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The condition of fish escaping from fishing gears — A review
Abstract
The capture of immature fish in many commercial fisheries is controlled by restricting the use of fishing gears or elements of fishing gears that prevent the escape of immature fish. Improving the selective characteristics of fishing gear is based on the assumption that fish escaping are not seriously damaged and able to make a complete recovery. If fish escape and die as a direct result of stress and injuries or indirectly due to disease and predation associated with gear damage, then increasing the opportunity for escape by improving selectivity may result in an increased level of unaccounted fishing mortality. This paper identifies the main fishing gear types used for harvesting marine and freshwater fish, a range of injuries, stress reactions and mortalities that can occur during capture and escape. It is concluded that immediate and delayed mortalities can occur in fish escaping from fishing gears and that the high variation in mortality rates within experiments is associated with a lack of information on how fish condition is affected by various fishing stressors and the type and severity of physical damage received. Improving selectivity without reducing damage or stress incurred during capture and escape may not be the most appropriate way of protecting immature fish.
... They demonstrated that fish stress associated with such capture is, of course, related to tow duration, but also to crowding and exposure to air [80][81][82]. However, the patterns of variation in the vitality rates that resulted in the present work have been described similarly in several discard species, including elasmobranchs, in response to capture by trawl or different gear [83][84][85]. ...
... Differently, large variations in water pressure [77,[83][84][85] and temperature [93][94][95] are already known to induce dramatic physiological stress in elasmobranchs and bony fish. These two factors can even interact to favor embolic phenomenon that can resolve with the death of individuals during capture [96]. ...
... On the other hand, coastal species exhibited a higher and lower number of active and inactive individuals, respectively (i.e., a better vitality condition with respect to deepwater species). In fact, the probability of embolic phenomenon and the temperature variation is strongly reduced with decreasing fishing depth [77,[83][84][85][93][94][95]. Furthermore, the effect of potentially harmful species in the catch mass (sea urchins, octopuses, and crabs) is buffered by the more robust skin of coastal species compared to deep water species [100,101], as a robust skin lowers AVM in elasmobranchs [98][99][100]. ...
Elasmobranchs are priority species for conservation due to their rapid decline determined by the unbalanced struggle between a fragile bio-ecology and strong anthropogenic impacts, such as bycatch from professional fishing. In this context, measuring species resistance to catch of poorly selective gear is of paramount importance. During June–October 2022, five experimental fishing campaigns were carried out in the Asinara Gulf (northern Sardinia) through 35 geographically and bathymetrically representative hauls of an area between 30 and 600 m in depth. Skates prevailed over sharks in the number of species, with seven and five species, respectively. We first evaluated the status of each individual with respect to stress due to the trawl’s catch using a three-graded scale. We also recorded individual biometrics (total and disk length, weight and sex, and maturity for males) on board by implementing the best practices in manipulating individuals for physiological recovery and release at sea. After capture, skates resulted in generally better conditions than sharks, although deepwater species of both groups exhibited a worse state than coastal species. The estimated vitality rates also depended on the size of the individuals. This work provides standardized data on the intermingled effect of size, species type, and inhabited depth on the resistance response of some elasmobranch species against capture by trawl fishery activities.
... Intense angling effort can cause a direct decline in fish populations through harvest (Hartley and Moring 1995;Post et al. 2002;Edwards et al. 2004;Lewin et al. 2006;Arlinghaus et al. 2016;Sheaves et al. 2016) and an indirect decline through discard mortality (Cowx 1998;Post et al. 2002;Cambray 2003;Coleman et al. 2004;Cowx 2004, 2006;Lewin et al. 2006;Danylchuk et al. 2011;Strehlow et al. 2012;Arlinghaus et al. 2016). In addition to the lethal effects of angling, fish captured and released by anglers are often subjected to sublethal stressors (a negative factor impacting an organisms' health) that alter physiology, which have the potential to alter fish behavior and ultimately reproductive fitness (Barton & Iwama 1991;Chopin and Arimoto 1995;Wendelaar Bonga 1997;Chrousos 1998;Cooke et al 2002aCooke et al , 2002bRapp 2009). Increased amounts of hooking, fighting, and handling leads to increased stress on fish, which ultimately compromises potential immune system responses, allowing the fish to become more susceptible to infestation by diseases and parasites (Landsberg et al. 1998;Khan 1999;Lafferty and Kuris 1999;Hoffman 1999;Lafferty and Kuris 2004;Marcogliese 2004;Hill 2008;Pracheil andMuzzall 2009, 2010;Bauer 2010;Wisenden et al. 2012;Chapman et al. 2015). ...
... Fourth, beyond instant release mortality, catch-and-release fishing practices, known to be one of the most physically stressful actions for fish (Booth et al. 1995;Meka and McCormick 2005), can alter behavior, physiology, and fitness in fish and entire populations (Chopin and Arimoto 1995;Brobbel et al. 1996;Cooke et al. 2002aCooke et al. , 2002bCowx 2004, 2006;Arlinghaus et al. 2007;Coggins et al. 2007;Cooke and Schramm 2007;Siepker et al. 2007;Richard et al. 2013;Johnston et al. 2015;Arlinghaus et al. 2016). Research of sublethal and physiological effects from catch-and-release events have been assessed in both laboratory-controlled settings and in field environments (Anderson 1998;Bettoli and Osborne 1998;Campbell et al. 2009;Cooke and Philipp 2004;Cooke and Schramm 2007;Siepker et al. 2007;Skomal 2007). ...
... A study by Kieffer et al. (1995) conducted on the effects of catch-and-release activities on nesting male smallmouth bass (Micropterus dolomieu) found that increased exhaustion due to increased angling duration negatively impacted reproductive success, reducing fitness. Additionally, several studies have identified post-release survival (Marnell and Hunsaker 1970;Warner 1976;Schaefer 1989;Hubbard and Miranda 1991;Bendock and Alexandersdottir 1993) and mortality rates (Muoneke and Childress 1994;Chopin and Arimoto 1995;Bartholomew and Bohnsack 2005) for various fish species. ...
I wanted to determine if catch-and-release angling increased larval trematodes in small (50-160 mm) bluegill (Lepomis macrochirus). I used angling effort as a proxy for amount of catch-and-release angling. I assumed bluegill assessed, due to their size and age, experienced catch-and-release events. I assessed larval trematode intensity, black spot (Crassiphiala bulboglossa) and white grub (Posthodiplostomum minimum centrarchi), in 750 bluegill. The first objective was to quantify the association between angling effort and reservoir area. Angling effort and reservoir area were positively correlated. The second objective was to determine if angling effort, reservoir area, bluegill age, and total length affect larval trematode intensity. I hypothesized that angling effort would positively affect larval trematode intensities, allowing larval trematode intensity to be an index of angling effort. Reservoir area, bluegill age, and total length were influential on larval trematode intensity; reservoir area and total length were negatively correlated, and bluegill age was positively correlated with larval trematode intensity, whereas angling effort was both negatively and positively correlated with larval trematode intensity. The third objective was to determine if angling effort, reservoir area, bluegill age, total length, and larval trematode intensity affect condition of bluegill. I hypothesized that increased angling effort and increased larval trematode intensity, and associated stressors from both variables, would decrease condition of fish. Reservoir area, total length, and larval trematode intensity were influential on condition factors, and angling effort and bluegill age were partially influential; reservoir area, bluegill age, and larval trematode intensity were positively correlated with three condition factors (viscerosomatic and hepatosomatic indices, and Fulton's condition factor), whereas the angling effort and total length were positively and negatively correlated with condition factors. Overall, the effects of catch-and-release angling activities provide limited support for the hypotheses I put forth, indicating that larval trematode intensity is not a viable indicator of angling effort. iv ACKNOWLEDGEMENTS
... For fish discarded from fisheries, behavioural impairment due to stress and/or a failure to recover from the stress event can have fitness effects both directly (e.g., increased probability of predation; Raby, Packer, et al., 2014;Raby, Packer, Danylchuk, & Cooke, 2014) and indirectly (e.g., impaired foraging or swimming abilities; Gregory & Wood, 1999). Extensive comparative physiology research has established that the duration and magnitude of physiological disturbance following acute stress, such as a capture event, are proportional to the severity of the stressor (Chopin & Arimoto, 1995;Cook, Hinch, Watson, et al., 2018). Therefore, the type and duration of a stressor have consequences for the severity of response exhibited by the fish and recovery time required (Kieffer, 2000). ...
... F I G U R E 2 Mitigation measures for each commercial gear type covered by this review that would be the most effective in reducing the severity of stress experienced by discarded fishes, and that could also be practically employed in many fisheries It is important to note that many factors can exacerbate the response to individual stressors. While each stressor experienced during capture may independently elicit a general stress response, there is real potential for effects to be interactive (Chopin & Arimoto, 1995;Crain, Kroeker, & Halpern, 2008), the cumulative effects of which are beyond the scope of this paper. Additionally, we have not provided an exhaustive list of all stressors potentially influencing discarded fish. ...
... (Continues) size, species), mesh type and relative mesh size also influence the degree and severity of entanglement and injury (Chopin & Arimoto, 1995 (Chopin & Arimoto, 1995;Gilman, 2011). However, reducing net constriction while holding fish for brailing is perhaps a simpler means to reduce hypoxia and crowding, and has been shown to improve fish condition . ...
Discarding non‐target fish from commercial fisheries is controversial and has been a persistent concern for fisheries managers globally. Discard management strategies typically begin by understanding mortality rates among discarded fish, a challenging task given the dynamic, highly context‐specific nature of fisheries. An alternative is to develop our knowledge of how stressors operate by first understanding the causes of mortality that drive this context dependence. Particularly relevant to mitigation efforts is an understanding of how fish respond to the physical factors of fishing, such as the gear itself and methods of fishing and handling the gear. We provide a synthesis of how commercial fishing methods may influence discard mortality and outline means by which capture‐induced stress and injury can be mitigated for common commercial gear types, emphasizing method variants or alternatives during capture, handling, and release that could improve survival. This synthesis identifies exhaustion and injury as the most detrimental and ubiquitous stressors experienced by discarded fish, with few options for mitigating their effects. Trawls and hanging net fisheries are identified as the most harmful gears for by‐catch, characterized by high stress regardless of method variants and limited options for mitigation. Irrespective of gear type and type of stressor, minimizing durations of capture and handling and encouragement of good handling behaviour (e.g., during landing and sorting) will reduce the magnitude of stress and injury in fish, and ultimately increase survival.
... The objective of studies on escape mortality is to demonstrate that a sufficient proportion of the released fish survive to justify their short-term loss from the catch. In many cases, escape occurs after the fish have been subjected to a wide variety of capture-related stressors and possible injury through contact with other fish, debris, or the fishing gear itself (reviewed by [18][19][20]). For trawled gear, the key variables affecting escape survival include tow duration, catch composition, the weight of the catch, mesh size/shape, and the codend circumference [18,[21][22][23][24]. ...
... These studies should also attempt to replicate variations in commercial fishing operations, including seasonality, fishing depth, towing duration, and associated catch sizes and compositions. Data from these studies could be used to reduce the uncertainty in stock assessment modeling associated with unaccounted mortality and its bias of fishing mortality estimates [17][18][19][20]66,67]. In the meantime, the sensitivity of stock assessment models to such escape mortality data could be assessed using simulation exercises (e.g., [17]). ...
Stock assessments routinely evaluate the status of commercially harvested species, but seldom account for the possible mortality of released or escaping fish. This study presents a method for estimating the escape survival of the red mullet (Mullus barbatus) from demersal trawling in the Central Mediterranean Sea. Fish escaping from the trawl codend were collected in a detachable cage, which was lined to reduce water flow and protect the sampled fish from further fatigue and injury. Control fish (from an open codend) showed high survival, 94% (87–97%, 95% Confidence Interval), and minimal injuries, while fish escaping through codend meshes had significantly increased injuries and reduced survival, 63% (55–70%). During 7 days of captive monitoring, treatment group mortality was highest in the first 24 h and ceased for both groups within 48 h. Conflicting length-related mortality was observed, where larger treatment fish had a higher probability of dying, while the opposite was observed in the controls. Analysis showed that treatment fish were significantly more injured than control fish, with treatment fish predominantly injured in the head zone. In conclusion, this improved methodology should be repeated to provide accurate escape mortality estimates for the improved stock assessment of the red mullet in the Central Mediterranean.
... The final question that remains unanswered pertains to the survival of pollock escaping through codend meshes. Survival of escaping pollock has not been examined, and for other species, the chance of surviving this process may be high (Soldal et al., 1993;Chopin and Arimoto, 1995) or low (Suuronen et al., 1993b;Chopin and Arimoto, 1995). If survival of pollock escapees was low, then estimates of fishing mortality may be biased if codends used in this fishery permit escapement of undersized fish. ...
... The final question that remains unanswered pertains to the survival of pollock escaping through codend meshes. Survival of escaping pollock has not been examined, and for other species, the chance of surviving this process may be high (Soldal et al., 1993;Chopin and Arimoto, 1995) or low (Suuronen et al., 1993b;Chopin and Arimoto, 1995). If survival of pollock escapees was low, then estimates of fishing mortality may be biased if codends used in this fishery permit escapement of undersized fish. ...
The effectiveness of codend meshes in permitting the escapement of undersized walleye pollock (Theragra chalcogramma) in the Bering Sea pelagic trawl fishery was tested during 13 July–1 August 1994. The alternate-haul method was used to compare catches made with treatment codends (i.e. large mesh codends) and a standard codend (i.e. small mesh codend). Four catcher vessels towed test codends that were fitted directly to their trawl gear. Codends were detachable, and catches were delivered to a factory trawler where sampling took place. Catch weights using treatment codends ranged from 0.3 to 79 t. Escapement of undersized pollock (less than 36cm) decreased as catch size increased for all treatment codends, until the retention of small pollock in the treatment codends was not significantly different from that in the standard codend (i.e. when catches of treatment codends exceeded 40 t). Potential benefits of codend mesh size regulations for this large-volume fishery are therefore debatable unless catch sizes are somehow restricted.
