Short-Term Mortality of Discarded Finfish Bycatch in the Gulf of Maine Fishery for Northern Shrimp Pandalus borealis

Review and evaluation of fishing-related incidental mortality for Pacific salmon

Technical Report

Full-text available

May 2017

The number of fish that encounter fishing gear is greater than the number of fish retained as catch. The proportion of this difference that die from the encounter is defined as fishing-related incidental mortality (FRIM). FRIM estimates are required for improved stock assessments, but they are difficult to attain and vary across fisheries. To cope with this challenge we review and evaluate the scientific knowledge on FRIM. First, we review the different mortality components of FRIM (i.e., avoidance, escape, depredation, drop-out, on-board, short-term release, and delayed mortality) in relation to how a fish responds to different aspects of a fishery encounter (e.g., handling). To better understand how fish respond to a fishing encounter, different fishing factors (e.g., gear type) that act in consort with extrinsic (e.g., water temperature) and intrinsic (e.g., fish size) factors elicit different fish responses that can lead to the different types of mortality (e.g., acute) were examined. A fish response to a stressor (i.e., factor) is a combination of the magnitude and duration of the stressor itself. The initial fish response includes acute physiological stress and injury, followed by behaviour changes, chronic stress, and increased risk of infection. Next, a review was done to provide an up-to-date accounting of the mortality rate information available on estimates of FRIM for Pacific salmon (Oncorhynchus spp.). We created an interactive and searchable catalogue of evidence from predominantly primary literature using standardized systematic mapping protocols, with a focus on coding information to determine study reliability and relevance. Next, we synthesize the factor and mortality information to provide recommendations on the use of five major mortality risk factors that are linked to FRIM. Each factor (capture, handling, injury, water temperature, and predators) is scaled to a mortality risk to provide guidance on evaluating FRIM estimates. The recommendations from this work are focussed on addressing the current knowledge gaps and examining FRIM in broader physiological and ecological context. Ideas for future work include researching cumulative impacts, sub-lethal effects, drop-off mortality, and predation. We have chosen a fish-centric hybrid approach that focusses first on understanding factors that drive mortality, and then on mortality estimates. As such, this paper is not meant as the definitive guide on FRIM but a transparent, defensible, and rigorous evaluation of the primary evidence base for making future decisions about FRIM. Further guidance on how to use the information herein is part of an accompanying CSAS research document.

Key principles for understanding fish bycatch discard mortality

Article

Jan 2002
CAN J FISH AQUAT SCI

M.W. Davis

The mortality of discarded fish bycatch is an important issue in fisheries management and, because it is generally unmeasured, represents a large source of uncertainty in estimates of fishing mortality worldwide. Development of accurate measures of discard mortality requires fundamental knowledge, based on principles of bycatch stressor action, of why discarded fish die. To date, discard mortality studies in the field have focused on capture stressors. Recent laboratory discard experiments have demonstrated the significant role of environmental factors, size- and species-related sensitivity to stressors, and interactions of stressors, which increase mortality. In addition, delayed mortality was an important consideration in experimental design. The discard mortality problem is best addressed through a combination of laboratory investigation of classes of bycatch stressors to develop knowledge of key principles of bycatch stressor action and field experiments under realistic fishing conditions to verify our understanding and make predictions of discard mortality. This article makes the case for a broader ecological perspective on discard mortality that includes a suite of environmental and biological factors that may interact with capture stressors to increase stress and mortality.La mortalité des prises accessoires rejetées à l'eau est une question d'importance dans la gestion des pêches; parce qu'elle est rarement mesurée, elle représente une source considérable d'incertitude dans les estimations de la mortalité due à la pêche à l'échelle mondiale. L'élaboration de mesures précises de la mortalité des prises accessoires nécessite des connaissances fondamentales sur les causes de cette mortalité basées sur les modes d'action des facteurs de stress. À ce jour, les études se sont concentrées sur les stress reliés à la capture. Des études récentes en laboratoire ont souligné le rôle significatif des facteurs de l'environnement, de la sensibilité au stress spécifique à la taille et à l'espèce et des interactions entre les facteurs de stress, qui accroissent tous la mortalité. De plus, la mortalité retardée est un élément important du plan d'expériences. La meilleure façon d'aborder le problème de la mortalité des prises accessoires est par une combinaison d'études de laboratoire des différentes classes de facteurs de stress pour obtenir des connaissances sur les principes fondamentaux de leur mode d'action et par des expériences sur le terrain dans des conditions de pêche réalistes pour vérifier ces connaissances et faire des prédictions sur la moralité. Il faut donc utiliser dans l'étude de la mortalité des prises accessoires une perspective écologique élargie qui considère une série de facteurs environnementaux et biologiques qui peuvent interagir avec les facteurs de stress lors de la capture pour accroître le stress et la mortalité.[Traduit par la Rédaction]

The understudied and underappreciated role of predation in the mortality of fish released from fishing gears

Article

Mar 2013
FISH FISH

The assumption that animals released from fishing gears survive has frequently been scrutinized by researchers in recent years. Mortality estimates from these research efforts can be incorporated into management models to ensure the sustainability of fisheries and the conservation of threatened species. Post-release mortality estimates are typically made by holding the catch in a tank, pen or cage for short-term monitoring (e.g. 48 h). These estimates may be inaccurate in some cases because they fail to integrate the challenges of the wild environment. Most obvious among these challenges is predator evasion. Stress and injury from a capture experience can temporarily impair physiological capacity and alter behaviour in released animals, a period during which predation risk is likely elevated. In large-scale commercial fisheries, predators have adapted their behaviour to capitalize on impaired fishes being discarded, while in recreational catch-and-release fisheries, exercise and air exposure can similarly impede the capacity for released fish to evade opportunistic predators. Owing to the indirect and often cryptic nature of this source of mortality, very few studies have attempted to document it. A survey of the literature demonstrated that <2% of the papers in the combined realms of bycatch and catch-and-release have directly addressed or considered post-release predation. Future research should combine field telemetry and laboratory studies using both natural and simulated predation encounters and incorporate physiological and behavioural endpoints. Quite simply, predation is an understudied and underappreciated contributor to the mortality of animals released from fishing gears.

Key principles for understanding bycatch discard mortality

Article

Nov 2002
CAN J FISH AQUAT SCI

Michael W. Davis

The mortality of discarded fish bycatch is an important issue in fisheries management and, because it is generally unmeasured, represents a large source of uncertainty in estimates of fishing mortality worldwide. Development of accurate measures of discard mortality requires fundamental knowledge, based on principles of bycatch stressor action, of why discarded fish die. To date, discard mortality studies in the field have focused on capture stressors. Recent laboratory discard experiments have demonstrated the significant role of environmental factors, size- and species-related sensitivity to stressors, and interactions of stressors, which increase mortality. In addition, delayed mortality was an important consideration in experimental design. The discard mortality problem is best addressed through a combination of laboratory investigation of classes of bycatch stressors to develop knowledge of key principles of bycatch stressor action and field experiments under realistic fishing conditions to verify our understanding and make predictions of discard mortality. This article makes the case for a broader ecological perspective on discard mortality that includes a suite of environmental and biological factors that may interact with capture stressors to increase stress and mortality.

