli being less distinct (Muir et al. 2008, Khan et al. 2015, Kumbar and Lad 2016. ...
Knowledge of life-history characteristics and patterns of connectivity are important parameters to fisheries management, especially for species inhabiting hard to reach environments, such as the deep-sea. Golden Tilefish (Lopholatilus chamaeleonticeps) are slow growing, long-lived, demersal species that exhibit a patchy distribution along the continental shelf-edge of the NW Atlantic Ocean. Golden Tilefish create burrows in the clay sediment and maintain high site fidelity. These characteristics suggest the possibility of localized subpopulations across the species’ distribution; an important consideration for the resilience of this species to fishing pressure. My objectives are (1) to estimate age, and model growth of fish captured from a fishery-independent survey and compare these estimates to assessments derived from fishery-dependent data, and (2) to investigate temporal and spatial patterns of habitat connectivity using otolith elemental signatures as natural tags that discriminate subpopulations. Age and growth estimates were consistent consistency with previous assessments and provided an unbiased analysis of the population that can be used for further monitoring. Analysis of elemental profiles indicated subtle spatial differences, suggesting the application for delineating subpopulations. Elemental profiles also varied between years and may represent differing environmental characteristics experienced by the individuals during their pelagic larval stage and subsequent settlement. My thesis contributes age, growth and population connectivity data that will aid in monitoring the stock and development of management decisions
... Therefore, the sharks whose reproductive organs were active had a high contrast effect on these organs, which could be easily differentiated. Ultrasonography is generally applied to confirm the condition of the reproductive organs of elasmobranchs (Carrier et al. 2003;Daly et al. 2007;Whittamore et al. 2010;Hammerschlag and Sulikowski 2011;Sulikowski et al. 2016;Anderson et al. 2018). In the present study, we applied the same protocol as optimal liver CECT scanning for coelomic organs, although the reproductive organs were visualized. ...
The purpose of this study was to determine the optimal imaging protocol for contrast-enhanced computed tomography (CECT) using micro-CT (μ-CT) for the posterior cardinal vein (PCV), dorsal aorta (DA), hepatic portal vein (HPV), kidney, liver, cephalic arteries (CAs), and gills of Cloudy Catsharks Scyliorhinus torazame. Additionally, we examined the availability of CECT screening for the coelomic organs. Different doses of iopamidol (100, 300, 500, and 700 mg iodine [mgI]/kg) were administered intravenously for 20 s in six sharks. The CT scans from the pectoral girdle to the pelvic girdle were performed at 0-600 s after administration. Contrast-enhanced CT imaging of the CAs, gills, and coelomic organs was examined. Assessment of the signal enhancement value revealed that the PCV was easily visualized with all contrast doses at 25 s. The CAs, gills, and DA were visible at a slightly higher dose (CAs and gills: 200 mgI/kg at 40 s; DA: 300 mgI/kg at 50 s). The HPV was obvious at a dose of at least 500 mgI/kg after a 150-s delay. The parenchyma of the kidney had a contrast effect at 300 mgI/kg, 150 s after the contrast effect of the renal portal system disappeared. The liver, which stores a lot of lipids, had poor overall contrast enhancement that was optimized at the highest dose of 700 mgI/kg. Contrast-enhanced CT screening at 700 mgI/kg and 150 s is likely to obtain the optimal imaging of the reproductive organs, such as the ovary, oviducal gland, uterus, and testis. The present findings can be applied not only to clinical practice but also to academic research and education on elasmobranchs in aquariums.
... Research practices that might negatively affect animal welfare can lead to public outrage [43][44][45] and disagreement within the scientific community [44,[46][47][48]. For example, the editors of the journal Biological Conservation reported that they decided to reject several manuscripts for publication on ethical grounds because the authors used lethal methods that the editors considered "unnecessary and inappropriate" [22]. ...
The Earth’s biodiversity is in crisis. Without radical action to conserve habitats, the current rate of species extinction is predicted to accelerate even further. Efficient species conservation requires planning, management, and continuous biodiversity monitoring through wildlife research. Conservation biology was built on the utilitarian principle, where the well-being of species, populations, and ecosystems is given priority over the well-being of individual animals. However, this tenet has been increasingly under discussion and it has been argued that wildlife researchers need to safeguard the welfare of the individual animals traditionally subjected to invasive or lethal research procedures. The 3Rs principles of animal use (Replacement, Reduction, and Refinement) have become the cornerstone of ethical scientific conduct that could minimize the potential negative impact of research practices. One of the obvious strategies to implement the 3Rs in wildlife studies is to use non-invasive or non-lethal research methods. However, in contrast to toxicological or pharmacological research on laboratory animal models, up to now no 3Rs databases or online resources designed specifically for wildlife biologists, ecologists, and conservation managers have been available. To aid the implementation of the 3Rs principles into research on wildlife, I developed an online resource whose structure is outlined in this paper. The website contains a curated database of peer-reviewed articles that have implemented non-invasive or non-lethal research methods that could be used as a guideline for future studies.
... Future studies should consider including larger sample sizes to address such a knowledge gap. Considering the need for non-lethal methodologies in studies with sharks (Hammerschlag and Sulikowski, 2011), toxicology studies could benefit from using animals captured by commercial fisheries. However, considering that many sharks are landed beheaded and eviscerated (Wosnick et al., 2019), sampling of internal organs and blood may be compromised. ...
Contamination by metals is among the most pervasive anthropogenic threats to the environment. Despite the ecological importance of marine apex predators, the potential negative impacts of metal bioaccumulation and biomagnification on the health of higher trophic level species remains unclear. To date, most toxicology studies in sharks have focused on measuring metal concentrations in muscle tissues associating human consumption and food safety, without further investigating potential impacts on shark health. To help address this knowledge gap, the present study evaluated metal concentrations in the gills, muscle, liver, and rectal gland of coastal sharks opportunistically sampled from Brazilian waters and tested for potential relationships between metal bio-accumulation and general shark health and homeostatic balance metrics. Results revealed high metal concentrations in all four tissue types, with levels varying in relation to size, sex, and life-stage. Metal concentrations were also associated with serum biomarkers (urea, lactate, ALT, triglycerides, alkaline phosphatase, and phosphorus) and body condition, suggesting potential negative impacts on organismal health.