... The main sources of such mortality include pre-catch losses and discards mortality. However, losses may also occur from ghost fishing mortality and other combined effects of interacting sources of stress and injury from fishing operations (Chopin and Arimoto, 1995;Gilman et al., 2013). All these components of mortality have one thing in common: they are generally not easily quantifiable during fishing operations, but instead must be estimated through elaborative research. ...
... PRE-CATCH MORTALITY Pre-catch losses occur when organisms are caught, or collide with the vessel or gear, and die but are not brought on board when the gear is retrieved (Chopin and Arimoto, 1995;Broadhurst et al., 2006;Gilman et al., 2013). For example, fish may die and fall from the gear before retrieval, or crew may intentionally release a portion of or the entire catch prior to landing on board, often referred to as 'slipped' catch (Box 1). ...
A Third Assessment of Global Marine Fisheries Discards
... The review by Kennelly and Broadhurst 16 highlighted that sorting grids can improve the post-selection survival of juveniles compared to the codend meshes (especially diamond meshes), which tend to close during trawling. In several studies, grid-escaping fish were in fact observed to have minimal injury and stress [65][66][67] . Among Mediterranean selectivity studies, information on the vitality rates of the specimens escaping from selectivity devices is currently scarce, and absent in studies on JSG 27 . ...
Sorting grids to exclude the juveniles of species targeted by bottom trawl fisheries from the catch are among the most promising solutions to reduce discards. We tested a two-sections Juveniles’ Sorting Grid (JSG) in a Mediterranean fisheries restricted area. First, we provided information on the vitality of individuals escaping from the JSG bars during towing, by analysing underwater footage. Then, we evaluated the catch performance of the JSG-equipped trawl compared to a standard trawl by analysing both the full species community in the catches and the main commercial species. The probability for individuals to be alive while escaping from JSG was always higher than 65% (on average), with some species (e.g. red mullet, gurnards, 91–99% on average) showing significantly higher probability than others (e.g. European hake, crustaceans, 65–82% on average). The installation of a JSG in the trawl net did not change the overall catch composition in the codend, although significant differences were observed at the single species level. The JSG was effective at reducing undersized individuals of European hake, although a loss of legal-sized individuals was observed due to escapement. A significantly lower retention of the JSG-equipped trawl was also observed for other commercial species, such as deep-water rose shrimp and broadtail shortfin squid.
... This method allows for rapid attainment of specific depths, often within minutes, facilitating the retrieval of fish, typically accomplished within a five-minute timeframe per catch. In contrast, trawling necessitates the use of larger nets, resulting in a prolonged process of 15 to 30 min to reach desired depths, followed by several hours of trawling at speeds ranging between 2-4 knots and additional time required for retrieval 40,43 . It has previously been documented that many hormonal and ionic stress-related blood parameters remain within resting levels if blood samples are obtained quickly enough after capture 44 . ...
The effects of pelagic trawling on the health and welfare of Atlantic herring (Clupea harengus L.) were investigated on a refrigerated seawater vessel operating in the North Sea. A total of 495 Atlantic herring (Clupea harengus L.) were sampled during five hauls from two fishing trips in September 2021 and 2022. For assessments of consciousness and mortality, a Reflex Action Mortality Predictor test (i.e. RAMP-test) was used on herring collected following trawling and pumping. Inspections for external and internal damage or wounds were performed via morphological welfare indicators and analyses of photos and radiographs. In addition, blood samples were taken and analysed for haematological indicators of stress. Following trawling and pumping, only 5% of the investigated herring showed signs of external wounds associated with the morphological indicators of welfare, and no internal damage was observed in the radiographic inspections. However, 96% of the assessed herring scored 0 on all three reflexes included in the RAMP-test and were therefore judged dead. On average, herring lost 95% of their scales, while 95% of herring had a very high degree of ruptured red blood cells (i.e. haemolysis). Extensive scale loss results in a deterioration of the skin's protective barrier function, which in turn impairs the osmoregulatory capacity of the herring. This was evident by elevated levels of plasma osmolality and circulating chloride concentrations, which could also likely explain the high occurrence of haemolysis in captured herring. Extended trawling time and larger catch size proved to be two important factors to consider, as the former led to increased plasma levels of osmolality, whereas the latter was associated with elevated plasma levels of lactate and cortisol. In conclusion, the high mortality appears to be influenced by a combination of factors such as severe stress, loss of osmoregulatory ability, crowding density within the trawl, and extended trawling times. This study provides important information on the welfare of wild Atlantic herring caught using pelagic trawls and highlights areas where improvements can be made to safeguard the welfare of fish captured in pelagic fisheries in the future.
... As many as 30 billion individual fish may be captured and released annually by recreational fisheries alone (globally; Cooke and Cowx, 2006) with a larger but generally unknown number captured in commercial fisheries (Alverson et al., 1994). Many released fish ultimately survive and reproduce, but that is not the case for all fish or fisheries interactions (Chopin and Arimoto, 1995;Campbell et al., 2010a;Raby et al., 2011;Wilson et al., 2014). Animals that are released (without tracking devices) have unknown fate, and fisheries therefore rely on scientific validation of mortality predictors that can improve fishing practices and guide management approaches. ...
Estimating the survival probability of animals released from fisheries can improve the overall understanding of animal biology with implications for fisheries management, conservation and animal welfare. Vitality indicators are simple visual measures of animal condition that change in response to stressors (like fisheries capture) and can be assessed to predict post-release survival. These indicators typically include immediate reflex responses which are typically combined into a score. Vitality indicators are straight-forward and non-invasive metrics that allow users to quantify how close (or far) an animal is from a normal, ‘healthy’ or baseline state, which in turn can be correlated with outcomes such as survival probability, given appropriate calibration. The literature on using vitality indicators to predict post-release survival of animals has grown rapidly over the past decade. We identified 136 papers that used vitality indicators in a fisheries context. These studies were primarily focused on marine and freshwater fishes, with a few examples using herptiles and crustaceans. The types of vitality indicators are diverse and sometimes taxa-specific (e.g. pinching leg of turtles, spraying water at nictitating membrane of sharks) with the most commonly used indicators being those that assess escape response or righting response given the vulnerability of animals when those reflexes are impaired. By presenting Pacific salmon fisheries as a case study, we propose a framework for using vitality indicators to predict survival across taxa and fisheries.
... Estimating the survivability of fish discards and escapees has been a key component when quantifying and mitigating sources of unaccounted fishing mortality (e.g. Chopin and Arimoto, 1995;Davis, 2002;Gilman et al., 2013). Demonstrating post-capture survival in Europe has become more important since the introduction of the landing obligation (LO) in 2011 (Rihan et al., 2019). ...
... Fish caught in traps are subject to stress and injuries from handling (Cook et al., 2018), air exposure (Cook et al., 2015), attempts to escape (Luckhurst and Ward, 1987;Renchen et al., 2012), and barotrauma (Bohnsack et al., 1989;Gale et al., 2011). Postescape or postrelease sublethal effects of these stressors can include disease, slowed growth, and impaired reproduction (Chopin and Arimoto, 1995;Gale et al., 2011). Reducing fish bycatch in the first place limits such stressors and reduces the likelihood of immediate or delayed mortality that might otherwise result. ...
... This was advantageous because other capture methods are selective (e.g. size selective) to some degree (Rudstam et al., 1984;Chopin and Arimoto, 1995). Similarly, sharks might actively avoid SCUBA divers (Bradley et al., 2017c), which could bias catch probability [reviewed in (Latour, 2004)]. ...
The assessment of parameters population size and individual home range is important for effective conservation management of sharks. This study uses the novel application of photo identification (photo-ID) to BRUVS footage as a non-invasive alternative to tagging in order to generate individual capture histories. These were used in mark-recapture models to estimate effective population sizes and to determine home ranges. In the Cayman Islands a total of 499 shark sightings of six coastal shark species were recorded on BRUVS from 2015 - 2018, but re-sighting rates were only sufficient for the determination of population parameters for two species - Caribbean reef shark (Carcharhinus perezi) and nurse shark (Ginglymostoma cirratum). The calculated super-population sizes for Caribbean reef shark (180 ± 37 SE) and nurse shark (336 ± 61 SE) were greater than the estimates for each species based on a closed-population model (Caribbean reef shark: 128 ± 40 SE, nurse shark: 249 ± 48 SE), though both measures indicated that there were about twice as many nurse sharks (1.3 - 1.8 sharks/km²) as Caribbean reef sharks (0.7 – 1 shark/km²) within the study area. The demographic compositions included numerous immature individuals, indicating that breeding of both species takes place within the study area of 188 km². Most recognizable individuals of both species showed linear home ranges of <20 km, but a few individuals were observed to have moved longer distances (Caribbean reef shark: 125.37 km, nurse shark: 156.07 km). The data indicate that the home ranges and long-distance movements of individual sharks observed within the islands’ marine protected areas (MPAs) often extend to areas beyond the MPA’s boundary, potentially exposing them to fishing activities. This study provides the first estimates of population size for Caribbean reef and nurse sharks in the Cayman Islands and the first estimate of a Caribbean reef shark population globally.
... Understanding the impacts of commercial fisheries on the biological diversity of the ecosystem is complex. As part of the catch, nontarget catch, or bycatch, can be retained for personal use, for sale, or returned to the water, as defined by the fishing regulations (Chopin and Arimoto 1995;Hall et al. 2000;Davies et al. 2009;Gavaris et al. 2010;Pezzack et al. 2014). Bycatch can also be characterized by the nature of the interaction with the fishery such as vessel and fishing gear in-teractions with marine mammals (Read et al. 2006). ...
The impact of the southern Gulf of St. Lawrence American lobster (Homarus americanus) fishery on species bycatch is currently unknown. The composition of the incidental catch, both nonharvestable lobster (by fisheries regulations) and nonlobster species, was systematically collected over the 2015 spring and summer fishing seasons. A total of 51 948 (7147 were nonlobster taxa) individual organisms weighing 13 987.60 kg (1223.91 kg of nonlobster taxa) were captured as bycatch during 73 fishing trips. By weight per trip, the most common lobster bycatch were undersized male and females, and the highest nonlobster species catch were Atlantic rock crab (Cancer irroratus). A semiquantitative assessment of injury and vitality was applied to bycatch as a proxy for discard mortality. The majority of the individuals assessed for visible injury were deemed uninjured (98% both fish and invertebrates); however, postrelease mortality was not measured. A smaller study in 2019 corroborated the 2015 catches and supported current assumptions that the passive gear type, the low diversity of bycatch, and the rapid hand-sorting of the trap minimize the impact of the lobster fishery on incidentally captured taxa. Further scientific monitoring is recommended to better account for all sources of mortality in stock assessments and rebuilding plans.
... For example, compared to conventional codends made from 30-mm diamond-shaped mesh, designs constructed entirely of square-shaped mesh (between 20 to 30 mm hung on the bar) have reduced the bycatches of small fishes from some of NSW's estuarine seines and stow nets by up to 95% (Macbeth et al. 2005a,b,c). Assuming the majority of organisms escaping from such designs actually survive the process (Broadhurst et al.1997), their wide scale introduction should positively benefit stocks of these species (Chopin and Arimoto 1995). ...
The catches and bycatches from stow and trap nets and seines used by commercial fishers in Lake Illawarra, southeastern Australia, were assessed via an observer-based sampling program during the 1999/2000 fishing season. Observed retained catches included Penaeus plebejus, Metapenaeus macleayi and M. bennettae, while bycatches comprised a total of 48 species of teleosts and 9 species of invertebrate. Average daily catches and bycatches were greatest in stow nets and least in trap nets. Bycatch composition varied greatly among gear types and for trap nets, between the 1st and 2nd half of the fishing season. Gerres subfasciatus, Acanthopagrus australis, Portunus pelagicus and Sillago maculata were numerically most abundant in seines, Centropogon australis, Pomatomus saltatrix and Loligo sp. in stow nets and G. subfasciatus, Loligo sp., Hyporhamphus regularis and C. australis in trap nets. Trap and stow nets accounted for greatest (80%) and least (2%) reported fishing effort, respectively. Trap nets accounted for 82% of the estimated total penaeid catch and 69% of estimated total bycatch during the fishing season. The results are discussed in terms of differences in the selection mechanisms and spatial and temporal operations of the 3 gears and consequences for sustainable and environmentally-responsible fishing.
... Although it is common to think of fishing in terms of fish that are captured and released, fish can also interact with fishing gear and escape without being landed. For example, a fish could escape from a commercial gill net or break the line when being reeled in by an angler (Chopin and Arimoto, 1995). These interactions can lead to sublethal impacts and collateral mortality but are just beginning to be explored in many fisheries (Falco et al., 2022), including interactions with various environmental factors. ...
Marine and freshwater fisheries are more important than ever for sustaining human populations but are also facing unprecedented threats from the combined effects of multiple environmental stressors. Here we review how the rapidly changing abiotic environment of fish may affect interactions between fish and fishers, at both the individual and population levels. Throughout, we highlight the role of physiological mechanisms underlying the sensitivity of fish to multiple stressors and their interactions with fishing gears. For each step in a typical capture sequence, we discuss how stressors can alter the behavioral and physiological mechanisms of capture and potential recovery after release or escape. We also consider possible feedbacks among fishing practices, environmental stressors, and physiological response of fish, including the potential for harvest-associated selection and evolutionary effects. Fisheries can also induce changes to the biotic environment, including changes in population density, species interactions, and prey density, which can in turn alter the physiology of individual fish, entire ecosystems, and the fisheries themselves. We conclude by highlighting priority research areas required to advance our understanding of the effects of multiple stressors on fish physiology and behavior within the context of global fisheries.