Postrelease Survival of Sublegal Southern Flounder Captured in a Commercial Gill-Net Fishery

Article

Full-text available

Jun 2011
N AM J FISH MANAGE

Discards from commercial fisheries may be subject to high rates of mortality that vary over time and space, contributing to inaccuracies in stock assessments. We present the results from a field experiment in the New River estuary, North Carolina, designed to estimate the postrelease survival of commercially gill‐netted, sublegal southern flounder Paralichthys lethostigma . Large, replicate field enclosures were used to monitor gill‐netted southern flounder for a 3‐d period after capture. The survival of observed discards showed significant variation among seasons. During fall and spring, overall survival was estimated to fall between 0.74 and 0.87, while during summer survival was estimated to fall between 0.22 and 0.30 and included fish that were dead when gill nets were retrieved. Logistic regression analysis was used to evaluate the relative effects of individual traits on the postrelease survival of southern flounder in the commercial gill‐net fishery. Model selection indicated that season and fish condition were the best characteristics with which to predict postrelease survival and that body size may also influence postrelease survival. Low seasonal estimates of the survival of discarded southern flounder suggest that management measures that mitigate poor discard survival will be most effective during the summer. Received November 11, 2010; accepted February 17, 2011

Mortality of Lingcod Towed in a Net as Related to FishLength, Seawater Temperature, and Air Exposure: ALaboratory Bycatch Study

Article

Nov 2002
N AM J FISH MANAGE

The mortality of discarded bycatch is a critical problem in the management of fisheries worldwide. Little is known about the key principles involved in the mortality of discarded bycatch. These principles are best elaborated under controlled conditions in the laboratory where the actions and interactions of stressors found in fishing practices can be investigated independently. The goal of this study was to investigate the principles involved in the mortality of lingcod Ophiodon elongatus by testing hypotheses concerning the factors that may control trawl bycatch mortality. Lingcod were towed in a net and exposed to increased seawater temperature and to air, two stressors that occur during the processes of trawl capture, retrieval through a thermocline, and landing on deck. Mortality occurred after exposure to more than 45 min in air, after exposure to 4 h towing in a net followed by more than 30 min in air, or after 4 h towing followed by exposure to seawater above 16.0°C for 30 min and air for 15 min. In treatments of equal stressor intensity, smaller fish (41–51 cm total length) had higher rates of mortality than larger fish (52–67 cm). The effects of net towing and air—as well as of towing, increased seawater temperature, and air—were additive. Lingcod bycatch mortality may be reduced by decreasing trawling times and exposure to increased seawater and air temperatures during warmer seasons or by restricting fisheries that produce bycatch to seasons of cooler temperatures. The sorting, handling, and release of bycatch on deck after capture may be conducted in a manner that would probably enhance survival if fish are released within 30 min of capture. Because smaller lingcod had higher rates of mortality, further information about the mortality rates of relevant size-classes of fish is needed to validate the assumptions of management rules for released, undersized bycatch that are designed to enhance recruitment.

The Effects of Scallop Dredge Fishing Practices on Physical, Behavioral, and Physiological Stress in Discarded Yellowtail Flounder, Windowpane, and Fourspot Flounder

Article

Full-text available

Feb 2021

The Atlantic sea scallop Placopecten magellanicus dredge fishery is one of the most lucrative commercial fishing industries in the northeastern United States, and fish bycatch can comprise up to~42% of the total catch. Benthic species , such as flatfish, are particularly susceptible to unintended capture in scallop dredge gear, and mitigating bycatch and associated mortality has been mandated a priority for fisheries management. Based on this management need, the present study evaluated the physical, physiological, and behavioral stress responses of Yellowtail Flounder Limanda ferruginea, Windowpane Scophthalmus aquosus, and Fourspot Flounder Paralichthys oblongus to capture in the scallop dredge fishery. More specifically, we used generalized additive models and linear regression models to assess the influence of various fishing practices, environmental conditions, and biological factors on injury condition, physiological parameters, and reflex indicators. Although these flatfish species appeared to be physically resilient to capture based on an observable injury assessment, dredge capture and handling factors proved stressful, with the degree of immediate mortality, physiological disturbances, and reflex impairment varying by species. While multiple factors influenced the degree of stress in these species, based on our results the reduction of tow duration and limiting air exposure/sorting duration would likely be the most effective strategies to mitigate the impact of scallop dredge fishing on these flatfish species.

Discards and Bycatch Research Program in Chile, 2015 (Programa de Investigación del Descarte y Captura de Pesca Incidental, 2015).

Technical Report

Full-text available

Jul 2016

This research program, considering a monitoring through fisheries observers aboard, have as aim to quantify and identify the causes of discards, to later develop and implement a mitigation plan in each demersal fishery.

FISH Out of WATER: How Much Air is Too Much?

Article

Full-text available

Sep 2015

Exposing fish to air following capture influences postrelease survival and behavior. Air exposure causes acute hypoxia and physical damage to the gill lamellae, resulting in physiological stress and physical damage that increases with air exposure duration. Air exposure duration is a relevant and easily quantified metric for both fishers and managers and can therefore provide a definitive benchmark for improving postrelease survival. Yet, fishers are rarely provided with specific recommendations other than simply to “minimize” air exposure. This is a subjective recommendation, potentially causing confusion and noncompliance. Here we discuss and summarize the literature regarding air exposure thresholds in both commercial and recreational fisheries, the factors influencing these thresholds, and identify knowledge gaps limiting our understanding of tolerance to air exposure in captured fish.

Stress induced by hooking, net towing, elevated sea water temperature and air in sablefish: lack of concordance between mortality and physiological measures of stress

Article

Jan 2001

Michael W. Davis

In a series of laboratory studies designed to simulate bycatch processes, sablefish Anoplopoma fimbria were either hooked for up to 24 h or towed in a net for 4 h and then subjected to an abrupt transfer to elevated sea water temperature and air. Mortality did not result from hooking or net towing followed by exposure to air, but increased for both capture methods as fish were exposed to elevated temperatures, reflecting the magnifying effect of elevated temperature on mortality. Hooking and exposure to air resulted in increased plasma cortisol and lactate concentrations, while the combination of hooking and exposure to elevated temperature and air resulted in increased lactate and potassium concentrations. In fish that were towed in a net and exposed to air, cortisol, lactate, potassium and sodium concen- trations increased, but when subjected to elevated temperature and air, no further increases occurred above the concentrations induced by net towing and air, suggesting a possible maximum of the physiological stress response. The results suggest that caution should be exercised when using physiological measures to quantify stress induced by capture and exposure to elevated temperature and air, that ultimately result in mortality, since the connections between physiological stress and mortality in bycatch processes remain to be fully understood.