... There is a pressing need to move away from lifehistory based estimates of M to more direct estimates derived from species-specific data. Electronic tagging is an important source of information on movement, habitat associations and survival of large pelagic fishes (Hammerschlag and Sulikowski, 2011;Hazen et al., 2012), and provides an opportunity to directly estimate natural mortality from survival data (e.g., Benoît et al., 2015Benoît et al., , 2020a. Nonetheless the substantial cost associated with archival tags still constrains sample sizes (Hazen et al., 2012) and poses a particular challenge for reliable estimation of M for long-lived species. ...
Accurately characterizing the biology of a pelagic shark species is critical when assessing its status and resilience to fishing pressure. Natural mortality (M) is well known to be a key parameter determining productivity and resilience, but also one for which estimates are most uncertain. While M can be inferred from life history, validated direct estimates are extremely rare for sharks. Porbeagle (Lamna nasus) and shortfin mako (Isurus oxyrinchus) are presently overfished in the North Atlantic, but there are no directed fisheries and successful live release of bycatch is believed to have increased. Understanding M, post-release mortality (PRM), and variables that affect mortality are necessary for management and effective bycatch mitigation. From 177 deployments of archival satellite tags, we inferred mortality events, characterized physiological recovery periods following release, and applied survival mixture models to assess M and PRM. We also evaluated covariate effects on the duration of any recovery period and PRM to inform mitigation. Although large sample sizes involving extended monitoring periods (>90 days) would be optimal to directly estimate M from survival data, it was possible to constrain estimates and infer probable values for both species. Furthermore, the consistency of M estimates with values derived from longevity information suggests that age determination is relatively accurate for these species. Regarding bycatch mitigation, our analyses suggest that juvenile porbeagle are more susceptible to harm during capture and handling, that keeping lamnid sharks in the water during release is optimal, and that circle hooks are associated with longer recovery periods for shortfin mako.
... The traditional approach of dissection an animal's digestive tract is an efficient and thorough method, as it allows the collection of the entire amount of ingested prey items (Bangley et al., 2013). While dissections can be useful for the investigation of small-bodied sharks with no urgent conservation concern (Bethea et al., 2004) or for commercially landed species (McElroy et al., 2006;Biton Porsmoguer et al., 2014), this method is not applicable for mobile and large-bodied sharks with conservation concern, although this is contentious (Heupel & Simpfendorfer, 2010;Hammerschlag & Sulikowski, 2011). ...
In areas of sympatry, closely related and morphologically similar species are expected to occupy different ecological niches in order to avoid competition. However, without knowledge on competitive abilities (e.g. dominance hierarchies) and population characteristics (e.g. growth rates, fitness traits), the origin and the potential effects of niche pattern (segregation and overlap) are unknown. I found compelling evidence that juvenile blacktip reef sharks Carcharhinus melanopterus and juvenile sicklefin lemon sharks Negaprion acutidens from St. Joseph Atoll, Seychelles exhibit fine-scale segregation patterns as a means to avoid competition. In contrast, slight differences in population characteristics were more likely to be caused by prey availability, intraspecific competition, and anthropogenic impacts. This thesis highlights the need for multi-disciplinary investigations to unveil the underlaying mechanisms of coexistence.
... The seasonal mismatches in peak catch rates and detections of adult males and adult females also suggests that Biscayne Bay is not a mating ground. To further explore Biscayne Bay's potential as a C. leucas gestation ground, future studies could measure serum concentrations of different reproductive hormone levels in this species (Manire et al. 1995) combined with ultrasonography (Hammerschlag and Sulikowski 2011) to determine seasonal variation in reproductive state in female C. leucas as a non-lethal method to test this hypothesis. It is possible that sharks' connectivity to regions outside of Biscayne Bay is associated with increased foraging opportunities elsewhere. ...
Understanding the movement ecology of marine species is important for conservation management and monitoring their responses to environmental change. In this study, adult and subadult bull sharks (Carcharhinus leucas; n = 16) were acoustically tagged in Biscayne Bay, Florida (USA), where they were tracked locally via an array of 40 passive acoustic receivers, as well as regionally via cooperative acoustic telemetry networks, with individuals tracked up to 4.5 years. Detection data were used to assess philopatry, regional connectivity, and environmental correlates of shark habitat use. Spatial range varied per individual; however, most individuals displayed high residency to Biscayne Bay, exhibiting strong philopa-tric behavior to the tagging area. A generalized linear mixed model revealed a seasonal pattern in habitat use, with mature females displaying high residency in Biscayne Bay during the colder dry season (November to February) and lower residencies during the warmer wet season (June to October). These seasonal patterns were supported by catch data from long-term fishery-independent shark surveys in the study area. During summer months when residencies of C. leucas declined in Biscayne Bay, their residencies increased in other regions (e.g., Florida Gulf Coast), demonstrative of seasonal migrations. Connectivity between areas of high use (Biscayne Bay and Florida Gulf Coast) was demonstrated by some individuals traveling between these areas. Results from generalized additive mixed models suggest that these movement patterns could be partially driven by seasonal changes in environmental variables as well as an individual's life stage, including reproductive status.
... invasive methods such as stomach eversion and gastric lavage, or lethal sampling (Barnett et al., 2010;Bornatowski et al., 2014;Cortés & Gruber, 1990;Matich et al., 2020;Papastamatiou et al., 2006;Rosende-Pereiro et al., 2019;Trystram et al., 2017). These methods are necessary but undesirable for threatened and/or protected species (Hammerschlag & Sulikowski, 2011;Heupel & Simpfendorfer, 2010). Moreover, morphological stomach content analysis is labour-intensive, requires extensive taxonomic knowledge and lacks resolution as prey items are often digested, making them difficult or impossible to identify. ...