... For large fish, this may be irrelevant as they are retained and processed on board, but for small specimens, internal injuries may compromise survival due to a reduced chance for escaping, or increased risk for predation (e.g. Broadhurst et al., 2006;Chopin and Arimoto, 1995;Gilman et al., 2013;Kaiser and Spencer, 1995;Raby et al., 2014;Ryer, 2004). Increased fishing mortality may lead to disturbed food web structures and population dynamics of other species Hiddink et al., 2011;Kaiser et al., 2002;van Denderen et al., 2013). ...
Electrical pulse fishing has been widely adopted by Dutch fishers as an economically viable alternative to tickler-chain trawling for common sole (Solea solea) in the North Sea. Concerns exist, however, that the use of electrical pulses may cause spinal injuries and haemorrhages, as previously shown for Atlantic cod (Gadus morhua). To find out whether other gadoids are similarly affected, we studied injury occurrences in whiting (Merlangius merlangus) catches on commercial vessels. To distinguish mechanically and electrically-induced injuries, we compared (1) injuries for pulse gears with electrical pulses either turned on or off and (2) injuries from pulse-trawl catches with those in tickler-chain trawling. Spinal injuries were visualised with X-radiography and internal haemorrhages with subsequent dissection. Injuries were categorised on a severity scale and their location was quantified along the anteroposterior fish axis. Major spinal injury occurrence in (1) pulses-on and pulses-off samples were lower than 1% and not significantly different between catch methods. Major spinal injury occurrence was slightly higher in (2) tickler-chain catches (2.4%) than in pulses-on samples (1.1%). Major haemorrhage occurrences were also low. The slightly higher occurrences of these haemorrhages in pulses-on samples (1.8%) compared to fish caught with tickler chains (0.3%) and their locations suggest that they may be partly related to electrical-pulse exposure. Overall, our results indicate that injuries in whiting are rare and primarily due to mechanical impact. These findings suggest that pulse trawling is unlikely to impose increased mortality on whiting populations compared to the tickler-chain technique.
... Bunların arasından doğrudan yaklaşım ise ıskarta edilen balıkları ve güvertede ölen balıkları anında gözlemlemektir. Fakat ıskarta edilen balıklarda gözlemlenemeyen ve dolayısıyla bilinmeyen ölümler mevcuttur (Chopin and Arimoto, 1995;Davis, 2002 Davranış bozukluğu önemli bir ekolojik ölçüm olmakla beraber ıskarta edilme gibi birçok stres kaynağına bağlı olabilir ve bilinmeyen ölümle ilişkilendirilebilir (Beitinger, 1990;Schreck et al., 1997;Davis and Parker 2004 ...
The mortality rate of discards is an event which needs to be studied in various aspects. For fishery management the rate and the posibility of survival for the aquatic organism already discarded is unclear. Therefore it is important that the mortality rate and behavioral disorders caused by the stres occuring both during and after the fishing operation should be well investigated.
This study aims to bring to light such disorders and the eventual mortality of Sparus aurata below legal catch rate in a simulated trawl operation. To this end, behavioral disorder of fish in the aftermath of trawling operation was tested in two different methods through observing the responds to different stimulants. In the first method of the tests all the fish in the tank was compared with the control groups. During this process, in addition to their free movement in the tank, the responses of fish to noise, to other things and to touch were counted. In the second method with the fish out of water, reflex measurement was carried out individually. The fish positioned with a spongy holder was checked for general body reflex. Furthermore, with the help of a probe, moment of mouth as well as gills and throat reflexes and sight respond were recorded. The reflexes from these two processes were taken as the extent of behavioral disorder and a relation with delayed mortality was established.
According to the data, a considerable number of fatalities among those returning to the water come about within approximately 24 hours and such mortality is called delayed mortality. There is a proportional connection between behavioral disorder and delayed mortality. On the other hand, however high the behavioral disorder might be, the mortality rate remains at a certain proportion. A considerable number of fish survived under confined medium in the laboratuary tanks.
... The exact stressors and degree of stress (e.g. exhaustion, barotrauma, physical injury, hypoxia stress) that fish encounter will depend on the target species (Chopin and Arimoto, 1995;Davis, 2005;Suuronen, 2005;Broadhurst et al., 2006;Benoìt et al., 2012), their body size (Hall and Mainprize, 2005;Halliday and Pinhorn, 2002), their interaction with the fishing gear (Cook et al., 2013(Cook et al., , 2019, the fishing procedures and gears used, (Cook et al., 2019;Methling et al., 2017;Wilson et al., 2014) and the environmental conditions (e.g. temperature, dissolved oxygen) present before, during and after capture and throughout the recovery period following escape or discard. ...
Recent European Union (EU) regulations have been introduced to discourage the capture of undersized specimens with the
aim of reducing the bycatch mortality imposed by commercial fisheries. We argue that we still lack accurate data regarding
basic information required to properly implement these regulations for most Mediterranean ecosystems, including the true
mortality imposed by fisheries, escape rates from fishing gears and the capability of specimens to survive following discard.
We suggest that additional reliance on physiological biomarkers could assist in all aspects of the data collection required to
support implementation of the EU discard ban (aka landing obligation), particularly in determining which species should
receive special dispensation from this policy. Ideally, this new approach, here termed the ‘Fisheries Environmental and
Physiological Stress Analysis’ (FEPSA), would become an important step for any fish stock assessment within the ecosystem
approach to fisheries management and the recognition of Good Environmental Status, as established by the EU in the Marine
Strategy Framework Directive (2008/56/EC). In particular, the main goal of FEPSAwould be applying the study of physiological
stressors to exploited stocks to estimate the so-called collateral fishing mortality, which includes the mortality experienced by
fish that escape after interacting with fishing gears or that are discarded, with some degree of injury or physiological stress.
The approach outlined here, which is described for bottomtrawls but adaptable to any other type of fishing gear, is not a trivial
undertaking but is a requirement for collecting the data requiredby recentEUfisheries policies.Whilewe agree that the threats
to marine biodiversity posed by fishing and associated discard practices require strong policy interventions, we emphasize
that the research programsneeded to support such initiatives, including the landing obligation, should be given equal priority.
This is particularly true forMediterranean fisheries, which are at a complex intersection of jurisdictional boundaries, numerous
additional ecosystemthreats including widespread pollution, therma
... The whole catch or a large proportion of it is usually lost. et al., 1983;Chopin and Arimoto, 1995;Suuronen, 1995;Broadhurst et al., 2006;FAO, 2020). The discard rates reported by the FAO do not account for pre-catch losses, which are likely more relevant than discards in pelagic fisheries (Pérez Roda et al., 2019). ...
Unaccounted mortality caused by discarding or pre-catch losses is a major challenge for fisheries management. In pelagic fisheries, a considerable proportion of catches may be lost due to intentional release of unwanted catch (slipping) or net bursts (fishing net tears due to the weight of the catch). Here we review and estimate ranges of discard and pre-catch mortality for two important pelagic fisheries, the Northeast Atlantic (NEA) mackerel and Norwegian spring spawning (NSS) herring, and explore the effects on stock estimates and catch advice. We show that mortality caused by discarding, slipping, and net bursts is unknown but probably corresponds to a considerable percentage of total registered catches. Including estimated unaccounted mortality into assessment models leads to underestimation of the stock levels by 3.7–19.5% and 2.8–6.8% for NEA mackerel and NSS herring, respectively, corresponding to up to several million tonnes of fish that die annually due to fishing without being landed. If discard and pre-catch mortality were eliminated, allowed catches could increase by 10–20%. We demonstrate that unaccounted mortality in pelagic fisheries may be substantial, affecting stock estimates and catch advice. This may undermine the sustainable management and efficient use of pelagic resources.
... Typically, aquatic net sampling methods, such as trawling and gill netting, have been used to assess the SS of fish communities, but these methods induce high mortality of fish and are labor-and cost-intensive [1,18]. Furthermore, net sampling is inherently size-selective and may therefore introduce bias in SS analyses [19][20][21]. ...
Net sampling by trawling and hydroacoustics was used to methodologically compare size spectra (SS) of the pelagic fish community in a deep lake across 12 years of sampling. Hydroacoustic SS were generated based on either single-echo detections (SEDs) or tracked-echo groups (TEGs) from 20 cross-lake transects. Trawl SS were obtained by a midwater trawl in four pelagic depth layers. All SS were derived from maximum likelihood estimations of exponent b of a continuous fish body mass distribution. The arithmetic mean exponent b was similar for all methods, and there were no significant differences of b among the three methods across years. However, visual inspection indicated that the SS differed considerably between trawling and hydroacoustics in some of the years, primarily when high densities of 0+ coregonid fishes were strongly spatially aggregated and hence caught by the trawl. Accordingly, there was no correlation between SS generated by trawling and hydroacoustics. In contrast, SS generated by SEDs and TEGs were significantly correlated, indicating reliability and reproducibility of obtaining SS by hydroacoustics. The SS estimated by TEGs revealed a positive trend of exponent b over the years since 2005, potentially reflecting the recent eutrophication of Lake Stechlin, which may lead to higher fish growth rates. We conclude that hydroacoustics may help to generate more precise SS of the pelagic fish community in our study lake than midwater trawling. However, the truthfulness of SS estimates cannot be evaluated because of the inherent difficulty in determining the true densities and sizes of fishes in lakes.
... Many fishing gears capture fish of a certain size range due to the selective characteristics of the fishing gear used (Millar, 1992). Therefore, it is critically important to know the fish sizes that are vulnerable to capture to improve resource management (Chopin & Arimoto, 1995). Consequently, the variability in size has important implications for diverse aspects of fisheries science and population dynamics (Erzini, 1994). ...
This study reports length-weight (LWRs) and length-length (LLRs) relationships for three small tuna species, Scombridae: Bullet tuna [BLT], Auxis rochei (Risso, 1810); Atlantic bonito [BON], Sarda sarda (Bloch, 1793); and Little tunny [LTA], Euthynnus alletteratus (Rafinesque, 1810) from Portuguese waters. Specimens were captured by tuna trap, trawl nets and gill nets. A total of 1035 individuals were sampled and the sex was identified in 662. This study provides the first LLRs using the curved fork length (CFL) for these three species and the first LWRs using the eviscerated weight (We) for Bullet tuna. Additionally, in relation to the available information on sexed LWRs and LLRs in FishBase, this study is a first report for Bullet tuna and Little tunny and a first report for Atlantic bonito in the Atlantic Ocean. This work also improves data available for the north-eastern Atlantic and Portuguese waters for these three species.
... These findings contribute new data on the efficacy of artificial illumination to reduce Pacific halibut bycatch, but also their ability to reduce their bycatch before trawl capture. Capture-escape processes can lead to unobserved and unaccounted post-release mortality caused from physiological stress, fatigue, and injuries (Chopin and Arimoto, 1995;Davis andOlla, 2001, 2002;Ryer, 2004;Davis, 2005). Reducing Pacific halibut bycatch before trawl capture would likely have a positive effect on lowering this mortality. ...
In the U.S. West Coast groundfish bottom trawl fishery, Pacific halibut (Hippoglossus stenolepis) bycatch can impact some fishers' ability to fully utilize their quota shares of groundfishes. In this study, we compared the catch efficiency for Pacific halibut and four commercially important groundfish species between an illuminated and non-illuminated trawl. The illuminated trawl caught significantly fewer Pacific halibut and sablefish than the non-illuminated trawl. For Dover sole (Microstomus pacificus), petrale sole (Eopsetta jordani), and lingcod (Ophiodon elongatus), the illuminated trawl caught fewer individuals than the non-illuminated trawl. However, this catch difference was not statistically significant. Physiological data collected on Pacific halibut caught in illuminated and non-illuminated trawls show blood levels of cortisol, a stress hormone, were significantly higher in fish caught in the illuminated trawl than in the non-illuminated trawl in the absence of differences in condition factor or fat content. While our results have obvious implications for the West Coast groundfish bottom trawl fishery, our findings could also have potential applications in Alaska and British Columbia, Canada trawl fisheries where Pacific halibut bycatch occurs.
... These findings contribute new data on the efficacy of artificial illumination to reduce Pacific halibut bycatch, but also their ability to reduce their bycatch before trawl capture. Capture-escape processes can lead to unobserved and unaccounted post-release mortality caused from physiological stress, fatigue, and injuries (Chopin and Arimoto, 1995Davis and Olla, 2001Ryer, 2004Davis, 2005. Reducing Pacific halibut bycatch before trawl capture would likely have a positive effect on lowering this mortality. ...
In the U.S. West Coast groundfish bottom trawl fishery, Pacific halibut (Hippoglossus stenolepis) bycatch can impact some fishers' ability to fully utilize their quota shares of groundfishes. In this study, we compared the catch efficiency for Pacific halibut and four commercially important groundfish species between an illuminated and non-illuminated trawl. The illuminated trawl caught significantly fewer Pacific halibut and sablefish than the non-illuminated trawl. For Dover sole (Microstomus pacificus), petrale sole (Eopsetta jordani), and lingcod (Ophiodon elongatus), the illuminated trawl caught fewer individuals than the non-illuminated trawl. However, this catch difference was not statistically significant. Physiological data collected on Pacific halibut caught in illuminated and non-illuminated trawls show blood levels of cortisol, a stress hormone, were significantly higher in fish caught in the illuminated trawl than in the non-illuminated trawl in the absence of differences in condition factor or fat content. While our results have obvious implications for the West Coast groundfish bottom trawl fishery, our findings could also have potential applications in Alaska and British Columbia, Canada trawl fisheries where Pacific halibut bycatch occurs.