Combining in-trawl video with observer coverage improves understanding of protected and vulnerable species by-catch in trawl fisheries

Article

Full-text available

Jul 2014

Assessments of incidental wildlife mortality resulting from fishing rarely account for unobserved by-catch. We assessed by-catch of protected and vulnerable wildlife species in an Australian trawl fishery by comparing in-trawl video footage with data collected by an on-board observer. Data were obtained from 44 commercial trawls with two different by-catch reduction devices (BRDs). Eighty-six individuals from six major taxa (dolphins, sharks, rays, sea snakes, turtles and sygnathids) were documented from video analysis, including the endangered scalloped hammerhead shark (Sphyrna lewini) and the critically endangered green sawfish (Pristis zijsron). On the basis of the 2008–2009 fishing effort of 4149 trawls and scaling from these results, we estimated the annual catch of protected and vulnerable species (± �1 s.e.) at 8109 ± �910 individuals. Only 34% of by-catch was expelled through the BRDs. Independent observer data for the 44 trawls showed that 77% of the landed by-catch from these taxa were dead when discarded. The results indicate that unaccounted by-catch in trawl fisheries can be substantial, and that current methods of recording by-catch on-board vessels are likely to underestimate total fishing mortality. We recommend gear modifications and their validation through dedicated observer coverage, combined with in-trawl video camera deployments to improve current approaches to by-catch mitigation.

Discard Mortality of Trawl-Caught Lingcod in Relation to Tow Duration and Time on Deck

Article

Full-text available

May 2003

The lingcod Ophiodon elongatus is a benthic marine fish commonly caught by groundfish trawlers and discarded due to low catch limits. Managers must account for the mortality of bycatch to assess population status accurately. Our objectives were to estimate the actual mortality of trawl-discarded lingcod (50–84 cm) and describe their physiological stress response to capture. We investigated three major factors of the trawling operation that may influence lingcod survival: tow duration, fish size, and the amount of time fish were on the deck of the vessel. Survival was monitored for 21 d and each surviving animal was then physically and physiologically evaluated. The results showed that regardless of the duration of the tow, lingcod survival was 100% for animals discarded immediately after the cod end was emptied on deck. All lingcod captured during a tow of average commercial duration demonstrated a maximal stress response, measured by plasma cortisol, glucose, and lactate concentrations. As expected, lingcod from an average duration tow showed decreased survival with increased time on deck, though still had 50% survival after 30 min. This study suggests that discard mortality of lingcod is determined mainly by on-deck sorting and can be minimized by releasing fish quickly upon capture. Accurate estimation of mortality rates for lingcod will depend on the documentation of normal fishing behavior and on-deck sorting procedures.

Fish Size and Exposure to Air: Potential Effects on Behavioral Impairment and Mortality Rates in Discarded Sablefish

Article

May 2004

Fisheries models often assume that discarded undersized fish and target species will survive and contribute to future recruitment and yield. If smaller fish are more susceptible to capture stressors than larger fish, then the assumption that smaller discards would contribute to recruitment may not be true. We tested the hypothesis that small sablefish Anoplopoma fimbria show more behavioral impairment and mortality than large fish when exposed to air (10–60 min) at various temperatures (10–18°C). Sablefish captured by trawl, longline, or trap are commonly exposed to these conditions during warmer seasons when brought up on deck and sorted. Two size-classes of fish (small: 32–49 cm total length (TL); large: 50–67 cm TL) were used in the experiments. Behavior was measured as upright orientation and startle responses to visual and mechanical stimuli 1, 2, 3, and 24 h after air exposure; mortality was measured through 7 d after air exposure. Small fish mortality increased as air time increased and was at higher levels than in large fish. Only 10 min of air exposure caused behavioral impairment in small and large fish, which could lead to increased predation on discarded fish. At 24 h after air exposure, normal behavior had not generally resumed and small fish had more behavioral impairment than large fish.

Stress induced by hooking, net towing, elevated sea water temperature and air in sablefish: Lack of concordance between mortality and physiological measures of stress

Article

Apr 2005
J FISH BIOL

In a series of laboratory studies designed to simulate bycatch processes, sablefish Anoplopoma fimbria were either hooked for up to 24 h or towed in a net for 4 h and then subjected to an abrupt transfer to elevated sea water temperature and air. Mortality did not result from hooking or net towing followed by exposure to air, but increased for both capture methods as fish were exposed to elevated temperatures, reflecting the magnifying effect of elevated temperature on mortality. Hooking and exposure to air resulted in increased plasma cortisol and lactate concentrations, while the combination of hooking and exposure to elevated temperature and air resulted in increased lactate and potassium oncentrations. In fish that were towed in a net and exposed to air, cortisol, lactate, potassium and sodium concentrations increased, but when subjected to elevated temperature and air, no further increases occurred above the concentrations induced by net towing and air, suggesting a possible maximum of the physiological stress response. The results suggest that caution should be exercised when using physiological measures to quantify stress induced by capture and exposure to elevated temperature and air, that ultimately result in mortality, since the connections between physiological stress and mortality in bycatch processes remain to be fully understood.

Reducing discard mortality in an estuarine trawl fishery

Article

Sep 2008
J EXP MAR BIOL ECOL

A purpose-built, water-filled sorting tray was compared against a conventional dry tray for its utility in reducing discard mortality across a range of conditions in an Australian estuarine penaeid-trawl fishery, including the limits of typical delays in starting sorting (2 vs. 15 min). During nine days of fishing, up to 10 replicate deployments were done for each sorting method and delay. Bycatches (44 389 teleosts comprising 15 species) were assessed for their immediate mortalities, before 1346 live individuals (10 species) were released (to simulate discarding) into replicate cages and monitored for their short-term mortalities over five days. Appropriate controls were included for the most abundant economically-important species, yellowfin bream, Acanthopagrus australis. Most trawled-and-discarded teleosts followed a pattern of minimal differences in immediate mortalities between sorting methods for the short delay, but generally fewer deaths in the water tray than in the conventional tray during the longer delay. However, owing to a dominant and slightly protracted influence of the trawling process, comparable rates of deaths were observed for caged fish irrespective of their post-capture treatment. Mixed-effects logistic models applied to four key species (A. australis; silver biddy, Gerres subfasciatus; southern herring, Herklotsichthys castelnaui; and Port Jackson glassfish, Ambassis jacksoniensis) revealed that in addition to the method and delay in sorting, the weights of total catch and jellyfish, salinity and the size of fish also had significant impacts on mortality. For the longer delay in sorting in the water tray, the influences of some of the other factors were negated so that total mortalities of three of the modelled species were reduced by almost one quarter. We conclude that while unaccounted fishing mortality can be reduced via changes to onboard sorting procedures, this approach should only be applied ancillary to efficient gear selectivity.