Animal dietary information provides the foundation for understanding trophic relationships, which is essential for ecosystem management. Yet, in marine systems, high-resolution diet reconstruction tools are currently under-developed. This is particularly pertinent for large marine vertebrates, for which direct foraging behaviour is difficult or impossible to observe and, due to their conservation status, the collection of stomach contents at adequate sample sizes is frequently impossible. Consequently, the diets of many groups, such as sharks, have largely remained unresolved. To address this knowledge gap, we applied metabarcoding to prey DNA in faecal residues (fDNA) collected on cotton swabs from the inside of a shark's cloaca. We used a previously published primer set targeting a small section of the 12S rRNA mitochondrial gene to amplify teleost prey species DNA. We tested the utility of this method in a controlled feeding experiment with captive juvenile lemon sharks (Negaprion brevirostris) and on free-ranging juvenile bull sharks (Carcharhinus leucas). In the captive trial, we successfully isolated and correctly identified teleost prey DNA without incurring environmental DNA contamination from the surrounding seawater. In the field, we were able to reconstruct high-resolution teleost dietary information from juvenile C. leucas fDNA that was generally consistent with expectations based on published diet studies of this species. While further investigation is needed to validate the method for larger sharks and other species, it is expected to be broadly applicable to aquatic vertebrates and provides an opportunity to advance our understanding of trophic interactions in marine and freshwater systems.
... If generalizable across species, our findings have the potential to reduce the number of animals sacrificed for estimating gill surface area. Further, the ethics and justification of lethal sampling have been called into question, especially for data-poor and threatened species (Heupel and Simpfendorfer, 2010;Hammerschlag and Sulikowski, 2011;Sloman et al., 2019). Thus, it is important to re-evaluate lethal sampling practices and determine if it is possible to devise and pursue non-lethal methods of inference. ...
Metabolically important traits, such as gill surface area and metabolic rate, underpin life histories, population dynamics and extinction risk, as they govern the availability of energy for growth, survival and reproduction. Estimating both gill surface area and metabolic rate can be challenging, especially when working with large-bodied, threatened species. Ideally, these traits, and respiratory physiology in general, could be inferred from external morphology using a faster, non-lethal method. Gill slit height is quick to measure on live organisms and is anatomically connected to the gill arch. Here, we relate gill slit height and gill surface area for five Carcharhiniform sharks. We compared both total and parabranchial gill surface area to mean and individual gill slit height in physical specimens. We also compared empirical measurements of relative gill slit height (i.e. in proportion to total length) to those estimated from field guide illustrations to examine the potential of using anatomical drawings to measure gill slit height. We find strong positive relationships between gill slit height and gill surface area at two scales: (i) for total gill surface area and mean gill slit height across species and (ii) for parabranchial gill surface area and individual gill slit height within and across species. We also find that gill slit height is a consistent proportion of the fork length of physical specimens. Consequently, relative gill slit height measured from field guide illustrations proved to be surprisingly comparable to those measured from physical specimens. While the generality of our findings needs to be evaluated across a wider range of taxonomy and ecological lifestyles, they offer the opportunity that we might only need to go to the library and measure field guide illustrations to yield a non-lethal, first-order approximation of the respiratory physiology of sharks.
... Typically, scientific population censuses of sharks are made by utilizing fisheries-dependent data, such as catch or bycatch data (e.g., Baum et al., 2003;Carlson et al., 2012;Ferretti et al., 2008) or fisheries independent data that may still involve high mortality sampling techniques, such as with gillnets (Froeschke et al., 2010;e.g., Ward-Paige et al., 2015) or trawls (Ferretti et al., 2010). Some aim to lower mortality during sampling (Hammerschlag and Sulikowski, 2011), especially where tags for mark-recapture or tracking studies are being used (Speed et al., 2011). However, in many areas where lethal sampling is illegal or unacceptable, such as on coral reefs, coastal areas near tourist sites, and marine protected areas, non-lethal sampling is often sought. ...
Many marine animals around the world are threatened by a variety of anthropogenic activities, yet there is often a paucity of data to monitor patterns in abundance and distribution or to evaluate human interventions. The new citizen science program eOceans helps to fill this gap by gathering observations of various marine animals from worldwide ocean explorers. In 2012, a dedicated Thailand-wide census of sharks, and other animals, began as collaboration between eOceans scientists and the dive tourism industry. Using the observations from 9,524 dives (9,357 hours underwater) logged by >169 divers on 153 sites, we describe the spatial and temporal patterns of sharks in coastal Thailand. A total of 12 shark species were encountered, most commonly (67%) as individuals, and were observed on 11% of all dives, on 59% of sites, in all months and years. The two most frequently encountered species were blacktip reef ( Carcharhinus melanopterus ) and leopard sharks ( Stegostoma fasciatum ). Many species had peak encounter rates in summer, but aggregated in various seasons in different years. Mating events and nursery sites were observed rarely, and only for blacktip reef and whitetip reef ( Triaenodon obesus ) sharks. These results could be of value to species-or region-specific biologists, ecologists and fisheries scientists, as well as to managers and policy makers that could use the findings to monitor future trends and prioritize conservation strategies. Moreover, this study highlights the value that collaborative eOceans citizen science projects could have in support of marine science, management and conservation efforts worldwide.
... Scaled image measurements of both traditional and geometric morphometrics have been previously used to respectively acquire linear body dimensions and to infer variation in morphology and ecology in marine organisms [47][48][49][50] . This method therefore represents a viable non-lethal alternative for collecting measurement data, which have been proposed as urgently needed for the declining populations of large predatory sharks 51 . The life stage of each individual was also recorded (see Supplementary information for more details). ...
Inferring the size of extinct animals is fraught with danger, especially when they were much larger than their modern relatives. Such extrapolations are particularly risky when allometry is present. The extinct giant shark †Otodus megalodon is known almost exclusively from fossilised teeth. Estimates of †O. megalodon body size have been made from its teeth, using the great white shark (Carcharodon carcharias) as the only modern analogue. This can be problematic as the two species likely belong to different families, and the position of the †Otodus lineage within Lamniformes is unclear. Here, we infer †O. megalodon body dimensions based on anatomical measurements of five ecologically and physiologically similar extant lamniforms: Carcharodon carcharias, Isurus oxyrinchus, Isurus paucus, Lamna ditropis and Lamna nasus. We first assessed for allometry in all analogues using linear regressions and geometric morphometric analyses. Finding no evidence of allometry, we made morphological extrapolations to infer body dimensions of †O. megalodon at different sizes. Our results suggest that a 16 m †O. megalodon likely had a head ~ 4.65 m long, a dorsal fin ~ 1.62 m tall and a tail ~ 3.85 m high. Morphometric analyses further suggest that its dorsal and caudal fins were adapted for swift predatory locomotion and long-swimming periods.