... Humborstad et al. 2009Humborstad et al. , 2016aMidling et al. 2012;Misimi et al. 2014;Olsen et al. 2013), several of which utilise and refer to studies that could have an associative or indirect impact upon the welfare of captured fish. A comprehensive collection of publications and reviews deals with the mortality of escapees and discards from commercial fishing gears (Broadhurst et al. 2006;Chopin and Arimoto 1995;Suuronen 2005;Suuronen and Erickson 2010). Many of these (e.g. ...
Capture-based aquaculture (CBA) combines aquaculture practices with capture fisheries to keep the catch alive for either short or long periods of time, for feeding or for live storage. CBA enables us to market numerous species ranging from molluscs, scallops and crustaceans to fish such as tuna, cod, eel and groupers. In CBA, handling and adaptation to new environments have an additional influence upon the stressors to which fish are exposed during capture, and the duration of this impact increases dramatically from minutes and hours in traditional fishing to days and months in CBA. We show how a strong focus on welfare is already present in cod CBA fisheries and the rationale behind this focus. We present a case study on CBA of Atlantic cod (Gadus morhua) as a robust example and model species for detecting welfare risks and mitigating against them. We discuss the main welfare issues in relation to the three broad phases of capture, transport and live storage, and identify common current fish welfare challenges in CBA. We highlight the advantages of pursuing this approach using lessons learnt from an industry in which fisheries and aquaculture meet and where an existing and successful knowledge transfer process between fisheries and aquaculture is already under way.
... Thus, in fishery management, the possible side effects of sex selection on reproductive success of the population should be considered (Zhou et al., 2010). Actually, overfishing causes damage and stress to crayfish, which negatively affected their growth and survival (Chopin & Arimoto, 1995). Even though some crayfish escape from fishing, they may be injured and die later due to physical damage. ...
Aquaculture has developed rapidly in recent years and has become one of the primary contributors to food supply worldwide. However, the immense fishing pressure on wild and commercial-farmed populations has caused population depletion. Furthermore, limited juvenile crayfish production for aquaculture and suboptimal feeding strategies (such as high inputs of artificial diets) has hindered the development of sustainable aquaculture industry. Improving fisheries management is now necessary, based on a better scientific knowledge of population dynamics, reproductive ecology, and optimal feeding strategies, in particular by determining optimal environmental parameters for reproduction and refining artificial diets inputs. In this thesis, we focused on three main questions. First (1) what is the population and reproduction dynamics of adult crayfish living in commercial ponds and how should we adjust the aquaculture management? Second (2) what are the optimal temperatures for artificial reproduction and embryonic development? And third (3) what are the optimal levels of feeding and protein composition of artificial food for crayfish growth? For the first question (1), we studied the population dynamics and reproductive pattern of red swamp crayfish (Procambarus clarkii) by estimating growth, mortality rates, and exploitation rate of a commercial population, as well their reproductive parameters (GSI, HSI, ovarian development, and fecundity). Results showed that spawning activities took place from September to November, with a mean fecundity of 429 ± 9 eggs per female, and two recruitments yearly. There were five growth cohorts and male P. clarkii were overexploited. We thus suggest reducing fishing intensity on immature crayfish and avoid sex selection during the reproductive period to improve the overall sustainability of commercial P. clarkii populations. For the second question (2), we experimentally tested the effects of water temperature to improve reproductive outputs and embryonic development. Results showed that manipulating water temperature was an effective way to induce spawning in females and optimize embryonic development to improve juvenile production, with optimal temperatures of 21 - 25°C and 25°C, respectively. We also built a temperature-dependent developmental model for P. clarkii, D (developmental time, days) = 3140837(T-2.03)-3.76. Finally, for the third question (3), we experimentally tested the effects of five different feeding levels and reduced dietary protein levels (2 experiments) on growth performance and muscle composition of juvenile P. clarkii with natural food Hydrilla verticillata. Results showed that reducing the amounts of an artificial diet to 60% satiation and/or reducing the dietary protein level of the artificial diet to a level of 26% did not significantly affect the growth performance and muscle composition of P. clarkii. Stable isotope analysis suggested that crayfish switched diets to easily available H. verticillata when feeding levels or dietary protein levels decreased. This thesis thus explored new alternatives to traditional crayfish aquaculture by adjusting fishing effort and season, manipulating crayfish culture temperature, and refining feeding strategies to reduce production costs while improving the productivity and sustainability of crayfish aquaculture.
... However, the incidence of heartbeats is an indicator of pressure or stress, which increases with the struggle to avoid the gear, hence the need for longer recovery time from fatigue. Cophin & Arimoto (1995) reported on the propensity to use the fish swimming in the trawl tip as samples for trials, as this possibly increases the likelihood of death due to stress experienced in the fishing process, despite the tendency of an escape. This study established a relationship between the amount of pressure exerted on fish during trials, including swimming speeds above 3 BL/s, and the sustained increase in heart rate. ...
The purpose of the study was to observe the heart rate of Japanese jack mackerel (Trachurus japonicus Temminck & Schlegel, 1844) and the swimming speed level during the simulation of the capture process in a flume tank. This was monitored on 11 samples of 19.1 ± 0.6 cm body length (BL) (mean ± S.D., n=11), during swimming experiments in the flume tank at 24ºC. The observations were conducted at speeds ranging from 1.3 BL/s to 5.9 BL/s, where a gradual increase was applied for each consecutive test session of 10 minutes (step-up protocol). In addition, electrocardiograph (ECG) monitoring was performed to analyze changes in heart rate at each speed level by implanting a pair of electrodes in the pericardial cavity, through the ventral side of the fish body and by a connector to the bio-amplifier and oscilloscope. The results showed an insignificant increase within the swimming speed range of 1.3-2.8 BL/s, from the average control heart rate of 78.5 beats/minute in still water. Meanwhile, a higher value was reported in the elevated speed range of 2.8-4.4 BL/s and the heart rate stabilizes in the speed range of 4.4-5.9 BL/s, at a heart rate of 174.8-182.5 beats/minute. The recovery times monitored through ECG measurements showed similarity in the time taken to attain the control heart rate from the peak heart rate (maximum), of 204.3 ± 81.7 minutes. The heart rate increases when the swimming speed of the fish is increased. Meanwhile, swimming endurance decreases when the swimming speed is increased. Under these conditions, fish required more than 120 minutes for recovery time.
... Beginning in the 1980s multiple studies have attempted to determine escapee mortality rates, with results that range from 0 to 100% mortality (Main and Sangster, 1990;Chopin and Arimoto, 1995;Suuronen, 2005). No escapee mortality results have been reported for Northwest Atlantic redfish, but their high vulnerability to discard mortality suggests that escapee mortality might be high (Benoît et al., 2013). ...
The Acadian redfish Sebastes fasciatus stock is one of the few healthy fished populations
in the Gulf of Maine. This stock recovered from decades of unsustainable exploitation in
the mid-20th century after imposition of codend mesh size restrictions and a long period
as a bycatch fishery. Current harvest levels are far below permitted levels, and therefore
the stock potentially offers additional opportunity for regional fishermen. However, based
on its history and unusual biology, re-establishment or expansion of the trawl fishery for
redfish should be conducted with caution. To assure future health of the stock, steps to
encourage additional landings should include consideration of a wide range of aspects,
including appropriate fishing gears, timing of seasons, processing, and marketing, as well
as population dynamics. This dissertation sought to provide several vital conservation
engineering or fishing technology inputs to a sustainable fishery with optimum yields in
a stepwise fashion, beginning with identification of bycatch issues, followed by codend
selectivity, and bycatch reduction. This approach, combined with data from other sources,
is adequate to inform careful decision making about increased exploitation of the stock.
As a first step, basic catch and bycatch data were collected by commercial fishing
vessels, every two to three months between May 2011 and January 2012. The vessels
used their own commercial groundfish trawls, but a relatively small mesh codend (114
mm or 4.5 in mesh size); catch and bycatch were documented by onboard observers.
The resulting catch consisted predominately of redfish (105,627 kg; 84.6% of all catch).
Pollock (Pollachius virens) was the main landed bycatch species (3,322 kg), with 13 other
species landed in smaller amounts. Discard rates using a modification of the Standard
Bycatch Reporting Method revealed that almost all were below 0.01 kg of bycatch per kg
of kept catch. These results indicate harvest of redfish using 114 mm diamond mesh can
occur without substantial catch of undersized redfish and other commercially important
groundfish species, although rates for very weak stocks, such as Atlantic cod Gadus
morhua could be problematic. Depth, time-of-year, or some other factors appeared to have an impact on the catch of undersized redfish but could not be isolated.
Next, codend size selectivity for redfish and pollock were investigated using an
innovative trouser trawl section to determine retention curves for three sizes of mesh
opening (114, 139 and 165 mm double 5 mm twine diamond) on a commercial fishing
vessel. Fifty-six tows were completed in March and April 2013. Robust selectivity models
for the mean L50s and selection ranges (SR), and confidence intervals, were developed for all three tested codends, incorporating both within and between haul variability: nominal 114 mm - L50: 22.3 cm (redfish) and 34.8 cm (pollock); 139 mm - L50: 29.2 cm (redfish) 45.6 cm (pollock); 165 mm - L50: 33.6 cm (redfish) and 52.4 cm (pollock). A simple relationship between the L50s for the two species was established.
These models can guide managers and fishermen on mesh size and retained sizes of
redfish and its primary bycatch. Additionally, simulation of fishing of the three tested
codends on the observed population indicated that substantial escape of redfish through
codend meshes occurs (51-96% of all redfish that enter the trawl). The observed size structure of the redfish in combined catches also indicates that inadequate numbers of larger redfish may be available to support a higher-priced market.
The final field phase investigated timing and location of codend escapes by redfish
using cameras and lights, and a dual grid system to increase escape of small redfish at depth. Escapes of redfish were observed on video to occur at all depths, but most frequently during net retrieval, exposing smaller redfish to more potential sources of mortality. Cameras recorded as many as 50% of estimated escapes. Testing of two bar spacings for a dual grid system with a 114 mm codend demonstrated the possibility of improving size selection through the use of size-sorting grids. While the 40 mm grid showed no differences in size structure of the redfish catch, the 50 mm spacing resulted in reductions of all sizes of redfish in the catch.
Population analysis modeling possible effects of depth-differentiated estimated rates
of escape mortality showed strong impacts of fish escapes on population trends in the
stock; these impacts were sensitive to the estimated rates, which were based on redfish
physiology and other factors. Additional modeling examining the impact of changing the
fishery selectivity indicated that the largest mesh size of 165 mm maximized yield per
recruit.
All fishing related results from this dissertation were combined with other sources to
illustrate tradeoffs in management decisions. A primary result is that, under the status quo, which includes options to use 139 or 165 mm codends, exploitation levels will likely not reach the target level. Also, use of larger meshes increases numbers of redfish escaping the codend and likely increases unobserved mortality, and can adversely affect the population size estimates. Recommendations include support for a monitored special access program with broad geographic and temporal scales, with a 114 mm codend permitted. In the longer term, refinement of a grid system, quantification of redfish codend escape mortality rates and reduction of bycatch of pollock and cod are recommended.
... Fishing often results in the catch getting wounded when their bodies rub against fishing nets or when they collide with each other, which may cause death. This is a common problem in the conservation of fishery resources (Chopin and Arimoto 1995) and live fish markets. We reported earlier that the mortality rates of four fish species artificially wounded by fishing nets and pumice stones significantly decreased after rearing the wounded fishes in diluted seawater (SW) with a salt concentration similar to that of fish 1 3 plasma (Midooka et al. 2017). ...
... The clear reduction in eulachon bycatch before trawl capture in trawls outfitted with LEDs translates to substantially fewer fish exposed to capture-escape processes within the trawl. These processes can cause physiological stress, fatigue, injuries (from contact with sorting grids, webbing, and (or) other fishes, etc.) and lead to unobserved and unaccounted postrelease mortality (Chopin and Arimoto 1995;Davis andOlla 2001, 2002;Ryer 2004;Davis 2005). Depending on its magnitude, a reduction in eulachon bycatch mortality could have important conservation benefits. ...
This study examined the extent that eulachon (Thaleichthys pacificus) and groundfishes escape trawl entrainment in response to artificial illumination along an ocean shrimp (Pandalus jordani) trawl fishing line. Using a double-rigged trawler, we compared the catch efficiencies for ocean shrimp, eulachon, and groundfishes between an unilluminated trawl and a trawl illuminated with five green LEDs along its fishing line. Results showed a significant reduction in the bycatch of eulachon and yellowtail rockfish (Sebastes flavidus) in the presence of illumination. As eulachon are a species listed in the Endangered Species Act, this finding provides valuable information for fishery managers implementing recovery plans and evaluating potential fishery impacts on their recovery and conservation. For other rockfishes (Sebastes spp.) and flatfishes, however, we did not see the same effect as the illuminated trawl caught similarly or significantly more fishes than did the unilluminated trawl. Prior to this research, the extent that eulachon and groundfishes escape trawl capture in response to illumination along an ocean shrimp trawl fishing line was unclear. Our study has provided results to fill that data gap.
... This can lead to discarding when resulting catches are undesirable in some way. Discarding can be detrimental to sustainable fishery management as discarded fish may die [8,9], which can introduce uncertainty into stock assessment if not properly accounted for [10][11][12]. ...
The release of unwanted fish from purse seines whilst still in the water is termed slipping and may lead to significant mortality following release. The objective of this study was to determine the fish welfare implications of a new slipping methodology in which fish are released via a discharge opening formed in the bunt end of the purse seine net. Video analyses of collective and individual level fish behaviour were undertaken in the Norwegian mackerel and herring purse seine fisheries, to quantitively describe slipping behaviour and to determine its driving factors. The majority of fish escaped the purse seine with the schooling structure intact as part of large groups towards the end of slipping process, increasing their speed following escape. However, there was also a tendency (24% of all escapes) to escape in a manner likely to impact negatively upon their welfare, with a breakdown in schooling structure and physical contact with the fishing gear and conspecifics. The tendency to express such welfare compromising behaviour was higher for mackerel than for herring, but was also influenced by the vessel releasing the fish, the amount of fish being slipped, how long the discharge opening had been open and the particular slipping event. These results provide important information for future science-based development of welfare friendly slipping practises.