Temporary retention in cold water reduces post‐release behavioral impairment in angled Rainbow Trout ( Oncorhynchus mykiss )

Article

Full-text available

Nov 2021

The effectiveness of catch‐and‐release as a conservation practice assumes minimal impacts to released fish. In most cases, angling‐related stressors can be mitigated via changes to angler behavior that reduce fight duration, handling, and air exposure. In some cases, stressors may significantly impact the ability of fish to engage in normal swimming behavior upon release. In these scenarios, it may be beneficial for anglers to assist recovery or retain fish until they are adequately recovered. In our study, we investigated the effectiveness of two assisted‐recovery devices at facilitating behavioral recovery in angled Rainbow Trout (Oncorhynchus mykiss): 1) retention in a flow box or 2) retention in a water‐filled cooler. Additionally, we compared the effects of assisted recovery in surface water (24 ºC – 27 ºC) or cool water pumped from the hypolimnion (17 ºC – 19 ºC). From July to mid‐September of 2020, 169 fish were angled from five stocked lakes at Kenauk Nature (Montebello, QC). Trout were air exposed for 30 s, 15 s, or not at all (0 s) and held in a flow box or a water filled cooler for 3 minutes, while fish in a control group were immediately released. Tri‐axial acceleration and temperature biologgers were temporarily fixed around the trunk of the fish with Velcro® to observe post‐release swimming behavior for 10 minutes. Trout that were held in assisted recovery devices regained equilibrium significantly quicker compared to those that were immediately released, and fish that were held in 17 ºC – 19 ºC water regained equilibrium the most rapidly. In fish that were air exposed for 30 s, individuals that were held in recovery devices exhibited greater swimming activity compared to those that were immediately released. Our study demonstrates that for Rainbow Trout, assisted recovery devices can reduce equilibrium impairment, especially when water in the recovery devices is significantly cooler than the relatively warm surface water temperature. Global water temperatures are expected to rise as a result of anthropogenic climate change, and best practices for angling should be adapted to reflect increased thermal stressors for many game fish species. Ensuring fish are vigorous upon release is imperative for reducing post‐release mortality through predation or thermal stress.

Physiological effects of catch-and-release angling on freshwater drum (Aplodinotus grunniens)

Article

May 2021
FISH RES

Many catch-and-release angling events involve air exposure and exhaustive exercise that elicit a physiological stress response, and depending on a variety of factors, delayed mortality is a possible outcome. There have been ample studies in this area, however, significant gaps exist in the literature for species that are targeted by more specialized anglers, such as freshwater drum (Aplodinotus grunniens). We quantified physiological and reflex responses in freshwater drum following angling, across seasons. Once a fish was on the line, the fight duration and time exposed to air were varied to account for differences in angler skill level (fight time range: 5 s to 2 min; air exposure range: 20 s to 3 min). Location and severity of injury were determined, blood biopsies were taken to quantify physiological stress, and reflex impairment was assessed. Thirty-one percent of fish captured were deeply hooked in the esophagus tissue. Freshwater drum experienced a disruption in homeostasis as blood glucose, plasma cortisol, and plasma lactate increased significantly from baseline values following angling. Additionally, seasonal differences were observed for blood glucose and plasma cortisol as higher values were observed in the summer when compared to the spring. The ‘orientation’ reflex was the most frequently impaired (29 % of fish lacked this reflex), but impairment did not differ seasonally. Because freshwater drum have the largest latitudinal range of any North American freshwater fish and are being targeted more frequently by anglers as of late, it is important to fill this knowledge gap regarding their responses to angling events to develop best practices for anglers to promote conservation. The wide distribution of freshwater drum may also make them a candidate model species for addressing the convergence between assessing the impacts of catch-and-release angling and other environmental issues facing freshwater fishes, such as climate change.

Multispecies thermal dynamics of air-exposed ectothermic sharks and its implications for fisheries conservation

Article

Feb 2019
J EXP MAR BIOL ECOL

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.

Report of the ICES Workshop on Methods for Estimating Discard Survival 1 (WKMEDS 1)

Technical Report

Full-text available

Apr 2014

Bycatch in 36 and 40 mm PA Turkish twin rigged beam trawl codends

Article

Full-text available

Jul 2011
AFR J BIOTECHNOL

The Turkish twin rigged beam trawl which has two identical nets rigged side by side on the same beam targets mainly the Parapenaeus longirostris, although some bycatch fish species have also become target species. Thus, landings of the shrimp beam trawling fleet also include some commercially valuable fishes. Our study focused on the bycatch commercial species which are caught by the beam trawl fishery with nominal mesh sizes 36 and 40 mm PA (diamond) codend in the Sea of Marmara (Turkey) and also on the minimum landing size (MLS) established for Merluccius merluccius, Merlangius merlangus euxinus, Mullus surmuletus, Trachurus trachurus and Pomatomus saltatrix. Since there was no MLS value for Spicara smaris, the length at first maturity (LFM) was used for this species. Experiments were carried out onboard the commercial beam trawler. In 20 hauls, the average codend catch weight was 63.12 kg for 36 mm PA and 66.51 kg for 40 mm PA. On the other hand, for 36 mm PA, 83.5% of M. merluccius, 74.3% of M. merlangus euxinus, 29.7% of T. trachurus, 10.8% of P. saltatrix and 8.6% of M. surmuletus were below the MLS. For 40 mm PA, 88.9% of M. merlangus euxinus, 87.7% of M. merluccius, 42.5% of T. trachurus, 7.2% of P. saltatrix and 6.7% of M. surmuletus were below MLS. In addition, 7.5% of S. smaris were below length at first maturity (LFM) for 36 PA codends.

Looking beyond the mortality of bycatch: Sublethal effects of incidental capture on marine animals

Article

Full-text available

Mar 2014
BIOL CONSERV

There is a widely recognized need to understand and reduce the incidental effects of marine fishing on non-target animals. Previous research on marine bycatch has largely focused on simply quantifying mortality. However, much less is known about the organism-level sublethal effects, including the potential for behavioural alterations, physiological and energetic costs, and associated reductions in feeding, growth, or reproduction (i.e., fitness) which can occur undetected following escape or release from fishing gear. We reviewed the literature and found 133 marine bycatch papers that included sublethal endpoints such as physiological disturbance, behavioural impairment, injury, reflex impairment, and effects on reproduction, feeding, and growth for animals that survived a fisheries interaction. Of the 133 identified articles, 22 documented sublethal effects of capture using metrics directly related to fitness, life history, or population-level processes. Sublethal effects were classified as either short-term (e.g., acute stress response), which could lead to long-term or delayed sublethal outcomes (e.g., growth, reproduction), which are directly fitness-relevant and could have had population-level effects. We recommend further investigation into the effects of injury on fitness, and the effects of capture stress on reproduction. It is completely unknown whether sublethal effects can have significant consequences at the population- or ecosystem-level. To date, the potential for discards to suffer from sublethal fitness effects has been almost entirely ignored, and added knowledge on the topic could benefit both conservation and management.