... How these changes in growth rate translate to first dorsal fin shape has not yet been quantified, although some morphological differences are likely between adults and juveniles [50]. These higher growth rates may also encapsulate the SPOT transmitter within animal tissue, preventing wet-dry sensors from operating normally, or alternatively may eject the transmitter as a foreign body [81,82]. ...
The tiger shark (Galeocerdo cuvier) is globally distributed with established coastal and open-ocean movement patterns in many portions of its range. While all life stages of tiger sharks are known to occur in the Gulf of Mexico (GoM), variability in habitat use and movement patterns over ontogeny have never been quantified in this large marine ecosystem. To address this data gap we fitted 56 tiger sharks with Smart Position and Temperature transmitting tags between 2010 and 2018 and examined seasonal and spatial distribution patterns across the GoM. Additionally, we analyzed overlap of core habitats (i.e., 50% kernel density estimates) among individuals relative to large benthic features (oil and gas platforms, natural banks, bathymetric breaks). Our analyses revealed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Presumably sub-adult and adult sharks achieved significantly higher movement rates and used off-shelf deeper habitats at greater proportions than juvenile sharks, particularly during the fall and winter seasons. Further, female maximum rate of movement was higher than males when accounting for size. Additionally, we found evidence of core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern (i.e., shelf-edge banks) during cooler months, particularly by females, as well as 2,504 oil and gas platforms. These data provide a baseline for future assessments of environmental impacts, such as climate variability or oil spills, on tiger shark movements and distribution in the region. Future research may benefit from combining alternative tracking tools, such as acoustic telemetry and genetic approaches, which can facilitate long-term assessment of the species’ movement dynamics and better elucidate the ecological significance of the core habitats identified here.
Over the past 4 decades there has been a growing concern for the conservation status of elasmobranchs (sharks and rays). In 2002, the first elasmobranch species were added to Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Less than 20 yr later, there were 39 species on Appendix II and 5 on Appendix I. Despite growing concern, effective conservation and management remain challenged by a lack of data on population status for many species, human−wildlife interactions, threats to population viability, and the efficacy of conservation approaches. We surveyed 100 of the most frequently published and cited experts on elasmobranchs and, based on ranked responses, prioritized 20 research questions on elasmobranch conservation. To address these questions, we then convened a group of 47 experts from 35 institutions and 12 countries. The 20 questions were organized into the following broad categories: (1) status and threats, (2) population and ecology, and (3) conservation and management. For each section, we sought to synthesize existing knowledge, describe consensus or diverging views, identify gaps, and suggest promising future directions and research priorities. The resulting synthesis aggregates an array of perspectives on emergent research and priority directions for elasmobranch conservation.
The study of the reproductive aspects of chondrichthyans through the analysis of steroid hormones has been carried out for more than five decades in several species around the world. This scientific knowledge constitutes the basis of the reproductive endocrinology of chondrichthyans, which has provided information regarding their sexual maturation, gametogenesis, mating seasons, gestation periods, and parturition. The present review summarises the existing literature on steroid hormones in chondrichthyan reproduction and identifies future research directions addressing critical knowledge gaps in the reproductive physiology of this taxon. A total of 59 peer reviewed scientific papers from 1963 to 2020 were reviewed and the following parameters analysed: species, steroid hormones, biological matrix, field sampling (year, location), and methodology (assays, sample size, precision, and recoveries). We provided a summary of the methods, biological matrices, and the functions of up to 19 hormones on the biology of 34 species of chondrichthyans that have been analysed to date. The majority of the studies used radioimmunoassay as the main methodology (76.3%; n = 45/49); while the most frequent biological matrix used was plasma (69.5%; n = 41/49). A Kernel’s heat map was generated to present the scientific effort according to geographic location and evidenced a lack of research in high biodiversity areas for chondrichthyans worldwide. The implications of the study of steroid hormones for the conservation of chondrichthyans are discussed, as only 2.9% of the species of this group have been analysed and most of the scientific effort (93.2%; n = 55/59 papers) has focused on the analysis of less than six hormones.
The reproductive biology of a pride of lions (Panthera leo) was studied on the 8500 ha Karongwe Game Reserve from 1999 to 2005. Over this period, the pride consisted of between four and 11 lions with a paired coalition of adult males during the first three years and a single adult male for the next three years. We recorded shorter than normal interbirth intervals, high birth rates of 1.3 cubs/lioness/year, very high cub survival rates, and subadults leaving the pride at young ages. This translated into substantially faster growth rates than are typical in large lion populations in ecologically similar circumstances such as Kruger National Park, but are similar to those of lions in Serengeti National Park. These demographic characteristics were probably induced initially by a lack of intense intraspecific competition and high prey availability, but population stability was maintained through the removal of young subadults by management. Interestingly, variability in conception rates between lionesses resulted in lower growth rates than have been found in other similar reintroduced lion populations. These demographic traits characterize many of the small reintroduced lion populations, and call for appropriate management to avoid the consequences of high predator densities.
It is important to understand the ages, growth characteristics, maturation processes, and longevity of fishes to assess their current population status and to predict how their populations will change in time (Ricker, 1975; Cailliet et al., 1986b). Fishery biologists have used age, length, and weight data as important tools for their age-based population models. Especially important are details about growth and mortality rates, age at maturity, and life span (Ricker, 1975; Cortés, 1997). Over the past several decades, it has become obvious that fisheries for chondrichthyan fishes have not been easily sustainable. In 1974, Holden suggested that these fishes had life histories that made them vulnerable to overfishing. Included in the characteristics he cited were slow growth, late age at maturity, few offspring, and lengthy gestation periods. Since then, fishing pressure on elasmobranchs, both as directed and as bycatch fisheries (and discards) has increased (Bonfil, 1994; Casey and Myers, 1998; Stevens et al., 2000; Baum et al., 2003), stimulating many studies on many important aspects of their life histories, such as age, growth, and reproduction.