... Although studies have examined the causes of both en route mortality and prespawn mortality associated with salmon escaping from fishing gear (e.g., Chopin and Arimoto 1995;Baker et al. 2014), most research efforts on gear-salmon interactions have focused on the consequences of intentional releases from fishing gear (reviewed in Cooke et al. 2012 andRaby et al. 2015). A recurring finding from these studies is that fish sustain external injuries such as skin abrasions and disruption of the mucous layer (Davis 2002). ...
Non‐retention in gillnet fisheries for Pacific salmon Oncorhynchus spp. can be relatively high and can cause a variety of impairments to non‐retained fish, which often leads to immediate or delayed mortality. We sought to improve the understanding of the association between gillnet escapement and injuries incurred by upriver‐migrating salmon by examining the relationship between gillnet fishing effort in the Fraser River, British Columbia, and the frequency and severity of gillnet injuries to migrating Sockeye Salmon Oncorhynchus nerka. Adult Sockeye Salmon were intercepted at a location approximately 335 km from the mouth of the Fraser River and were assessed for gillnet injuries. Gillnet fisheries targeting Sockeye Salmon operated throughout the first 320 km of the Fraser River mainstem starting at the mouth of the river. A generalized linear mixed model was used to identify the role of gillnet fishing effort, fork length, and sex on the probability of an individual fish sustaining a gillnet injury. Predicted probabilities of gillnet injury ranged from 12‐46% across all levels of fishing effort, suggesting that gillnet injuries were more prevalent among individuals that encountered high levels of fishing effort. However, fishing effort did not seem to influence the severity of gillnet injuries. Our results suggest that estimates of fishing effort may be useful in predicting the probability of gillnet injury to migrating fish, which could help managers estimate en route mortality and more accurately predict spawner escapement. This article is protected by copyright. All rights reserved.
... It seems reasonable to postulate that, under this context, shark survival depends on the interrelationships between anthropogenic and environmental factors, such as physiological capture stress from both handling and ambient temperature changes. Although several studies have elucidated the combined effects of water temperature and air exposure on fish survival (Chopin and Arimoto, 1995;Ross and Hokenson, 1997;Davis et al., 2001;Davis, 2002;Poisson et al., 2014), little is known about how air temperature or direct solar radiation influence the external body temperature of captured sharks and its potential consequences for post-release recovery or mortality (Cicia et al., 2012;Wosnick et al., 2018). The assessment of thermal dynamics upon air exposure permits not only a better comprehension of warm-shock associated to the transition from water to air but can also raise important points regarding the effects of the reciprocal cold-shock when returned to their natural environment. ...
Body temperature is a crucial component of thermoregulation, being strongly linked to variables such as energy flow, metabolic rates, activity patterns and resilience. With exception of lamnid sharks, elasmobranchs are classified as ectothermic, depending on ambient temperature for heat modulation. Despite often being removed from the water during fisheries interactions, the known effects of air exposure on sharks are limited to the hypoxia experienced. Comparatively little is known about the potential effects of changing ambient temperatures and solar radiation experienced by sharks during air exposure, and if such scenarios may compromise their thermal dynamics and survival. Here we used infrared thermography (IRT) to measure external body temperature of 10 different shark species (N = 62), ranging in size from 106 to 340 cm total length, experimentally exposed to air. We tested the hypothesis that all individuals would exhibit body surface temperature increases when air-exposed, with temperature uniformly distributed across the body surface regardless of species. Our results did not support this hypothesis. Although ectothermic, sharks exhibited significant species-specific variations in heat distribution and warming along the body surface. Moreover, these thermal patterns were significantly impacted by both environmental factors (water temperature at capture) as well as biological traits (shark size and body region). Multivariate analyses separated the 10-shark species into five groups according to the influences of shark body size, body region and water temperature on variations in the thermal profiles detected. We discuss the potential physiological, ecological and conservation implications of these findings.
... Wherever fisheries exist, the process of fishing can have detrimental impacts on birds, mammals, non-target fish species, and even target fish species that interact with gear but are not landed (Alverson et al., 1994;Baker and Schindler, 2009). While release or escape may provide an opportunity for survival, fish interacting with fisheries gear are likely to undergo an energy intensive and immuno-compromising stress response, receive external and internal damage, and become vulnerable to predators during or following capture (Chopin and Arimoto, 1995;Uhlmann and Broadhurst, 2015). This experience can lead to mortality immediately following the capture experience (Thompson et al., 1971), delayed mortality occurring days to weeks later (Donaldson et al., 2011), or sub-lethal effects that alter behavior (e.g. ...
Following interactions with fisheries gear, fishes may experience delayed mortality or display modified behavior. The physiological status of fish at the time of capture, including the presence of infectious agents, can also influence survival outcomes. To explore the relationship between capture, infectious agents and fate, we simulated gillnet capture on adult salmon returning to a hatchery, used quantitative PCR to quantify infectious agents in non-lethal gill biopsies, and determined longevity, migratory fate, and migration rate using radio telemetry. An accompanying holding experiment investigated the relationship between infectious agents and longevity. Gillnetted fish took longer to migrate than biopsy-only fish (median 3.8 versus 2.5 days), but there was no difference in survival or migratory success among treatment groups. Longevity for fish infected with a parasite, Cryptobia salmositica, was similar between the holding (median = 7.0 days) and telemetry (7.4 days) experiments and significantly lower than that of uninfected fish (17.4 days in telemetry experiment). Males were 5.1 times more likely to arrive at spawning grounds compared to females and also migrated faster. The impact of C. salmositica on adult Chinook salmon in our study was demonstrated at the molecular (genes), physiological (plasma variables), and organism (migratory success) levels. These results demonstrate an instance where sex and infection were better predictors of migratory fate than an experimentally applied capture experience.
... For sardines [20] and herring [37][38], size is known to influence the survival rate following escape from fishing nets. This is caused by the higher susceptibility of smaller fish to be injured from the physical trauma associated with handling during fishing [9,[39][40]. In our experiment and compared to previous studies, the sardine size averaged 14.0 cm for all treatments, compared to 18.0 cm in [27] or 18.7 cm in [20]. ...
The release of unwanted catches (UWC) from purse seines, while the catch is still in the water, is known as “slipping”. Once thought to be a benign process, compared to discarding UWC overboard from the fishing vessel, it is now recognised that “slipping” can lead to significant mortality in the released fish if done inappropriately. In this chapter, we examine purse seining and slipping operations, and discuss what drives slipping and potential mitigation measures to reduce slipping mortality. We use three examples of purse seine fisheries for small pelagic species in the North-east Atlantic; from Norway, Portugal and Spain. The ideal solution (identifying and avoiding UWC before the net is set) requires the development of tools to enable fishers to better characterise target schools in terms of key selection criteria, e.g., with respect to species, individual size and catch biomass. Such tools are being developed, based primarily on hydro-acoustic technology. However, some UWC in purse seine catches are inevitable, and operational improvements in slipping practices have been shown to significantly reduce stress and mortality in the released UWC. We conclude with a discussion on the challenges currently facing the implementation of the European Union (EU) Landing Obligation with regards to minimising slipping related mortality.
... Ing olfsson and Jørgensen (2006) reported a high incidence of external and internal injuries to fish that were overrun by the rockhopper gear. The fate of injured escapees is not known, but it is generally believed that there will be some mortality due to behavioral impairment, increased risk of predation, and disease susceptibility caused by contact with the groundgear (Chopin and Arimoto 1995;Ryer 2004). It would therefore be beneficial for fishery management to limit the loss of Haddock below the fishing line during the capture process, thereby reducing potential mortality. ...
The catch efficiency of two types of groundgear—a conventional rockhopper and a new type of groundgear called the semicircular spreading gear (SCSG)—was investigated through experimental fishing for Haddock Melanogrammus aeglefinus conducted in the Barents Sea. A retainer bag was attached behind the footrope of the trawl, and the number of fish that were overrun by the trawl was compared with the catch in the trawl cod end. The catch efficiency increased slightly for larger Haddock for both groundgears. The SCSG was found to have a significantly higher catch efficiency than the conventional rockhopper groundgear. The estimated improvement in catch efficiency varied between 4.5% and 12.3%, with an equivalent reduction in escape rate underneath the groundgear of more than 70%. The rockhopper groundgear can have a catch efficiency as low as 76%, corresponding with values reported in previous studies. Average catch efficiency for the rockhopper gear was significantly lower during the night in comparison with the daytime. No such difference was found with the SCSG. The SCSG is more efficient for catching Haddock, and it is lighter than the rockhopper groundgear. Both are important factors in reducing seabed impact and fuel consumption. When compared to results of a similar study on Atlantic Cod Gadus morhua, we found that in general, both groundgears had a greater catch efficiency for Haddock, which accords with differences in behavior between the two species.
... The majority of the PIT-tagged adults that did not migrate successfully from Bonneville Dam to McNary Dam were rightfully harvested by Columbia River tribes as part of treaty fisheries implemented under the aforementioned voluntary abundance-based harvest schedule. It can also be surmised that some portion of the unsuccessful migrants died as the result of injury attributable to marine mammal bites (e.g., Fryer, 1998) or predation, gill net or angling wounds (e.g., Chopin and Arimoto, 1995), or injury from dam passage (e.g., Wagner and Hillson, 1993). Additionally, some of the unsuccessful migrants probably strayed permanently to non-natal locations downstream of McNary Dam. ...
This review summarizes what is known about the influence of water temperature and velocity on the migration and spawning success of an inland population of Chinook salmon Oncorhynchus tshawytscha. Models are then developed and used to illustrate how migration and spawning success might change if temperatures and velocities increase under a future climate. The illustration shows the potential for moderate increases in temperature and velocity to reduce homing and increase energy expenditure. Those two outcomes would reduce the abundance, productivity, and diversity of the population studied. Under the future scenario illustrated, it would become difficult for fish management actions alone to recover conservation-reliant populations of inland Chinook salmon.
Trammel nets are used with nearly five days of soaking time to increase the catching efficiency of demersal fish under the control of commercial fishers in the Marmara Sea, Türkiye. The long soaking times can be deteriorate or damage individuals of fish species and economic losses. In this situation, the length and weight of fresh individuals can be measured, but damaged individuals can not be measured in length and weight or both. These losses can be revealed by relating of the length–weight relationship. The current study aimed to determine economic losses by estimating the length–weight relationships of known length and weight of fresh individuals, and by calculating the weight of damaged individuals depending on the length–weight relationships. The catching operations with different soaking times were conducted firstly from December 2020 to December 2021 and secondly from the winter and spring seasons of 2022 in the Marmara Sea, Türkiye. A total of 654 individuals of all species were caught and 185 of them were determined to be damaged. This shows that 30% of those caught were damaged individuals. The total weight of the damaged individuals was calculated to be 91.3 kg. The damaged fish were caught with a total of 2000 m trammel nets and it was determined that they caused an economic loss of 355.3 USD. When we consider the decline and overexploitation of fish stocks, these economic losses and damaged individuals with long soaking times for trammel nets are significant. So, the negative effects of long soaking times on catchable stocks should be evaluated by fisheries managers, and the long soaking times of trammel nets should be regulated for sustainable fisheries.
Fishes are complex animals, with emotions, individual personalities and intelligence. Humans have wide-ranging impacts on the lives and welfare of fishes, but until recently we have given very little thought to the suffering we cause. This is beginning to change as the gap between public understanding and the science on fish intelligence closes. Governments are increasingly recognising sentience in fishes, and other marine animals like octopuses and lobsters, and are reviewing animal welfare legislation to better include them. However, with trillions of fishes killed each for food, addressing welfare in fisheries and aquaculture is complex, and fisheries in particular have largely been left in the ‘too hard basket’. It doesn’t have to be this way. There are solutions—we can keep feeding our growing populations whilst also ensuring fishes are treated with respect and compassion. It’s a journey we need to start as soon as possible
In this study, a series of commercial and experimental studies were carried out on factors that predict and affect the discard mortality, an important issue of fisheries management. The effects of mortality rates and pressure treatment on survival rate were observed in commercial trawl operations. Virtual fishing experiments were carried out in laboratory using live fish from the nature under controlled conditions. In these two different studies, survival rate, acute mortality and delayed mortality were estimated after a fishing operation. The main factors affecting the survival rate, fish behavior, pressure changes, trawling speed and seawater temperature. These factors showed different effects on different species.
The survival and mortality rates obtained as a result of experimental and marine studies were supported by biochemical blood parameters. The level of stress caused by factors affecting survival rate was determined by examining the amounts of cortisol, T3 and T4 hormones in the blood serum.
In the study, when pressure treatment was applied, the survival rate of the species was higher. In the trawl simulation and flow channel experiments, different sea water temperatures and behavioral impairment according to trawling speed and survival rates for 24 hours were determined. In these experiments, E. costae, E. aeneus, E. marginatus did not float in the net or in the flow channel and thus they were found to be alive without fatigue. L. mormyrus and S. aurata showed high swimming performance and were able to survive to a considerable extent when released to the water.
This thesis study showed that the discard survival rate is an important issue for sustainable fisheries and stock management. In addition, the survival of discarded fish released into the sea after fishing operations is an important issue for fisheries economic losses and responsible environmental approach.