A review of approaches to assess survival of released catch from Canadian large pelagic longline fisheries

Article

Full-text available

Jan 2011

Synoptic acoustic and trawl surveys of spring-spawning Atlantic cod in the Gulf of Maine cod spawning protection area

Article

Apr 2013
FISH RES

Repeated acoustic and trawl surveys were performed in the Gulf of Maine cod spawning protection area (GOMCSPA) to: (a) describe the spatial and temporal distribution of spring-spawning Atlantic cod (Gadus morhua); (b) estimate their abundance and biomass; and (c) evaluate precision of the survey methods. A fishing vessel equipped with 38- and 120-kHz split-beam echo sounders surveyed once monthly from dusk to dawn along ten parallel transects that covered a 80.8 km2 area during April–July 2011. During each survey, two bottom trawl vessels (one with a small mesh net and one with a large mesh net) each made ten tows in parallel behind the acoustic survey vessel. Cod abundance and biomass was derived from acoustic backscatter by a combination of methods: (1) species apportionment based on trawl catch vs. echo classification; (2) in situ vs. predicted target strength; (3) size of elementary distance sampling unit (EDSU) and statistical approach; and (4) with and without dead zone correction. The mean cod density based on echo classification and a 100-m EDSU resulted in a substantially lower coefficient of variation when the variance was estimated by geostatistics compared to any other method used. Based on echo classification, semivariogram modeling revealed that 67–77% of the variance in cod biomass density was explained by a spatial structural component at a range (correlation length) of 2.0–2.4 km. Density maps, produced by ordinary kriging, showed cod were relatively widespread in the survey area in May, but congregated at higher densities in areas adjacent to two elevated bathymetric features. Most cod converged to a single location in June, and were at a higher concentration compared to the highest densities observed in May. This congregation decreased in size and density in July. The survey estimates of cod biomass were 184–494 mt in May, 138–617 mt in June, and 39–135 mt in July. Based on echo classification, the biomass for the GOMCSPA, extrapolated from these survey estimates, were 260–466 mt in May, 196–513 mt in June, and 91–198 mt in July. These results provide some evidence that adult Atlantic cod in spawning condition congregated within the GOMCSPA during the seasonal fishing closure, and that the biomass being protected by the closure may have represented 4–5% of the GOM cod spawning stock biomass at the time of the study.

CONSIDERACIONES SOBRE LA PESCA INCIDENTAL PRODUCIDA POR LA ACTIVIDAD DE LA FLOTA ATUNERA DIRIGIDA A GRANDES PELÁGICOS

Article

INVESTIGACIÓN PESQUERA

Stress and Delayed Mortality Induced in Pacific Halibut by Exposure to Hooking, Net Towing, Elevated Seawater Temperature and Air: Implications for Management of Bycatch

Article

Nov 2001
N AM J FISH MANAGE

The extent of stress and eventual mortality in Pacific halibut Hippoglossus stenolepis that resulted from simulated capture by hooking or towing in a net, followed by abrupt exposure to warmer seawater temperature and air, were determined under laboratory conditions. Abrupt exposure to 16°C seawater and air after either method of capture increased capture-induced stress, with accompanying mortality of 33% for hooked fish and 78% for fish towed in a net. Moreover, these deaths occurred as long as 30 d after experimental treatment, suggesting that delayed mortality should be considered in any study of Pacific halibut bycatch mortality. Stress induced by hooking or towing in a net followed by air exposure was reflected in cessation of negative phototaxis and feeding, both of which were resumed after 5 d with no mortality occurring. The results of this study clearly show that seasonal increases in temperature associated with thermoclines and deck conditions have the potential for markedly increasing the mortality of Pacific halibut that might otherwise survive capture and release in colder seasons. Strategies for effective management of Pacific halibut bycatch need to include consideration of seasonal temperature increases and how this factor might increase mortality.

Linking “Sink or Swim” Indicators to Delayed Mortality in Red Snapper by Using a Condition Index

Article

Jan 2009

The ability of fish to submerge after discarding is often used as a proxy for survival, but this practice underestimates total discard mortality because delayed mortality is overlooked. Fishery managers need a way to link “sink or swim” indicators, or variables observed during capture and release, with delayed mortality rates. We conducted a cage study of red snapper Lutjanus campechanus off the coast of Texas to estimate delayed mortality rates and to find factors that could link immediate and delayed mortality. Immediate mortality (17%) was predicted by the interaction of depth and the difference in temperature between surface and bottom waters. Lactate levels were also significant predictors of immediate mortality in fish whose blood was tested. Delayed mortality (64%) was predicted primarily by a condition index consisting of the presence or absence of injuries, symptoms of barotrauma, and fish behaviors immediately after capture. Specific categories included bleeding, protruding intestines, everted stomach, exopthalmia, the presence or absence of flapping and gilling behaviors, and problems with cage submergence. The majority of fatalities occurred within 24 h after fish were placed in the cages. Our mortality estimates indicate that red snapper discard mortality was significantly underestimated in the 2005 stock assessment for red snapper. The use of indices that relate the condition of an individual fish at capture to its probability of delayed mortality is an excellent method for linking immediate and delayed mortality and will likely be applicable to many species that are subject to catch-and-release fishing.

Estimating collateral mortality from towed fishing gear

Article

Aug 2006
FISH FISH

More than 50% of the world's total marine catch (approximately 81 million tonnes) is harvested using towed fishing gears (i.e. Danish seines, dredges and otter and beam trawls). As for all methods, the total fishing mortality of these gears comprises the reported (landed) and unreported catch and other unaccounted, collateral deaths due to (i) avoiding, (ii) escaping, (iii) dropping out of the gear during fishing, (iv) discarding from the vessel, (v) ghost fishing of lost gear, (vi) habitat destruction or subsequent (vii) predation and (viii) infection from any of the above. The inherent poor selectivity of many towed gears, combined with their broad spatial deployment, means that there is considerable potential for cumulative effects of (i)–(viii) listed above on total fishing mortality, and subsequent wide-scale negative impacts on stocks of important species. In this paper, we develop a strategy for minimizing this unwanted exploitation by reviewing all the primary literature studies that have estimated collateral, unaccounted fishing mortalities and identifying the key causal factors. We located more than 80 relevant published studies (between 1890 and early 2006) that quantified the mortalities of more than 120 species of escaping (26 papers) or discarded (62 papers) bivalves, cephalopods, crustaceans, echinoderms, elasmobranches, reptiles, teleosts and miscellaneous organisms. Seven of these studies also included the estimates of mortalities caused by dropping out of gears, predation and infection [(iii), (vii) and (viii) listed above]. Owing to several key biological (physiology, size and catch volume and composition), environmental (temperature, hypoxia, sea state and availability of light) and technical (gear design, tow duration and speed) factors, catch-and-escape or catch-and-discarding mechanisms were identified to evoke cumulative negative effects on the health of most organisms. We propose that because the mortalities of discards typically are much greater than escapees, the primary focus of efforts to mitigate unaccounted fishing mortalities should concentrate on the rapid, passive, size and species selection of non-target organisms from the anterior sections of towed gears during fishing. Once maximum selection has been achieved and demonstrated to cause few mortalities, efforts should be made to modify other operational and/or post-capture handling procedures that address the key causal factors listed above.