Age and growth estimates for the blue shark, Prionace glauca, were derived from 411 vertebral centra, and 43 tag-recaptures collected in the North Atlantic. The vertebrae of two oxytetracycline-injected recaptures support an annual spring deposition of growth rings in the vertebrae in sharks up to 192 cm FL . Males and females were aged to 16 and 15 ye ars, respectively. Both sexes grew similarly to age seven when growth rates decreased in males and remained constant in females . Growth rates from tag-recaptures agreed with those derived from vertebral annuli for smaller sharks but appeared overestimated for larger sharks. Von Bertalanffy growth parameters derived from vertebral length-at-age data are L∞ = 282 cm FL, K = 0.18, and to = -1.35 for males and L∞ = 310 cm FL, K = 0.13, and to = - 1.77 for females. The species grows faster and has a shorter life span than previously reported in these waters.
Pop-up satellite archival tags (PSATs) were used to study the migration patterns and habitat preference of 56 white sharks tagged off Guadalupe Island, Mexico, between 2000 and 2008. Nine tags were recovered, providing 1021 d of high resolution (2 min) archival data. Two individual sharks were tagged in consecutive years, providing 2 yr of tracking data for each individual. White sharks were found to make long-range, seasonal migrations from Guadalupe Island to an offshore pelagic habitat, sometimes traveling as far west as the Hawaiian Islands. The pelagic region inhabited by Guadalupe Island white sharks corresponds with that reported for sharks tagged off central California; thus we have termed it the Shared Offshore Foraging Area (SOFA). Sharks spent at least 5 mo off Guadalupe Island before beginning their migration around 15 February on average (earliest 21 December, latest 5 May). They traveled through a migration corridor in an average time of 16 d at an average speed of 3.2 km h(-1) and remained in the SOFA for an average duration of 140 d. Males and females began their offshore migrations around the same time and traveled to the same area, but males were found to return to Guadalupe Island on average around 22 July (earliest 15 July, latest 30 July), while females remained in the SOFA into early autumn. Diving profiles of sharks in the SOFA strongly suggest feeding behavior; however, the targeted prey species are unknown at this time.
Bands on the external surface of the second dorsal-fin spine proved to be a novel method of estimating the age and growth of Centroselachus crepidater. Bands that followed the shape of the spine base were enhanced with an alizarin red derivative. Internal bands in spine cross sections were also examined. The number of both external and internal bands increased with animal size, although most spines had more external than internal bands. External bands were more reliable and were assumed to be annuli. The rate of band formation differed after five bands had been formed, and internal bands ceased forming after 30 years. Females to 54 years old and males to 34 years old were examined. Maturity occurred over a wide age range, with estimates of 20 years for females and 9 years for males. The youngest pregnant female was 27 years old. The Francis reparameterized von Bertalanffy growth model found similar growth for males and females, and the von Bertalanffy equations were L t = 96.12(1 – e(–0.072(t+6.13))) for females and Lt = 73.22(1 – e(–0.141(t+2.99))) for males.
Age and growth of the sandbar shark (Carcharhinus plumbeus) were determined from tag and recapture data covering a 26-yr period (1964–90). Results were compared with previously published age and growth estimates based primarily on rings in vertebrae. Recent long-term tag returns suggest that the sandbar shark grows much slower than previously proposed and may take nearly 30 yr to reach maturity. Revised von Bertalanffy parameters (sexes combined) are L∞ = 186, k = 0.046, and t0 = −6.45. The limitations of ageing elasmobranchs solely from rings in vertebrae and the need for validating rings in hardparts of fishes are discussed.
Assigning ages to lions (Panthera leo) requires the use of subjective and objective criteria, and is useful for conservation decision-making in that age distributions can be defined from which demographic profiles can be extracted. We collated all age assignment criteria and found that a constraint of most objective criteria is that they require Immobilized or dead specimens to measure. Furthermore, nearly all criteria used lions with assumed ages to construct relationships or narrative descriptions. We show that digital photogrammetry provides digitally-derived measures of shoulder heights similar to that of linearly derived measures. In addition, such shoulder heights did not differ between captive and free ranging lions, or between different regions in Africa. Variation in shoulder height is primarily associated with sex-specific age. Age, using the von Bertalanffy growth curve, explained 92% and 97% of the variation in female and male shoulder height, a skeletal measure not strongly affected by resource availability. Simulations suggest that age assignment is relatively accurate for females and males with shoulder heights up to 70 cm and 95 cm, respectively. Thus for lions younger than two years of age objective criteria gives most precise estimates, while subjective criteria are more suitable for older lions. Key words: African lion, age assignment, growth, shoulder height.
Food web relationships in marine systems have traditionally been defined through stomach content analysis, but biochemical techniques have recently emerged to validate and broaden temporal diet patterns. Stable isotope analysis has become a practical tool for evaluating these relationships in aquatic systems; however, routine sampling of muscle tissue captures only part of the trophic information available from each animal. We compared δ 15 N and δ 13 C values among liver, muscle and cartilage in the blue shark Prionace glauca, shortfin mako Isurus oxyrinchus, and common thresher Alopias vulpinus from the northwest Atlantic to show how multiple-tissue sampling captured feeding relationships which would have been invisible to muscle tissue alone. Specifically, we demonstrated evidence of a cephalopod to bluefish Pomatomus saltatrix diet switch in the short- fin mako in spring, and found that the blue shark and common thresher have consistent diets throughout the year. We concluded that consistency observed among stable isotope values in multi- ple tissues implied that the fish were in steady-state with the isotope ratios of their diet and that multiple tissues should be used in trophic assessments of large pelagic fishes. Further experiments to quantify the turnover of stable isotopes in different tissues and species are needed to improve the accuracy of stable-isotope analyses .
The shortfin mako, Isurus oxyrinchus, is caught in the eastern North Atlantic as a regular bycatch of the surface-drift longline fishery, mainly directed towards swordfish, Xiphias gladius. Stomachs of 112 shortfin mako sharks, ranging in size from 64cm to 290cm fork length, showed teleosts to be the principal component of the diet, occurring in 87% of the stomachs and accounting for over 90% of the contents by weight. Crustaceans and cephalopods were also relatively important in this species’ diet, whereas other elasmobranchs were only present in lower percentages. Meal overlap was observed in half of the sampled sharks. No clear trend of prey size selectivity was found, despite smaller individuals seeming incapable of pursuing larger and faster prey. The retention of small prey was also observed in the diet of all sizes of shark. Seasonality in food habits was in accordance with the current availability of food items. The observed vacuity index of 12% is comparable to foraging ecology studies using gillnetting and appears not to be influenced by baited longline gear. Morphological relationships of the digestive system might add important information to the foraging ecology studies and to ecosystem modelling.