High incidental catches of Greenland shark ( Somniosus microcephalus ) in Nunavut’s Greenland halibut ( Reinhardtius hippoglossoides ) fishery has led to studies on the feasibility of capturing Greenland halibut with baited pots. In this study, catch rates among six experimental pots are compared. In addition to this, underwater video observations of Greenland halibut interacting with two of these experimental pot types are quantified in order to help provide recommendations on future pot designs. Catch rates of Greenland halibut differed among pots with different entrance mesh types, and none of the pots produced substantial amounts of bycatch. Strings of pots were deployed within a narrow corridor between baited gillnets targeting Greenland halibut, which may have affected catch results. Video observations revealed Greenland halibut entangled by their teeth significantly more often in entrance funnels constructed with 50 mm than with 19 mm clear monofilament netting and the entrance rate was 45% higher with the 19 mm netting. Greenland halibut that successfully entered a pot repeatedly became entangled by their teeth in 58 mm netting used in the side and end panels and in a horizontal panel used to separate the pot into a lower and upper chamber. The majority (80%) of Greenland halibut were observed to approach a pot against the current. The downstream entrance was aligned with the current in 52% of the observed Greenland halibut approaches. Seventy percent of entry attempts and 67% of successful entries occurred when fish approached against the current and when the entrance was aligned with the current. These observations lead to recommendations that future studies consider developing a four entrance pot to ensure an entrance is always aligned with bottom currents. Based on these observations of entanglements, it is recommended to use 19 mm clear monofilament netting in the entrance funnel, 100 mm polyethylene netting in the exterior panels, and 19 mm polypropylene netting in the horizontal panel when targeting Greenland halibut. Three Greenland sharks were observed interacting with the pots in the video sets, but none were captured or damaged the pots during the potting experiments, providing validity to the use of pots to mitigate the capture of Greenland shark in Nunavut territorial waters.
After the Second World War, marine fishery industry was developed to a commercial industrial fishery by war torn countries to boost their economies. As a result, compared to traditional pole and line fishery , much larger fishing gears such as trawls and purse seines , and much larger and more powerful fishing vessels were built, and deployed to traditional fisheries grounds in the southern hemisphere. Although this led to an increase in the global marine catch in several folds, many fisheries around the world, however, have collapsed and depleted due to the over effort and overexploitation. Further, many marine resources have been destroyed as non-targeted by catch by ill-designed industrial scale fishing gears such as bottom trawls and purse seines. World-wide annual marine bycatch is around 27 million tonnes, and for bottom trawls 66–93% of the catch consists of bycatch while this is 64–79% for purse seine. Moreover, benthic marine environment around the world has been affected drastically by the bottom trawl fleet. Today, reduced industrial commercial fleet, and tough fishing regulations in developed countries have made a considerable progress towards reducing the fishing effort and hence the reduced bycatch and discards. Although modifications of industrial bottom trawls and purse seines have made a progress in reducing the bycatch to a certain extent, these fishing gears are fundamentally unsustainable. Customer interest on ‘sustainably caught’ fish and hence marine stewardship is increasing in developed countries. To this end, pole and line fishery should be propagated around the world as one of the best sustainable fishing method. Also, Ecosystem based fisheries management and small scale regional fisheries management should be the future approach in fisheries management as local knowledge on the local marine ecosystem can be used together with the participation of local fisher folks.
Experiencing pain is one of the key drivers of deciding whether to protect an animal under legislation and guidelines. Over the last two decades empirical evidence for fish experiencing pain has grown and this chapter reviews the current state of our knowledge. Defining animal pain has been problematic but a definition based upon whether whole animal responses to pain differ from non-painful stimuli and whether the experience alters future behavioural decisions and motivation is adopted. Studies show that fish have a similar nociceptive system to mammals, that behaviour is adversely affected and that this is prevented by pain-relieving drugs demonstrating that fish respond to pain in a different manner to innocuous events. Further, fish are motivated to avoid areas where pain has been experienced and are consumed by the painful event such that they do not exhibit normal fear or antipredator responses. Taken together these results make a compelling case for pain in fish. However, this topic is still debated and the chapter discusses the opposing opinions. If we accept pain occurs in fish then the wider implications of the use of fish must be considered. It would be in the public’s interest to keep fish healthy for a myriad of reasons including disease-free fish production, preventing zoonoses, conservation and sustainability of fish stocks and valid experimental results from laboratory studies using fish models.
This thesis provides an overview of recent selectivity studies conducted in eastern North Pacific trawl fisheries (e.g., West Coast groundfish bottom trawl fishery, Pacific hake [Merluccius productus] fishery, and ocean shrimp [Pandalus jordani] fishery). Collectively, these fisheries play a significant role in supporting fishing jobs, income, and coastal communities. However, bycatch can impact fishers ability to fully utilize the fisheries resource. Thus, developing gear modifications to reduce bycatch are increasingly important. In this thesis, results from VIII selectivity research papers addressing bycatch issues in eastern North Pacific trawl fisheries are presented.
In the U.S. West Coast groundfish bottom trawl fishery, constraining species such as darkblotched rockfish (Sebastes crameri), sablefish (Anoplopoma fimbria), and Pacific halibut (Hippoglossus stenolepis) bycatch can impact fishers ability to maximize their quota shares of healthier groundfish stocks. In Papers I-III, results from sea trials evaluating sorting grid bycatch reduction devices (BRDs) to reduce catches of these species are presented. Results from these papers demonstrate the ability of sorting grid devices to reduce bycatch while retaining a relatively high proportion of the targeted species. In Paper IV, the efficacy of T90 mesh codends to improve catch composition in the Dover sole-thornyhead-sablefish complex fishery were examined. In this fishery, where catches of juvenile and sub-adult sablefish are affecting fishers ability to achieve a higher ex-vessel value (e.g., landed value) of the sablefish resource, and higher attainment rates of Dover sole (Microstomus pacificus), results presented in Paper IV demonstrates that T90 mesh codends have potential to increase fishers opportunities to capitalize on their Dover sole individual fishing quota and enhance their net economic benefits while more effectively attaining their quota shares of sablefish.
In Papers V-VIII, results are presented from studies testing the efficacy of artificial illumination (e.g., light-emitting diodes [LEDs]) to reduce fish bycatch. In Paper V, research tested if simple enhancements to the visibility of a low-rise selective flatfish trawl headrope could improve bycatch reduction for darkblotched rockfish, sablefish and Pacific halibut. Findings from Paper V suggest that use of illumination could have potential applications for reducing bycatch under particular situations. For example, fishers seeking to reduce sablefish catches and/or Pacific halibut bycatch when targeting English sole (Parophrys vetulus) and petrale sole (Eopsetta jordani) could potentially benefit from illuminating the trawl headrope, whereas fishers seeking to target Dover sole and/or sablefish but avoid darkblotched rockfish, would likely not benefit from using illumination. In Papers VI-VII, studies evaluating the efficacy of LEDs to reduce eulachon (Thaleichthys pacificus) and groundfish bycatch were examined. For eulachon, an anadromous smelt species endemic to the eastern North Pacific, their bycatch is an issue facing the ocean shrimp fishery as the species’ southern Distinct Population Segment was listed as “threatened” under the U.S. Endangered Species Act (ESA) in 2010. Results presented in Papers VI and VII continue to support the hypothesis that there is a significant reduction in eulachon bycatch when artificial illumination is present. For rockfishes and flatfishes, findings suggest their ability to escape trawl entrainment in response to illumination along the fishing line is not as strong as previously indicated. As conservation of ESA-listed eulachon is an ongoing management priority, Papers VI and VII contribute new data on the efficacy of footrope illumination to reduce their bycatch. Lastly, Paper VIII conducted two separate experiments evaluating the influence of artificial illumination on Chinook salmon (Oncorhynchus tshawytscha, a species with ESA listings) behavior and escapement out of a BRD in a Pacific hake midwater trawl. Findings from Paper VIII demonstrate that artificial illumination can influence where Chinook salmon exit out the BRD tested, but also that illumination can be used to enhance their escapement overall. Because ocean distributions of Chinook salmon and Pacific hake often overlap, interactions between Pacific hake trawl gear and Chinook salmon are likely to continue to be an issue facing the fishery. Findings from Paper VIII provides data on a gear modification that can minimize Chinook salmon bycatch.
Lastly, the collective work presented within this thesis has contributed substantially to the development and advancements of gear modifications for reducing bycatch in eastern North Pacific trawl fisheries and the conservation of ESA-listed species.
Papers I, II, and VIII are published in Fisheries Research, Papers III, IV, and V are published in Marine and Coastal Fisheries, Paper VI is published in the International Council for the Exploration of the Sea Journal of Marine Science, and Paper VII is published in the Canadian Journal of Fisheries and Aquatic Sciences.
Scientists have built a significant body of research that shows that fishes display all the features
commonly associated with intelligence in mammals, and that they experience stress, fear and pain. These
findings have significant ramifications for animal welfare legislation, an area from which fishes have been
traditionally excluded. Our most detrimental interaction with fishes is through commercial fisheries and
aquaculture, an industry that feeds billions of humans and employs millions more. We have invented a
vast array of fishing methods that extract fishes from almost every region on the planet in an equally vast
range of violent and painful ways. Fisheries managers regularly fail to prevent overfishing to ensure
healthy populations of target species, have not adequately addressed the impacts on other marine
species and the broader environment, nor prevented human rights abuses on board fishing vessels. Fish
welfare has not been a consideration. Farmed fishes are under our control for their entire lives, and while
there are welfare guidelines available, where these are applied, the goal is primarily to maximise
production and reduce losses, rather than ensure good welfare. These industries are important to many of
us; however, we need to change these systems to address both welfare and sustainability. For fisheries
this means a reduction in the number of fishes killed, by addressing overfishing and wasteful capture
methods, and reducing the length of time fishes suffer during capture. For aquaculture this means
keeping fishes in more natural environments at lower densities, reducing transport and handling impacts,
and choosing species that cope better with farming. Both sectors need to develop humane slaughtering
practices. Fish behaviour and welfare experts will benefit from working with the people and systems that
are driving more ethical and sustainable practices in fisheries and farming, to help initiate improvements
that will benefit individual fishes and the broader marine environment, as well as the lives of those
working in the industry. We must ensure that where we do need to farm and capture fishes it is done
humanely, fairly and without unnecessary waste of trillions of lives. A simple way forward would be to
reduce our reliance on fish as a primary source of protein, particularly in wealthy countries where
alternatives abound.
Conventional harvest techniques used in mixed‐stock commercial salmon fisheries frequently result in bycatch mortality, impeding salmonid recovery and constraining fishing opportunities in the U.S. Pacific Northwest. To address the problem, a post‐release survival study was conducted in the Columbia River to evaluate the potential of an experimental salmon trap for stock‐selective commercial harvest. A modified fish trap was constructed and operated from August through September 2017 with the goal of minimizing entanglement, air exposure, crowding, and handling of all captured fishes. Post‐release survival from the trap was estimated through a paired release–recapture study. Results demonstrate that the trap effectively targeted commercially viable quantities of hatchery‐origin Chinook Salmon Oncorhynchus tshawytscha and Coho Salmon O. kisutch while reducing bycatch mortality rates relative to conventional commercial fishing gears. During the study, 7,129 salmonids were captured. The post‐release survival effect over a 400‐km migration ranged from 0.944 (S͡E= 0.046) for steelhead O. mykiss to 0.995 (S͡E= 0.078) for Chinook Salmon, supporting the potential application of traps for stock‐selective commercial harvest. This article is protected by copyright. All rights reserved.
Background
The red swamp crayfish, Procambarus clarkii (Girard, 1852), is one of the most promising freshwater species for aquaculture in China. Understanding its reproductive pattern and population dynamics is crucial for sustainable management, but there is currently a lack of fundamental knowledge of commercial P. clarkii populations. Therefore, the purpose of this study was to investigate the reproductive pattern and population dynamics of commercial P. clarkii throughout the yearly cycle.
Methods
A total of 2,051 crayfish (1,012 females and 1,039 males) were collected from March 2016 to February 2017 in the area of Selection and Reproduction Center of Crayfish. The reproductive pattern was evaluated by the gonadosomatic index (GSI), hepatosomatic index (HSI), ovarian development and fecundity. Growth, mortality rates and exploitation rate were estimated by electronic length frequency analysis by R package “TropFishR” based on data of cephalothorax length (CTL).
Results
Our results demonstrated that spawning activities of P. clarkii took place from September to November, with a mean fecundity of 429 ± 9 eggs per female. There were two recruitments yearly, a major one from October to November and a minor one from March to May. With respect to population growth, five growth cohorts were identified for both females and males. Crayfish grew faster but attained smaller asymptotic maximum CTL as indicated by higher growth coefficient ( K ), growth parameter index ( Ø ′) and lower asymptotic CTL ( L inf ). The estimates of total mortality rate ( Z ), natural mortality rate ( M ) and fishing mortality rate ( F ) were 1.93, 1.02, 0.91 year ⁻¹ for females and 2.32, 0.93, 1.39 year ⁻¹ for males, which showed that the mortality of male crayfish was mainly caused by fishing. The estimates of exploitation rate ( E ) indicated that male crayfish were overexploited, with the values of 0.47 and 0.60 year ⁻¹ for females and males, respectively.
Discussion
P. clarkii spawned from September to November while two recruitments were observed yearly. We inferred that some eggs, prevented from hatching by low water temperature in winter, were more likely to hatch in the next spring. Moreover, the fishing mortality rate was relatively high for males, which might be related to the males-directed selection during the reproductive period. The higher values of exploitation rate in our study confirmed that males P. clarkii were overexploited and were under high fishing pressure. We thus suggest reducing fishing intensity on immature crayfish and avoid sex selection during the reproductive period to improve the overall sustainability of commercial P. clarkii populations.