Behaviour impairment in captured and released sablefish: Ecological consequences and possible substitute measures for delayed discard mortality

Article

Jan 2005
J FISH BIOL

Michael W. Davis

Sablefish Anoplopoma fimbria aged 1+ and 2+ years were towed for 4 h in a net, transferred to air for either 15 or 30 min, and then held in tanks for up to 35 days for observation of physical injury, immediate mortality, behaviour impairment, delayed mortality and total mortality. Behaviour was impaired for at least 3 h and returned to normal levels by 24 h after stress induction. Behaviour impairment was correlated with delayed mortality in 2+ year fish but not in 1+ year fish which showed greater variation in stress responses. The results of this study and a review of past discard and escapee studies showed that substitute measures for delayed mortality in the field should include physical injury and behaviour impairment. These two measures integrate the effects of capture-related stressors which can produce and magnify physical and physiological injury, resulting in changes in fish condition and delayed mortality.

Assessing the factors influencing discard mortality of demersal fishes using a semi-quantitative indicator of survival potential

Article

Dec 2010
FISH RES

Understanding the factors affecting the likelihood that discarded fish will die can contribute to better management of resources by enhancing the potential for successful live release and by improving the estimation of otherwise unaccounted fishing mortality. Semi-quantitative measures of individual fish vitality or physical condition, obtained by at-sea observers aboard commercial fishing vessels, are often used as an indicator of survival potential for discarded fish. The present study and previous ones have shown that these measures relate well to eventual survival. However, observer subjectivity in fish vitality scoring can affect the precision and accuracy of inferences drawn from an analysis of the observations. Here we propose the use of a mixed-effects multinomial proportional-odds model, which is appropriate for modelling ordinal vitality data and is a useful approach for addressing observer scoring subjectivity. This model was used to analyse data collected for eleven fish taxa captured by four gear types. The effect of eight factors previously shown to affect discard survival was evaluated. The gear type used and amount of time that fish spent on deck prior to discarding most strongly and consistently affected the distribution of fish among vitality levels. Sea surface and air temperatures, and fish body size, were also important factors for a number of taxa, while other factors such as the depth fished, catch size and fishing activity duration were important only for certain taxa. A random effect in the model, used to account for observer subjectivity, was significant for most taxa and fisheries. Failure to account for this effect could affect both the precision and accuracy of inferences on the survival potential of discarded fish.

Bycatch quotas in the Gulf of Mexico shrimp trawl fishery: Can they work?

Article

Full-text available

Jun 2004

Sandra L. Diamond

Bycatch of unwanted, prohibited, or protected species is a problem in most commercial fisheries. Trawl fisheries are particularly prone to bycatch problems because trawls are not species-selective. In this paper, I review the history of finfish bycatch research in the Gulf of Mexico shrimp trawl fishery and explore the use of quotas to reduce finfish bycatch by examining four fisheries that currently use bycatch quotas: (1) the arrow squid trawl fishery of New Zealand, which uses fleet bycatch quotas for sea lion bycatch, (2) the Alaskan groundfish trawl fisheries, which use fleet quotas under a vessel incentive program for prohibited species, (3) the groundfish trawl fishery of British Columbia, Canada which uses individual vessel bycatch quotas for prohibited species, and (4) the multi-species trawl fisheries of New Zealand, which use catch balancing, or individual transferable quotas, for most commercially landed species. Based on the bycatch quota experiences in these fisheries, elements of successful bycatch quota programs include: (1) individual accountability, in the form of individual or cooperative bycatch quotas, rather than fleet quotas, (2) 100% observer coverage, (3) relatively small, manageable fleets, (4) limited landing ports that can be easily monitored, particularly if observer coverage is incomplete, (5) reliable enforcement, (6) penalties that are true disincentives, and (7) some flexibility in the system for fishermen to have alternatives to manage their bycatch. The Gulf of Mexico shrimp trawl fishery, with an estimated 20,000 licensed boats, is currently too large for individual bycatch quotas to be practical, although individual or cooperative bycatch quotas would be excellent strategies for reducing the bycatch of a smaller fleet. Mobile closed areas might be beneficial for reducing the bycatch of particular species, but these short-term closures would require real-time monitoring of bycatch rates and vessel monitoring systems on all vessels. However, under any management regime, incentives and/or rigorously enforced disincentives are the key to successful bycatch reduction.

Long-term impact of incidental catches by tuna longlines: the black escolar (Lepidocybium flavobrunneum) of the southwestern Atlantic Ocean

Article

Nov 2002
FISH RES

We analyze intra and inter-annual harvesting patterns of the black escolar Lepidocybium flavobrunneum (Gempylidae), an important component of the incidental catch of the Uruguayan tuna fleet (UTF) at the southwestern Atlantic Ocean (SAO), based on daily information of catch, fishing effort and individual weight of all the specimens caught during 16 years (1981–1996). The analysis also compares the activities of two fishing fleets that operated in two different periods of fishery development: category A, which comprises Japanese vessels that operated between 1981 and 1991, and category B, consisting of American and Spanish vessels that operated between 1992 and 1996. The relative representation of the total incidental catch significantly increased during the 16-year period of activity of the UTF, reaching 43% of the total catch in 1995. A recurrent seasonal pattern in fishing effort, catch and catch per unit of effort (CPUE) was observed, peaking in austral winter and spring. The daily number of hooks and total catch were significantly higher for category A, which exerted 2.7 times higher number of hooks and obtained catches 3.33 times higher than category B. Differing with the above trends, mean daily CPUE of a category B vessel was 16% higher than category A, which can be attributed to the increase of fishing power. The mean individual weight decreased almost 40% in 15 years, i.e., from 23.2 kg in 1982 to 14.1 kg in 1996, suggesting overexploitation risks of this incidental species. The effect of increasing fishing power and the effectiveness of management measures for large pelagics at the SAO are discussed.

Trawl capture of Port Jackson sharks, Heterodontus portusjacksoni, and gummy sharks, Mustelus antarcticus, in a controlled setting: Effects of tow duration, air exposure and crowding

Article

Dec 2010
FISH RES

Delayed effects of fisheries capture on the physiology and condition of sharks are poorly understood, but information on the post-release fate of sharks that have been incidentally captured, handled, and released is important to elaborate effective fisheries management measures for by-catch shark species. By-catch is often substantial during commercial trawling operations, and fish are exposed to a multitude of different stressful stimuli during trawl capture. We subjected Port Jackson sharks, Heterodontus portusjacksoni, and gummy sharks, Mustelus antarcticus, to trawl capture in a controlled setting to investigate effects of tow duration, exposure to air, and crowding in the codend, and monitored their condition via repeated blood sampling during a 72-h recovery period subsequent to the capture event. Port Jackson sharks experienced a low degree of physiological disturbance in response to our capture treatments and no mortality was observed during or after any experiments. Conversely, homeostatic balance of gummy sharks was severely disrupted by trawl capture, and immediate and delayed mortality was substantial (up to 87%) during some experiments. Moribund gummy sharks showed significantly increased blood lactate (>15 mmol/L) and potassium levels (>8 mmol/L) compared with surviving sharks, but these differences did not become evident until 6–12 h after the capture event. There was no strong evidence for an increase in physiological disturbance with increasing tow duration in either species. Extended periods of air exposure (>10 min) following a capture event may lead to additional physiological stress, but simulated crowding as performed in the present study did not result in increased physiological stress compared with trawl capture of individual animals. The results of this study suggest that trawl capture may lead to significant immediate and delayed mortality in gummy sharks, and that extended air exposure on deck may further exacerbate the deleterious effects of capture stress.