The tiger shark (Galeocerdo cuvier) is the largest shark in the family Carcharhinidae and the only carcharhinid with aplacental viviparous (ovoviviparous) reproduction.
Despite its size and prevalence, many details of tiger shark reproductive biology are unknown. Size at maturity and litter
size have been reported by several authors, but a lack of large numbers of pregnant females has made it difficult to determine
gestation period, seasonality, and timing of the female reproductive cycle. Here we analyze data from shark control program
fishing and incidental catches in Hawaii (n=318) to construct the most complete picture of tiger shark reproduction to date. Males reached maturity at approximately
292cm total length (TL) based on clasper calcification, whereas females matured between 330 and 345cm TL based on oviducal
gland and uterus widths. Litter sizes ranged from 3 to 57 with a mean of 32.6 embryos per litter. Data from 23 litters from
various months of the year indicate that tiger sharks are usually 80–90cm TL at birth, and that the gestation period is 15–16
months. Mating scars were observed in January–February and sperm is presumably stored for 4–5months until ovulation takes
place in May–July. Gestation begins in June–July and pups are born in September–October of the following year. Our data suggest
that female tiger sharks in Hawaii give birth only once every three years. This could have major implications for conservation
and management of this species, as it suggests that tiger shark fecundity is 33% lower than previously thought. This could
greatly reduce the ability of this species to rebound from fishing pressure.
Satellite telemetry studies of 20 adult and sub-adult white sharks (360–530cm estimated total length (TL)) in the eastern
North Pacific during 1999–2005 revealed long distance seasonal migrations from the coast of California to an offshore focal
area 2,500km west of the Baja Peninsula, as well as the Hawaii Islands. Three tags were recovered allowing detailed behavioral
analyses, including one shark’s migration cycle from the coast to the offshore focal area and back. While near pinniped rookeries
in autumn and winter, sharks avoided the surface and used water to 50m depth, consistent with a silhouette-based hunting
strategy. Offshore migrations were initiated during November–March and followed periods of decreasing pinniped abundance.
Migrations were highly directed, taking 23±5days to reach the offshore focal area along similar paths among sharks and
years, defining a migration corridor. Sharks exhibited a broad depth distribution (0–644m) in the offshore focal area, and
remained there for up to 167days during spring and summer, though primary productivity and fishery data suggest that forage
resources are scarcer there than in other regions of the eastern North Pacific. Archival data from one shark revealed intensive
oscillatory movements while in the offshore focal area, a behavior that may be related to foraging or mating. Sharks traveling
to Hawaii remained near the islands up to 122 days, potentially feeding on pelagic fishes and marine mammals that concentrate
around the islands.
Mark-recapture techniques can be used to estimate white shark (Carcharodon carcharias) population abundance. These frameworks are based on assumptions that marks are conserved and animals are present at the
sampling location over the entire duration of the study. Though these assumptions have been validated across short-time scales
for white sharks, long-term studies of population trends are dependent on these assumptions being valid across longer periods.
We use 22years of photographic data from aggregation sites in central California to support the use of dorsal fin morphology
as long-term individual identifiers. We identified five individuals over 16–22years, which support the use of dorsal fins
as long-time individual identifiers, illustrate strong yearly site fidelity to coastal aggregation sites across extended time
periods (decades), and provide the first empirical validation of white shark longevity >22years. These findings support the
use of fin morphology in mark-recapture frameworks for white sharks.
Information regarding sexual maturity and reproductive cycles in skates has largely been based on gross morphological changes
within the reproductive tract. While this information has proved valuable in obtaining life history information, it also necessitates
sacrificing the skates to obtain this data. In contrast, few studies have used circulating steroid hormones to establish when
these batoids become reproductively capable or for the determination of reproductive cyclicity. This study summarizes our
current knowledge of hormonal analyses in determining skate reproductive status and offers information that suggests analysis
of circulating steroid hormone concentrations provide a means to determine size at sexual maturity and asses reproductive
cycles without the need to sacrifice the skate.
This study provides the first published age estimates for the roughtail skate, Bathyraja trachura. Age and growth characteristics of B. trachura, a poorly-known deepwater species, were determined from samples collected along the continental slope of the contiguous western
United States. A new maximum size was established at 91.0cm TL. Age was determined using a traditional structure (vertebral
thin sections) with widespread application on multiple skate species and a non-lethal structure (caudal thorns) recently used
for age analysis on skate species. Caudal thorns were determined not to be a useful ageing structure for this species based
on poor precision and significantly lower age estimates when compared to age estimates from vertebral thin sections. The best
model for describing growth of B. trachura was the two parameter VBGF, assuming annual vertebral band deposition and using length-at-age data. Although females grew
slower and reached a larger maximum size than males, their growth was not statistically different (ARSS; P=0.90); therefore, data were pooled (L∞=99.38, k=0.09). Annual band deposition was found to be a reasonable assumption for this species, but has yet to be validated.
The maximum age estimated for B. trachura was 20years for males and 17years for females using vertebral thin sections.
In previous literature it was proposed that Atlantic sharpnose sharks, Rhizoprionodon terraenovae, from the western Atlantic Ocean (WAO) population exhibited differences in their reproductive timing when compared to the
northern Gulf of Mexico (GOM) population. The objective of the current study was to examine the reproductive cycle of mature
male sharpnose sharks from the northern GOM population. Plasma testosterone (T) and estradiol (E2) were measured from 76 mature male sharpnose sharks sampled from 1999 to 2001, and the gonadosomatic index (GSI) was determined
for 53 additional mature males sampled from 2007-2008. Plasma T, E2, and GSI exhibited similar cycles with peak values occurring in late spring (April/May) and lowest values occurring during
the summer. These results suggest that male sharpnose sharks in the northern GOM are reproductively active one to two months
earlier than previously reported, which now brings them into synchrony with the WAO population. Interestingly, this shift
in reproductive timing corresponds with a 3.0°C (13.4%) increase in spring sea surface temperature (SST) from the Mississippi
Sound over a 29year period, which could translate into GOM male sharpnose sharks becoming reproductively active earlier in
the year thus explaining the late spring peak in GSI.