To assess the effectiveness of a proposed minimum size limit (81 cm) for Atlantic halibut (Hippoglossus hippoglossus) in Canadian waters, the survival of small fish caught in longline and bottom trawl gear was examined using live holding facilities onboard a research vessel and subsequently, in a land-based laboratory. Commercial practices were simulated during fishing operations. Of halibut less than the proposed size limit, 35% of the otter trawl catch and 77% of the longline catch survived more than 48 h. Factors potentially influencing halibut survival (handling time, total catch, fish length, maximum depth fished, and trawl duration) were examined using proportional hazard models. On the basis of those analyses, it was concluded that in bottom trawl sets of duration used in the commercial fishery (≥ 2 h), higher survival times were associated with shorter handling time, larger fish size, and comparatively small total catch weight. Supplemental information on the condition of trawl-caught halibut was also obtained from observers stationed onboard commercial trawlers.
King crabs Parali thodes ca1ntschaticus and Tanner crabs Chionoecetes bairdi captured incidentally by Bering Sea trawlers were examined for immediate mor tality, vitality, and injuries resulting from trawl capture. A number were held aboard ship for 2 days in sea water to determine delayed mortal ity. Overall survival, including imme diate and delayed effects, was 21% (±2.0%) for king crabs and 22% (±3.6%) for Tanner crabs. Immedi ate mortality of king crabs decreased significantly with shell age, and in creased significantly with time in captivity prior to assessment, from 0% at 3 hours to 100% at 17 hours. Vitality, an index of spontaneous ac tivity level, was a better predictor of delayed mortality than was the pres ence/absence of injuries. The effect of leg and body injuries on mortal ity of king crabs was similar, but in juries to leg segments proximal to the plane of autotomy resulted in higher mortality than injuries distal to the autotomy plane, or autotom ization alone. Capture and subsequent mortality of nontarget (bycatch) species is a major problem facing managers of multi species fisheries. In the U.S. eastern Bering Sea (EBS), joint-venture (JV) trawl fisheries targeting on yellowfin sole Limandaaspet"a, rock sole Lepi dopsetta. bilineata., and Pacific cod Gadus macrocephalus, routinely catch red king crabs Paralithodes camtschaticus and Tanner crabs Chi onoecetes bai1'di and C. opilio. In 1988,88000 red king crabs, 751000 C. bairdi, and 2.4 million C. opilio were captured in 1.30 million metric tons (t) of groundfish by JV fishing vessels, representing catch rates of 0.07, 0.58, and 1.84 crabs/t, respec tively (Berger and Weikart 1989). Additional quantities of these crab species were also captured by domes
The efficiency of an 8-ft scallop drag was estimated from population density measurements by scuba divers. Density measurements had to be made with an enclosed quadrat because of scallop swimming activity. Scallops responded to approaching objects by facing away from them and swimming. A steep rise usually preceded level swimming at a mean height of 0.4 m from bottom. Point-to-point swimming distances of up to 4 m were recorded with ground speeds in excess of 67 cm/sec. Few scallops over 100 mm could be induced to swim.Despite level bottom conditions, overall drag efficiency was low (2.1%) but increased progressively over the size range encountered (20–150 mm). Direct observations of drag function showed that swimming activity rather than selection by the drag was responsible for the low drag efficiency for the capture of scallops smaller than 100 mm.An indirect fishing mortality was established for recessed scallops buried by the drag. Dragging resulted in dislodgement of dead shell to the substrate surface, and aggregation of benthic predators in the drag tracks.
The success of no-kill regulations for salmonid fisheries has led to increased interest in applying them to warmwater fisheries. Hooking mortality often makes gear restrictions critical to the success of these regulations. The objective of this study was to determine the probability of death (hooking mortality) for smallmouth bass Micropterus dolomieui caught on live minnows and artificial spinners. We collected 55 wild smallmouth bass from 6.3 to 12.6 in long and tagged them for individual recognition. We divided them into approximately equal groups and released them into artificial stream channels. During four 2-week test periods, we hooked and released fish in one channel using live minnows on a single hook and in the other channel using a spinner with a treble hook. Some fish in each channel were not hooked during the study. Mortality was 11% for smallmouth bass hooked on minnows, 0% for those hooked on spinners, and 4% for those not hooked. Mortality of fish hooked with minnows was significantly greater than mortality of either spinner-hooked or unhooked fish (P < 0.05); the latter two mortalities did not differ significantly. Some fish were caught numerous times, and others were never caught. If other types of natural baits and artificial lures also give similar results, it may be necessary to restrict fishing gear to artificial lures to ensure success of no-kill fishing regulations for smallmouth bass.
Capture by angling was used to induce burst exercise in northern pike. By 3 h after exercise blood lactate had risen to levels
of 15.2 mmol l−1 (Fig. 2), which greatly exceeded the maximum post-exercise levels (4.0 mmol l−1) previously reported for muskellunge, a close relative of pike. White muscle lactate level was high, 41.8 mmol kg−1, immediately after capture but declined to 23.2 mmol kg−1 by 6 h (Fig. 2). Blood glucose level more than doubled after exercise and remained elevated even after 96 h of recovery (Fig.
2).
During the first 6 h after angling, pike disposed of 9.57 mmol (861 mg) of lactate per kg body weight. A whole body metabolic
rate of 153 mg O2 kg−1 h−1 is sufficient to account for this rate of lactate removal through oxidation (Table 3). However, the metabolic rate of the
highly oxidative organs and tissues (red muscle, gills, liver, kidney, heart, and spleen) must be very high (>1,000 mg O2 kg−1 h−1) to oxidize even 60% of the lactate that disappeared from pike after exercise (Fig. 5).
Mortality of pike from angling stress was less than 3%.
American lobsters taken in the commercial trawl fishery in Long Island Sound. U.S.A., were in spected for incidence ofdamage and immediate mortality associated with bottom trawling. Similar sampling was conducted in the pot fishery. American lobsters from trawl and pot catches were held in controlled conditions for 14 days to determine the level ofdelayed mortality associated with the two fisheries. Trawl-caught lobsters were exposed to subfreezing (-9.5·Cl temperatures for periods from 30 to 120 minutes and then returned to seawater to determine the rate offreeze-induced mortality. Major damage rates due to trawling ranged from 12.6-14.0% during molting periods to 0-5.6% during intermolt periods. Delayed mortality ranged from 19.2% during the July molt to 1% during August and appeared to be related to the incidence ofdamage, molt condition, and temperature. Mortality of American lobsters held in subfreezing temperatures occurred after 30-minute exposure and reached 100% at 120-minute exposure.
Hooking mortality was examined in a population of wild cutthroat trout (Salmo clarki bouvieri) in a portion of the Yellowstone River, Yellowstone National Park, which is managed under catch-and-release regulations. The number of trout dying from capture and release in the 4.5-km study area was assessed by searching for trout carcasses in established snorkeling routes. We divided our estimate of angler-induced mortalities by cutthroat trout abundance and creel survey data to estimate single capture hooking mortality and exploitation rates resulting from catch-and-release angling in the study area. The average number of times cutthroat trout were recaptured during the study period was estimated from the results of the creel survey and cutthroat trout abundance data. The hooking mortality rate per single capture was 0.3%. In 1981, 3% of the estimated cutthroat trout population died after capture and release by anglers. Cutthroat trout in the study area were captured an average of 9.7 times during the study period in 1981.
This study evaluated the physiological response of rainbow trout to hooking stress after being played under standardized conditions (0–5 min) and estimated the time needed for recovery (to 72 h). Plasma osmolality and chloride measurements were used to evaluate osmoregulatory disturbances and gill ion-exchange function, and plasma glucose was used as an index of the generalized nonspecific physiological stress response. Hooking stress caused more severe blood chemistry differences in hatchery fish than in wild trout. Also, hooking stress imposed a greater stress on larger than on smaller hatchery rainbow trout. Higher water temperatures aggravated the delayed hyperglycemia and hyperchloremia in both hatchery and wild trout but only about 3 days were needed for recovery at 4, 10, or 20 C.
Immediate and short-term (1–5-d) hooking mortality associated with the incidental catch of chinook salmon Oncorhynchus tshawytscha was assessed during periods when troll fishing for that species (only) was prohibited. Two chartered power trollers fished their normal complements of gear directed at coho salmon O. kisutch in Hawk Inlet, southeastern Alaska. Wound location, fork length, and lure type were the factors principally associated with mortality of incidentally caught chinook salmon. Severity of the hooking wound was also related to mortality. Maximum-likelihood estimates (with 95% confidence intervals in parentheses) of total mortality were 24.5% (20.1–29.0%) for sublegal-sized (
The mortality of age II hatchery-reared landlocked Atlantic salmon (Salmo salar) hooked on four types of fishing gear was evaluated by conducting experiments at the Casco and Grand Lake (Maine) Fish-cultural Stations, in spring 1976-78. An additional experiment to evaluate mortality of fish purposely deep-hooked on worms was conducted in 1978. Of 1221 fish caught on all gear types, only 5% died after hooking; less than 1% of the 300 control fish died. No significant differences (χ², P < 0.05) were demonstrated in mortality among the four gear types (treble- and single-hook hardware lures, flies, earthworms). Of total mortalities, 89% died within 24 h. Of 106 salmon purposely allowed to swallow worm baits, 73% died. Of 56 fish in which the hook was left in place and the leader cut at the mouth, 57% died during the 14-day holding period. A significantly greater mortality (90%; cho², P < 0.05) was experienced for 50 deeply hooked salmon from which hooks were removed. Reasons for possible underestimation in mortality for worm-hooking experiments in hatcheries are discussed.
Catch size and oxygen concentration affected survival of commercially seined fresh-water drums Aplodinotus grunniens intended for release back to Lake Erie or for live transport to fishing ponds. Survival was inversely related to the time that fish in beached seines were exposed to deoxygenated water and, in general, survival was greater in smaller catches (1-3 tonnes) than in larger catches (7-30 tonnes). Dissolved oxygen (DO) concentrations declined drastically with the length of time fish remained in the beached seine and with increased catch size. Fish sampled from water with more than 6 mg DO/L had greater survival than fish taken from water with 2-6 mg DO/L; oxygen levels below 2 mg/L were associated with high mortality. Survival was not related to water temperature (14.5-19.5°C), and large fish were less affected by seine capture than were smaller fish. Maintenance of oxygen levels in the seine by encouraging water flow into the beach seine, direct delivery of oxygen, or less crowding of captured fish are proposed to improve survival of released fish. A model to predict the survival of released fish indicated that approximately 85% of the freshwater drums die after release from Sandusky Bay (Ohio) shore seines during the spring fishing season.
Fingerling rainbow trout, acclimated to hatchery raceways or laboratory aquaria, had low plasma cortisol levels (≤ 2 ng/mL), with no apparent daily cycle in levels. Netting of cohorts out of an aquarium, without agitation, did not cause a rise in plasma cortisol concentrations in remaining fish. However, following 90 s of handling and confinement by netting, fingerlings had a sharp rise in plasma cortisol to a peak at 15 min, and then a gradual decline to the basal level over 2 h. Gentle agitation and intermittent restraint with a dip net in the aquarium caused a gradual increase in plasma cortisol concentrations. Intense handling and severe confinement caused a rapid increase in plasma cortisol to a plateau, two to four times greater than the peak levels found in fingerlings subjected to the less vigorous stressors; high levels of plasma cortisol were maintained to the median tolerance limit. During a stocking operation, there was a rapid rise in plasma cortisol concentrations during the initial capture from the rearing ponds, and high levels were maintained through to stocking into the lake 6 h and 10 min later, although a small decrease occurred during transit while the fish were in the truck tanks. After stocking, plasma cortisol concentrations in caged fingerlings did not decrease to the basal level until 8 d poststocking.Key words: rainbow trout, fingerlings, plasma cortisol, cycles, handling stress, stocking stress
Snapper (Pagrus auratus) were captured and their blood was sampled underwater by SCUBA divers.
Cortisol concentrations in normally active fish ranged from 1.7 to 8.0 ng mL-1, with concentrations
being highest in winter during the period when fish were sexually regressed. Underwater confinement
in a net led to measurable increases in plasma cortisol (27 ng mL-1) by 60 min after capture. Fish
captured by rod and line and confined in a 200-L tank on board the capture vessel showed a similar
response latency. Further fish were captured by longlining or trawling and confined as before for
periods of up to 1 h. Fish captured by a longline set for 1.5 h had initial mean plasma cortisol
concentrations of 22 ng mL-1. These increased further over 60 min to a maximum of 58 ng mL-1.
There was no difference in plasma cortisol between fish that were serially sampled or bled only once,
indicating that increases in cortisol concentrations were due to capture stress and not the handling
protocol. Plasma cortisol concentrations in fish taken by longlines set for up to 12 h remained high,
showing that recovery from stress did not occur in fish left on the longline. Trawled fish showed
similar increases in plasma cortisol, with concentrations reaching 42 ng mL-1 at 60 min after capture.
Fish transferred to a 3000-L holding tank in the laboratory following capture by longline initially had
high plasma cortisol concentrations (70 ng mL-1) . Concentrations remained high for at least 12 h
but fell to 9 ng mL-1 after 48 h in the laboratory. The possible consequences of elevated cortisol
concentrations for fish husbandry after capture and for post-mortem tissue quality are discussed.
Gillnet selectivity in the Pacific herring roe fishery was examined using experimental apparatus. Estimates of size-specific selectivity of monofilament gillnets were calculated by comparing numbers and lengths of fish retained in nets with those that swam through the net into a trap. Most fish less than 19 cm were not captured; most fish greater than 21 cm were captured. Factors affecting selectivity included size, sex and maturation (or gonad size). There was also a difference in selectivity between locations, perhaps associated with biological differences between populations. Fish that swam through the nets suffered little injury and scale-loss. Laboratory and field tests indicated high survival of fish that encountered, but were not captured by, the nets. Estimates of long-term survival were unavailable because disease became widespread throughout the holding facilities.