By-Catch: Problems and Solutions

Article

Full-text available

Dec 2000
MAR POLLUT BULL

By-catch is one of the most significant issues affecting fisheries management today. Incidental mortality of species which are long-lived and have low reproductive rates is a conservation problem affecting marine mammals, sea birds, sea turtles, sharks and other groups. By-catches can affect biodiversity through impacts on top predators, the removal of individuals from many species, or by elimination of prey. The by-catch issue is also one of waste; the millions of tons of protein dumped in the ocean, and the waste of animal lives is often condemned on moral grounds. For the economist, it generates additional costs without affecting the revenues, and may hinder profitability. For the fishers, it causes conflicts among fisheries, it gives fishers a bad public image, generates regulations and limitations on the use of resources, and frequently has negative effects on the resources harvested through the mortality of juvenile and undersized individuals of the target species before they reach their optimal size from the point of view of future yield.Several examples of major by-catch issues are described, focusing also on the solutions to the problems which have been developed by scientists, fisheries managers and members of the fishing industry itself. By-catch is an extremely complex set of scientific issues, not only an economic, political, or moral one. Although only a few fisheries include by-catches of the target species in their stock assessment (e.g. Pacific halibut), it is clear that by-catch management will be an integral part of most future ecosystem management schemes. These considerations, together with the introduction of environmental variability and a better handling of scientific uncertainty, should lead to more intelligent ways to harvest our resources.

Analysis of the factors affecting the discard fate for trawl fishery

Thesis

Full-text available

Jun 2018

Emrah Şimşek

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.

Survival of discarded plaice ( Pleuronectes platessa ) from Norway lobster ( Nephrops norvegicus ) otter-trawl fishery

Article

Full-text available

Mar 2019

The introduction of landing obligations in the European Union common fisheries policy, has increased the focus on discard survival. Since species with scientifically proven high survival rates may be exempted from the landing obligations, the economic significance for the fishing industry is large. Landing obligations include individuals below the minimum conservation reference size (MCRS), which are not allowed to be sold for human consumption. The Norway lobster (Nephrops norvegicus) fishery is a high value fishery, but with a substantial amount of bycatch of plaice (Pleuronectes platessa) below the MCRS. In the present study, observations were made on the short‐term survival of plaice at or below the MCRS, discarded from a small otter board trawler targeting Nephrops in Skagerrak (ICES 3a). The average short‐term survival of plaice was 15% at haul level, ranging from 0% to 39%, after 10 days of captive observation. Survival significantly decreased with time on deck and the retention of debris in the codend (p < 0.0001), while survival was not correlated to size. Vitality assessments, using a combined reflex impairment and injury score, were tested as predictor of survival and were significantly associated to survival (p < 0.0001) both for individual fish and when grouped by hauls. Seabird predation behaviour was assessed and it was estimated that seabirds predated or pursued 85% of discarded plaice below the MCRS.

Effect of the salt-box catch-bycatch separation procedure, as used by the Texas shrimp industry, on short-term survival of bycatch

Article

Jul 2001
FISH B-NOAA

Experiments were conducted to determine the effect of the salt-box catch-bycatch separation procedure, as used by the Texas shrimp industry, on short-term survival of bycatch. Bioassays were conducted on five economically important bycatch species: spotted seatrout (Cynoscion nebulosus); red drum (Sciaenops ocellatus); Atlantic croaker (Micropogonias undulatus); southern flounder (Paralichthyes lethostigma); and blue crab (Callinectes sapidus). Red drum were most affected by hypersalinity, requiring 17 minutes exposure to a 70 parts per thousand salt water solution to kill 50% of the test specimens within 48 hours. For samples collected from commercial boats and Texas Parks and Wildlife (TPW) trawl samples, we found that neither initial nor final percent survival was significantly different for bycatch removed with or without the aid of a salt-box, Bycatch mortality was high regardless of the method used to separate bycatch from the target catch, At the conclusion of catch separation, bycatch survival averaged 76% (+/- 22%) for commercial samples and 48% (+/- 40%) for TPW trawl samples separated with salt-boxes. Survival at the conclusion of catch separation without a salt-box averaged 56% (+/- 35%) for commercial samples and 43% (+/- 39%) for TPW trawl samples. Bycatch survival 21-27 h after catch separation averaged 13% (+/-6%) for commercial samples and 5% (+/-9%) for TPW trawl samples separated with salt-boxes and 34% (+/- 29%) for commercial samples and 10% (+/- 19%) in TPW trawl samples separated without a salt-box. Mortality rates (AT) for bycatch separated with a salt-box averaged 0.08 (+/-0.03) for commercial samples and 0.10 (+/-0.04) for TPW trawl samples. For bycatch separated without the salt-box, M averaged 0.48 (+/-1.23) for commercial samples and 0.10 (+/-0.05) for TPW trawl samples. Results of an exploratory analysis with stepwise multiple regression suggested that final percent survival of bycatch was most affected by trawling time. The salt-box had little or no effect on bycatch survival; therefore, regulating the use of salt-boxes in shrimp trawling operations is not necessary.

Mortality of fish escaping trawl gears

Article

Full-text available

Jan 2005

Petri Suuronen

Post-capture survival of Atlantic wolffish (Anarhichas lupus) captured by bottom otter trawl: Can live release programs contribute to the recovery of species at risk?

Article

Jan 2013
FISH RES

In 2003, the Atlantic wolffish (Anarhichas lupus), spotted wolffish (A. minor), and northern wolffish (A. denticulatus) were placed on Schedule 1 of Canada's Species at Risk Act which afforded them protection against harm. Consequently, it is mandatory to release both northern and spotted wolffish and it has been recommended that live-release protocols also apply to Atlantic wolffish. Catches in trawls comprise a significant threat to recovery of all three wolffish species and the Grand Bank yellowtail flounder (Limanda ferruginea) otter trawl fishery overlaps the most persistent high concentrations of Atlantic wolffish in the western North Atlantic. As a result, the trawl fishery initiated a voluntary live-release program. The current study investigated the post-capture survival of Atlantic wolffish captured incidentally in the Grand Bank yellowtail flounder otter trawl fishery. Short-term survival was monitored for wolffish placed in holding tanks onboard commercial vessels as well as wolffish returned to the ocean floor in cages. High (92–100%) post-capture survival was demonstrated in Atlantic wolffish following net entrainment in commercial tows up to 2.5 h, haul back through a thermocline (range, 5.8 °C), and exposure to 5–13 °C air temperatures for up to 2 h. High post-capture survival and similarities among all three species of wolffish with regard to morphology, physiology, post-capture activity levels, and tag returns in previous studies suggest live-release programs will help to rebuild populations of all three wolffish species. From a conservation perspective, release of wolffish can only be effective if it does not interfere with reproduction. Uncertainties with regard to the reproductive success of egg guarding male wolffish when returned to the ocean are discussed.