KeywordsAtlantic sharpnose shark-Testosterone-Estradiol-Gonadosomatic index-Reproductive cycle
Visual identification of naturally acquired marks has been a popular if subjective method of animal identification and population
estimation over the last 40years. Molecular genetics has also independently developed objective individual marking techniques
during the same period. Here, we assess the concordance of individual great white shark (Carcharodon carharias) dorsal fin recognition and identification, using seven microsatellite loci as the independent unbiased arbiter, over a period
of 5years. As a monitoring technique, fin photographs offer a very good individual identification key for white sharks over
a relatively short period of time (5years), matching with genetic data in about 85% of cases, whilst caution and a continuously
updated database is required for animal recognition over a longer period.
Resource utilization by nine abundant piscivores from a diverse tropical fish assemblage was examined over the course of a year. All nine species exhibited peak reproduction during the early wet season and a similar sequence of size-dependent shifts from a diet composed primarily of microcrustacea, to aquatic insects, and finally fishes. Three piranha species specialized on fish fins, particularly at subadult size classes (SL 30–80 mm). Gradual dessication of the floodplain during the transition season was associated with fish growth, increased fish density, and decreased aquatic primary productivity and availability of invertebrate prey. Based on 118 resource categories, average pairwise diet overlap was low during all three seasons: wet, transition, and dry. Of 72 species pairings, only one pair of fin-nipping piranhas exhibited high overlap simultaneously on three niche dimensions: food type, food size, and habitat. Adults of two species, a gymnotid knifefish and pimelodid catfish, were largely nocturnal. Patterns of habitat utilization indicate that piranhas may restrict diurnal use of the open-water region by other piscivores. Collective diet overlap of individual piscivore species with the other eight feeding guild members and collective overlaps with the entire fish community each revealed two basic seasonal trends. Four species that showed an early switch to piscivory also showed a high degree of diet separation with both the guild and community at large on a year-round basis. The five remaining species showed lowest collective diet overlaps during the transition season when availability of invertebrates was reduced and fish densities were maximal. Whereas predation may play a role in habitat separation, diffuse competition for food resources during the approximately four-month transition season probably is the principal factor yielding patterns of diet specialization.
The decline of top oceanic predators (TOPs), such as great sharks, and worldwide erosion of the marine food web is among the most important functional changes in marine systems. Yet, even though human pressures on sharks are one of the most important factors in the collapse of TOPs, the social science of shark fishing has not kept pace with the biophysical science. Such a gap highlights the need for a marine social science, and this paper uses the case of sharks to illustrate some advances that a coherent marine social science community could bring to science and sustainability, and calls for the development of this new field. Social oceanography is proposed as a “discursive space” that will allow multiple social science and humanities disciplines to holistically study and bring insight to a diverse but essential community. Such a community will not provide answers for the physical sciences, but it will add a new understanding of the contingencies that riddle social behavior that ultimately interact with marine systems. Such a field should reflect the broad and diverse approaches, epistemologies, philosophies of science and foci that are in the human disciplines themselves. Social oceanography would complete the triumvirate of biological and physical oceanography where human systems profoundly impact these other areas. This paper tests the theory that institutional rules are contingent on social priorities and paradigms. I used content analysis of all available (1995–2006) State of the World Fisheries and Aquaculture (SOFIA) reports from the United Nations Food and Agricultural Organization (FAO) to measure the symbolic behavior—i.e., what they say—as an indication of the value of sharks in world fisheries. Similar tests were also performed for marine journals and the Convention on Migratory Species of Wild Animals to corroborate these findings. Then, I present an institutional analysis of all international capacity building and regulatory institutions as they pertain to sharks. We find that sharks are not a high priority compared to other fisheries; and, amongst issue areas, ecological concerns are overshadowed by a paradigm of economism (economic values are demonstrated above all others). Further, sharks have no global binding institutions for conservation, and only new and problematic rules at regional levels. Consequently, human pressures on sharks are partially explained through social marginalization that legitimizes permissive international rules that: (1) have limited scope of authority, (2) provide little-to-no active management of sharks, (3) have important enforcement problems, and (4) are generally not reinforced with National Plans of Action demonstrating a lack of commitment at both national and international scales. Thus, active management of shark populations is nearly non-existent meanwhile pressures on sharks, such as through finning, have increased in the last 20 years and there is strong evidence that many shark species are in decline and may not be able to recover. This paper concludes by arguing that biological oceanography of sharks is fundamentally linked to human dimensions, and, therefore, theories and systematic study of human dimensions in oceanography are crucial to provide more comprehensive understanding of complete social-marine systems.
The reproductive biology of a single pride of lions (Panthera leo) was studied on the 8500 ha Karongwe Game Reserve from 1999-2005. Over this period the pride consisted of between 4-11 lions, with a paired coalition of adult males during the first three years, and a single adult male for the next three years. We recorded shorter than normal interbirth intervals, high birth rates of 1.3 cubs/lioness/year, very high cub survival rates, and subadults leaving the pride at young ages. This translated into substantially higher growth rates that are typical in large lion populations in ecologically similar circumstances such as Kruger National Park, but are similar to those of lions in Serengeti National Park. These demographic characteristics were probably induced initially by a lack of intense intraspecific competition and high prey availability, but were maintained through the removal of young subuadults by management. Combined these result in very high growth rates that continue to be problematic for management. Interestingly, variability in conception rates between lionesses resulted in lower growth rates than have been found in other similar reintroduced lion populations. These demographic traits characterise many of the small re-introduced lion populations in South Africa, and call for appropriate management to avoid the consequences of high predator densities.
Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.
Blood gas, pH, and lactate data are often used to assess the physiological status and health of fish and can often be most valuable when blood samples are analyzed immediately after collection. Portable clinical analyzers allow these measurements to be made easily in the field. However, these instruments are designed for clinical use and thus process samples at 37 degrees C. A few studies have validated the use of portable clinical analyzers for assessing blood gases and acid-base profiles in teleosts, but equivalent data are not available for elasmobranchs. We therefore examined the relationship of blood gas, pH, and lactate values measured with an i-STAT portable clinical analyzer with those measured using standard laboratory blood gas (thermostatted to 25 degrees C) and lactate analyzers in samples taken from three species of carcharhiniform sharks. We found tight correlations (r2 > 0.90) between these methods for pH, pO2, pCO2, and lactate level values. We thus developed species-specific equations for converting blood values measured with an i-STAT portable clinical analyzer to those taken at 25 degrees C. Additional studies need to address a wider range of temperatures and elasmobranch species.