Series of trials in which mackerel (Scomber scombrus L.) were confined in keepnets at different stocking densities are described. From simple confinement trials it was found that 50% of the fish died after 48 h at a stocking density of 30 fish m−3, equivalent to 6.5 kg m−3. Trials in which fish were held at stocking densities, and for a duration, comparable to those experienced in a “dried up” purse seine prior to “slipping”, showed that up to 90% of “slipped” fish died within 48 h of release. The primary cause of death was probably physical damage, particularly skin loss, caused by abrasion, although there is some evidence that mackerel have a healing process which can accommodate minor skin abrasions. A tagging trial showed a small but significant increase in mortality due to the tagging procedure.
Tracks of three types of fishing gear in bottom sediments were observed from a submersible in Chaleur Bay (Gulf of St. Lawrence). Tracks left by past otter trawling activities covered at least 3% of the bottom by area and were considered to have been made by trawl doors.Shallow tracks made by inshore and offshore scallop dredges during the course of the study could be distinguished from each other and from trawl tracks.Scallop dredging lifts fine sediments into suspension, buries gravel below the sand surface, and overturns large rocks embedded in the sediment, appreciably roughening the bottom. The inshore Alberton dredge is inefficient, dumping its contents back onto bottom at intervals during the tow.Dredging causes appreciable lethal and sublethal damage to scallops left in the track, this damage being greatest on rough bottom. Incidental mortalities to scallops with an offshore dredge of at least 13–17% per tow are of the same order of magnitude as estimates of harvesting efficiency made in earlier studies.Predatory fish and crabs were attracted to the dredge tracks within 1 hr of fishing and were observed in the tracks at densities 3–30 times those observed outside the tracks.
1.1. This paper describes the measurement of whole blood lactate, glucose and Cortisol concentrations in mackerel subjected to a number of Stressors: capture by hooking, confinement in tanks or floating net enclosures, overcrowding in purse seine net simulation trials and tagging with internal metal tags.2.2. The physiological changes induced by the different Stressors followed a pattern expected from work with other teleosts.3.3. Some stressed mackerel were observed to change their skin colour from green to blue, the “normal” colour of a dead mackerel. However, no correlation of this change with the blood component measurements or the type of Stressor applied was found.4.4. There was no correlation between the blood component values and the degree of skin loss suffered by some fish.5.5. Estimates of the “normal” concentrations of whole blood lactate, glucose and Cortisol are given.
This book presents the latest information on fishing methods and gear and their applications for the capture of different species. In particular it reflects the increased awareness of the developments in commercial fishing which have evolved, and continue to evolve, in answer to the urgent need to protect endangered species, to eliminate by-catch, and to protect juvenile and under-sized fish. New designs for vessels are covered, and the increasing use of combination vessels able to work several gears in order to meet modern resource management requirements is outlined.
Plasma corticoid concentrations in juvenile chinook salmon (Oncorhynchus tshawytscha) netted and confined in a small live-cage rose from approximately 100 ng/ml to about 500 ng/ml in 24 h, then fell to 250 ng/ml at 48 h. In juvenile chinook salmon dip netted into a bucket containing aerated water and sampled serially at 90-s intervals, plasma corticoids increased from < 10 ng/ml to approximately 100 ng/ml in 20 min. In juvenile cutthroat trout (Salmo clarki clarki) acclimated to 13 C and subjected to a rapid increase in water temperature to 26 C, plasma corticoid concentration increased from about 20 ng/ml to 70 ng/ml in 25 min and remained elevated for more than 3 h. Juvenile cutthroat trout acclimated to diurnal temperature cycles (13–23 C) had no substantial changes in plasma corticoid concentration throughout the cycles. Juvenile cutthroat trout acclimated to 23 C had the same initial corticoid concentration as cutthroat trout acclimated to 9 C. When both groups were subjected to identical netting and confinement, the corticoid concentrations in fish from the two temperatures responded in a similar fashion until 70 min of confinement when trout from the warmer water failed to maintain increasing corticoid concentrations.
The physiological factors affecting the survival of demersal fish caught by trawl and Danish seine were considered in relation
to initial tagging mortality. Experiments using haddock that were confined in sea-bed cages showed that the initial mortality
was greater when the fish had been taken to the surface after capture than when they were transferred directly from the codend
to a sea-bed cage. It is probable that the main factors responsible for causing initial mortality in those fish that had been
taken to the surface were physiological shock and fatigue together with swimbladder damage; together these factors rendered
the fish extremely vulnerable to any adverse environmental conditions when they were returned to the sea-bed. Tagging itself
was considered to be a comparatively minor contributant to initial mortality.
Mortalities of hooked and released trout were measured at four Montana state hatcheries in 1978. At Yellowstone River Trout Hatchery, cutthroat trout (Salmo clarki) caught by single-barbless, single-barbed, and barbed treble hooks and landed rapidly showed no significant mortalities. At Washoe Park Trout Hatchery, Big Springs Trout Hatchery, and Bluewater Springs Trout Hatchery, rainbow trout (Salmo gairdneri) caught and returned to water of five different temperatures (47-61 F) showed mortalities that increased from 0 to 8.6% with increasing water temperatures. All fish in temperature-related tests were played to exhaustion before release.
Moving 4–5-in. coho salmon (Oncorhynchus kisutch) held in soft (20 ppm CaCO3) water from the relatively light loading density of 0.5 lb/ft3 to 1, 2, or 4 lb/ft3 (density index, DI = 0.1, 0.2, 0.4, 0.8) caused significant stress as indicated by loss of feeding behavior, but only minimal physiological disturbances, as indicated by lack of hyperglycemia or hypochloremia. However, moving them to 6 or 12 lb/ft3 (DI = 1.2, 2.4) caused significant physiological stress which required at least a week for recovery. Smolting coho salmon were physiologically stressed by population densities of 1 lb/ft3 or more and a subclinical corynebacterial kidney infection was activated. Rainbow trout (Salmo gairdneri) (4–5 in.) were physiologically stressed when moved and held at 1 lb/ft3 or more but retained normal feeding behavior. This indicates that handling and crowding stress will be minimized in softwater areas if densities in fish distribution trucks or in ponds or raceways during disease treatments are held to 0.1–0.5 lb/gal.
Mortality (other than landed catch) caused by pelagic gillnetting is estimated to be equal to the catch, for salmon in their penultimate year of life, and equal to about a quarter of the catch for salmon in their final year of life. Mortality caused by trolling for coho (Oncorhynchus kisutch) and chinook salmon (O. tshawytscha) averages about one fish killed (mostly below legal size) for every two that are boated. The natural mortality rate for sockeye salmon (O. nerka) in their final year of life averages about 0.015 per mo and is somewhat more in earlier years of pelagic life; the greater part of natural mortality after the smolt stage occurs during the downstream migration and early months of "coastal" life. For coho and chinook the best natural mortality estimate for the last year of life is 0.013 per mo, and that for pink (O. gorbuscha) and chum (O. keta) is of the same order. Growth rates during the final growing season vary from 0.26 per mo for pink and coho salmon to 0.06 per mo for chinook in their 5th ocean yr. Gains from ceasing to take immature salmon on the high seas range up to 300% of the catch now being taken in that category, while for fish taken in their final year they range up to about 70%, depending on the time of year at which the fishing is done. Gains from transferring existing pelagic net fisheries to the coastal region would be 76% (North American sockeye) and 86% (Asian sockeye) of the weight of fish now caught pelagically. Gains in total yield of existing salmon fisheries (pelagic and coastal) are estimated as 78% for Asian pink salmon and 72% for Asian sockeye. The increase in weight of the total catch from discontinuing ocean trolling for Columbia River chinook salmon and increasing river fishing correspondingly is estimated tentatively as between 63 and 98%.
Capture by trolling subjects feeding coho and chinook salmon to hyperactivity which may lead to a distressed condition or death, and death cannot be predicted from examination of individual fish at time of capture. Mortality of coho was estimated to be in the 0.95 confidence interval of 34% and 52%. Time of maximum death rate of coho is shown to coincide with the period of maximum blood lactate response. Survival occurred either when blood lactate did not reach critical levels (above 125 mg%) or reached critical levels and subsequently subsided. Holding salmon in a live box for 8–14 hours before release did not improve tag recovery, suggesting additional indiscriminant stress was caused at release. Adult coho in fresh water did not appear capable of lethal hyperactivity. This led to the hypothesis that cessation of feeding during spawning migration has adaptive significance for survivial of Pacific salmon.
Between 1984 and 1987, more than 30,000 striped bass Morone saxatilis were captured for tagging in the Hudson River, New York, with trawls and seines. Handling before tagging was the major source of mortality. Immediate mortality decreased from 16.1 to 1.2% for striped bass captured in seines and from 17.7 to 1.0% for striped bass captured in trawls when the handling procedure was modified. The modified procedure involved guiding the cod end into a partially submerged holding tank beside the capture vessel instead of lifting the cod end out of the water to transfer the catch to a holding tank aboard the capture vessel. A significant interaction between immediate mortality, water temperature, and fish length was observed before the handling procedure was modified but not afterward. When the unmodified handling procedure was used, immediate mortality increased with increasing fish length and water temperature. However, recapture rates within a year after release also increased with increasing water temperature at the time of tagging. No significant interaction between recapture rate, water temperature, and fish length was observed for striped bass when the modified handling procedure was used. The significantly lower recapture rate for striped bass when the modified handling procedure was used (3.8%) than when the unmodified handling procedure was used (7.2%) appeared to be due to a change in harvest regulations, not to higher delayed mortality.
Adult striped bass Morone saxatilis were captured in 20–40-min gill-net sets in the San Joaquin River, California, and in 24–48-h fyke-trap sets in the Sacramento River as part of a tagging program. They were bled by cardiac puncture for various measurements of stress responses to capture and handling. Fish caught in gill nets were more lethargic, were kept longer out of water, and were significantly more acidotic (lower blood pH and higher lactate concentration) than fyke-trapped fish. Gillnetted fish also had a significantly higher Pco2, hematocrit, and plasma glucose and potassium concentrations than fyke-trapped fish. Both capture methods induced secondary stress responses, but responses were greater in gillnetted fish, probably because gill nets restricted buccal and opercular movements.
Attempts to establish a put-grow-and-take fishery for rainbow trout (Salmo gairdneri) in Jocassee Reservoir, South Carolina failed despite plantings of 200,000 fish in 1972-1979 because few of the stocked fish survived to legal size. At the same time, a fishery for brown trout (Salmo trutta) was established successfully by planting far fewer fish. Experiments were conducted to determine if stress at stocking and injuries and stress associated with catch and release of fish by shoreline anglers were responsible for the poor survival of rainbow trout. Only 1 of the 606 rainbow trout stocked in floating wire cages anchored in the reservoir died during the first 3 days, and fewer rainbow trout than brown trout died as a result of catch-and-release fishing during the first 11 days after stocking. Thus, these factors were not responsible for the lack of success in establishing a rainbow trout fishery in this reservior.
The catching efficiency of the Astralian scallop “mud” dredge was examined in two experiments on plots seeded with scallops (Pecten fumatus) of known size and abundance. Catching efficiency was found to be low: on average only 11.6% of the reseeded scallops in the tow path were caught. Size selectivity ranged from 1% for scallops of 57 mm shell height, to 28% for scallops of 86 mm shell height. The efficiency of the dredge was not affected by either the dredge mesh size, or the direction of tow with respect to orientation of ripples and sandwaves on the sea-bed.To determine the mortality of scallops resulting from the use of this dredge, changes in the relative proportions of live, damaged and dead scallops on the Banks Strait grounds before and after the start of the 1986 fishing season were measured by assigning scallops from subsamples of catches to one of the three categories. At the start of fishing, both scallop density and levels of shell damage due to dredging were high. Although the proportion of damaged scallops in catches declined over time, a high mortality rate of scallops continued after commercial fishing had ceased. This rate was such that almost all the remaining scallops on the bed were dead within 8 months of the closure of the grounds.A general theoretical model describing changes in the proportions of live, damaged and dead scallops as a consequence of dredging is presented. The model indicates that only 12–22% of the initial stock in Banks Strait was landed as catch, with the rest of the stock wasted through direct and indirect mortality resulting from dredging.
Coho salmon (Oncorhynchus kisutch) were caught with sport gear in the estuary of the Little Susitna River, southcentral Alaska. Fish were double marked and released. All coho salmon observed migrating through a weir above the estuary and a portion caught in a sport fishery below the weir were examined for marks. A second group of coho salmon were caught using similar sport gear above the estuary. These fish were handled and marked identically as the fish captured in the estuary, except that they were held in a holding pen at the weir with an equal number of coho salmon dip netted at the weir. Coho salmon which were caught and released in the estuary suffered a significantly higher rate of mortality (69%) than did either the coho salmon caught and held above the estuary (12%) or those which were dip netted and held at the weir (1%). Factors that could influence rates of hook-induced mortality were measured at the time of hooking. Hook location, hook removal, and bleeding significantly affected the measured mortality rate.
The fate of by-catch discarded by the Moreton Bay prawn trawl fishery was studied between September 1983 and March 1986. The composition and biomass of the by-catch were ascertained and the effect of trawling and handling on its survival was measured. The by-catch was made up of 52% crustaceans, 15% elasmobranchs, 8% bony fish, 18% echinoderms, 3% cephalopods and 4% debris by weight.Trawl hauls lasted about 60 min. and the catch was sorted in about 20 min. About 85% of the Crustacea and about 20% of the bony fish were still alive 8 h after sorting.
A consiituent feature of the response of salmonid fish to most forms of environmental stress is an activation of the hypothalamic-pituatary-interrenal (HPI) axis, resulting in the secretion of the steroid hormone cortisol, into the bloodstream. This is part of an adaptive response in which corti