The decline of sharks in the global oceans underscores the need for careful assessment and monitoring of remaining populations. The northeastern Pacific is the home range for a genetically distinct clade of white sharks (Carcharodon carcharias). Little is known about the conservation status of this demographically isolated population, concentrated seasonally at two discrete aggregation sites: Central California (CCA) and Guadalupe Island, Mexico. We used photo-identification of dorsal fins in a sequential Bayesian mark-recapture algorithm to estimate white shark abundance off CCA. We collected 321 photographs identifying 130 unique individuals, and estimated the abundance off CCA to be 219 mature and sub-adult individuals ((130, 275) 95% credible intervals), substantially smaller than populations of other large marine predators. Our methods can be readily expanded to estimate shark population abundance at other locations, and over time, to monitor the status, population trends and protection needs of these globally distributed predators.
Previous attempts to age chimaeroids have not rigorously tested assumptions of dorsal fin spine growth dynamics. Here, novel imaging and data-analysis techniques revealed that the dorsal fin spine of the spotted ratfish Hydrolagus colliei is an unreliable structure for age estimation. Variation among individuals in the relationship between spine width and distance from the spine tip indicated that the technique of transverse sectioning may impart imprecision and bias to age estimates. The number of growth-band pairs observed by light microscopy in the inner dentine layer was not a good predictor of body size. Mineral density gradients, indicative of growth zones, were absent in the dorsal fin spine of H. colliei, decreasing the likelihood that the bands observed by light microscopy represent a record of growth with consistent periodicity. These results indicate that the hypothesis of aseasonal growth remains plausible and it should not be assumed that chimaeroid age is quantifiable by standard techniques.
The tagging of sharks using conventional tags has long been recognized as a valuable means for studying various aspects of their life history, migrations and movements, and population structure. Conventional tags are defined as those that can be identified visually without the use of special detection equipment. Tagging studies specifically targeting sharks began in the late 1920's, and today numerous cooperative shark tagging programs exist worldwide. Cooperative programs depend on the joint participation of scientists and public volunteers to accomplish research objectives. Benefits and problems of these programs are discussed using the tagging methodologies, protocols, and results of the National Marine Fisheries Service Cooperative Shark Tagging Program. An additional 63 shark tagging studies and programs of all types are reviewed. Information useful for behavioral, biological, and fishery management studies can be derived from data resulting from these studies, including species and size composition, sex ratios, spatial and temporal distribution, migrations, movement patterns, rates of travel, delineation of pupping grounds, distribution of maturity intervals, indices of relative abundance, and recognition of individuals. Specific tagging experiments can be designed to provide additional data on age and growth, homing and site fidelity, dispersal rate, residence time, movement rates, tag shedding, and population parameters (e.g. size, mortality, recruitment, exploitation, interaction rates, and stock identity). Sources of bias inherent in tagging and recapture data include mortality, variation in tagging effort and fishing pressure, non-recovery and non-reporting of tags, and tag shedding. Recent advances in tagging methodologies that complement and extend conventional tagging studies will further our knowledge on shark movements and migrations, particularly in the areas of resource utilization and management, space utilization, and population dynamics.
Growth parameter estimates were calculated for the tiger shark (Galeocerdo cuvier) by using tag and recapture data. Results were compared to published estimates based on bands in vertebrae. The von Bertalanffy parameters (sexes combined) based on tag and recapture growth data were as follows: L(∞) = 337 cm fork length, k = 0.178, and t0 = -1.12. Monthly length-frequency data for six year classes from birth to two years old for tiger sharks were used to verify the tag-recapture growth curve for this age range. The predicted age at maturity is 7 years for both sexes. Data from an ongoing in situ study with oxytetracycline were used in conjunction with length data to determine the effect of tagging and oxytetracycline injection on growth. The data suggest that tagging alone or tagging combined with oxytetracycline injection has little or no effect on the growth rate of tiger sharks up to two years of age.
A total of 591 great white sharks Carcharodon carcharias was caught between 1974 and 1988 in the gill nets which are maintained along the Natal coast to protect bathers from shark attack. The species represented 2,7 per cent of the total catch of sharks for the period 1978–1988 and the mean catch rate was 1,0 shark·km-net−1·year−1. Specimens ranged in size from 131 to 348 cm precaudal length, with a mode of 206–210 cm for females and 216–220 cm for males. None was mature, and the sex ratio was 1 male to 1,4 females. Catch rates were highest in the southernmost nets, with a smaller peak in the extreme north. Catches peaked in midwinter, those in the warmer, northern region lagging 1–2 months behind those in the cooler southern waters. The relationship between catches and water clarity and temperature was tenuous. Elasmobranchs were the most important prey item, occurring in 41,1 per cent of stomachs containing food, followed by teleosts at 34,7 per cent and marine mammals at 29,0 per cent, although marine mammals, mainly cetaceans, were the most common prey category in sharks longer than 250 cm. Pelagic prey items were more common than demersal species and there was evidence of sharks scavenging on animals from each of the main prey groups.
The great hammerhead shark, Sphyrna mokarran, is a cosmopolitan species that is caught in a variety of fisheries throughout much of its range. The apparent decline of great hammerhead shark populations has reinforced the need for accurate biological data to enhance fishery management plans. To this end, age and growth estimates for the great hammerhead were determined from sharks (n = 216) ranging in size from 54- to 315-cm fork length (FL), captured in the Gulf of Mexico and north-western Atlantic Ocean. Growth curves were fitted using multiple models and evaluated using Akaike's information criterion. The von Bertalanffy growth model was the best fitting model, with resulting growth parameters of L(infinity) = 264.2-cm FL, k = 0.16 year(-1), t(0) = -1.99 year for males, and L(infinity) = 307.8-cm FL, k = 0.11 year(-1), t(0) = -2.86 year for females. Annual band pair deposition was confirmed through marginal-increment analysis and a concurrent bomb radiocarbon validation study. Great hammerheads have one of the oldest reported ages for any elasmobranch (44 years) but grow at relatively similar rates (on the basis of von Bertalanffy k value) to other large hammerhead species from this region. The present study is the first to provide vertebral ages for great hammerheads.