Mortality of brown-shrimp discards from the beam trawl fishery in the Tagus estuary, Portugal

Article

Sep 2003
FISH RES

Beam trawling results in large amounts of discards. Discards mortality may be influenced by some of the procedures aboard fishing vessels. In the present study, the influence of temperature of the sorting containers, of sorting time and of haul duration on the mortality of brown-shrimp discards from the beam trawl fishery in the Tagus estuary was evaluated. Experiments were conducted in the summer and in the winter of 2000, simulating on-board procedures, in different conditions. The sorting containers were either wooden, plastic or metallic, dark or light-coloured, and two sorting times (5 and 10 min) and three haul durations (10, 20 and 30 min) were considered. The light-coloured wooden and plastic containers presented the lowest temperatures, whereas the highest one was measured on the dark metallic container. For temperatures between 10 and 20 °C, mortality was nil; for values higher than 20 °C, mortality was high, reaching 96% in the temperature interval 40–50 °C. Discards mortality was similar for both sorting times considered. The mortality of discards increased with longer haul duration; for 10 min, mean mortality was 7%, whereas for 30 min was 75%. The use of light-coloured wooden or plastic sorting containers in summer and the avoidance of fishing activities at the hottest times of day in this season are suggested as management measures to minimise discards mortality in beam trawl fisheries.

Results of an Experimental Shrimp Fishery in Chaleur Bay, Southern Gulf of St. Lawrence

Article

Aug 1999

Five surveys of coastal shrimp abundance and distribution were conducted aboard a commercial shrimp trawler between 25 August and 4 November 1997 to evaluate the potential for a commercial shrimp fishery in Chaleur Bay, southern Gulf of St. Lawrence. The net was equipped with a fish exclusion grate (25-mm bar spacing) to reduce fish bycatch. The initial target species was sevenspine bay shrimp Crangon septemspinosa, but very few were captured in the depths fished (20-82 m). The principal shrimp species captured were Aesop shrimp Pandalus montagui and Arctic argid Argis dentata. The catch rates of shrimp were too low to support a commercial shrimp fishery in Chaleur Bay. Average catch rates for Aesop shrimp ranged between 0.5 and 3.2 kg/h (whole animals, wet weight), and catch rates for Arctic argid ranged between 0.5 and 9.3 kg/h. Bycatch of fish was low (usually < 10 kg/h) from late August to October but were excessive during early November when an average of 102 kg/h of Atlantic herring Clupea harengus and rainbow smelt Osmerus mordax were caught.

Estimating Handling Mortality Due to Air Exposure: Development and Application of Thermal Models for the Bering Sea Snow Crab Fishery

Article

Mar 2005

Peter G. van Tamelen

The fishery for snow crabs Chionoecetes opilio in Alaska occurs during the winter, and handling mortality may be high due to cold-air exposure. Heat budget models that include convection, evaporation, long-wave radiation, and solar radiation were developed for snow crabs. Model performance was evaluated by comparing observed and predicted temperatures of live crabs exposed to cold air. The model performed well, predicting temperatures of the body, legs, and eyes within 1.5°C. Legs and eyes cooled faster than the body and may be more susceptible to cold-air exposure. Weather variables were ranked in the following order of importance: (1) air temperature, (2) solar radiation, (3) wind speed, (4) humidity, and (5) cloud cover. Clear, cold, breezy nights are the most detrimental conditions for crabs. Hourly weather records from a site near the fishing grounds were used in conjunction with the thermal model to estimate cooling rates for crabs every hour during actual and hypothetical seasons. The probability of damage for various cooling rates was estimated based on previously published laboratory data. Discard handling damage rates were highly variable, ranging from 0% to 30% over 21 actual fishing seasons. Damage rates for hypothetical seasons that varied in length, start day, and daily fishing hours were calculated. Damage rates were reduced by delaying the start day (15 January) until 1 March as well as by limiting fishing time to daylight hours. Combining a later starting day with limited fishing hours resulted in 90% of the hypothetical seasons having damage rates of 10% or less. Generally, longer seasons had lower damage rates, especially when fishing hours were limited. Although developed for cold-weather Alaska fisheries, this approach can easily be adapted to other fisheries where handling mortality due to temperature changes during capture is a concern.

The Nova Scotia GPI Fisheries and Marine Environment Accounts – a Preliminary Set of Ecological, Socioeconomic and Institutional Indicators for Nova Scotia's Fisheries and Marine Environment

Article

Full-text available

Jan 2002

The role of temperature in the capture and release of fish

Article

Sep 2011
FISH FISH

We searched major electronic databases to identify peer-reviewed literature investigating the role of temperature on the stress response and mortality of captured and released fish. We identified 83 studies that fit these criteria, the majority of which were conducted in North America (81%) on freshwater fish (76%) in the orders Perciformes (52%) and Salmoniformes (28%). We found that hook-and-line fisheries (65% of all studies) were more commonly studied than all net fisheries combined (24%). Despite the wide recognition for many species that high water temperatures exacerbate the effects of capture on released fish, this review is the first to quantitatively investigate this problem, finding that warming contributed to both mortality and indices of stress in 70% of articles that measured each of those endpoints. However, more than half (58%) of the articles failed to place the experimental temperatures into a biological context, therefore limiting their broad applicability to management. Integration of survival and sublethal effects to investigate mechanisms of fish mortality was relatively rare (28%). Collectively, the results suggest that capture–release mortality increases at temperatures within, rather than above, species-specific thermal preferenda. We illustrate how knowledge of ecologically relevant high temperatures in the capture and release of fish can be incorporated into management, which will become increasingly important as climate change exerts additional pressure on fish and fisheries.

Bycatch rates and initial mortality of paddlefish in a commercial gillnet fishery

Article

Mar 2006
FISH RES

Tennessee is one of seven states in the U.S. that allows commercial fishing for paddlefish, Polyodon spathula. Although there is a small market for the flesh, most fishers target paddlefish for their valuable roe, which currently brings as much as US$143/kg wholesale. We deployed experimental monofilament and multifilament gillnets in Kentucky Lake, Tennessee-Kentucky, and accompanied commercial gillnet fishers during the 2003–2004 and 2004–2005 commercial fishing seasons (November 15 to April 23) to estimate the bycatch of sublegal (<864 mm eye-fork length) paddlefish, legal males, and legal, but immature, females. Variation in initial mortality (i.e., dead in the nets) was modeled as a function of mesh size, fish length, water temperature, soak time, and twine type using multiple logistic regression. The bycatch rate of sublegal fish in the commercial catch was 60%. Mature females represented only 8% of the catch; thus, the bycatch rate was 92% for fishers targeting egg-laden fish. Most (71%) of the paddlefish were dead in the nets when water temperatures exceeded 17 °C. Mesh size and fish length were not significant (P ≥ 0.098) predictors of initial mortality. The probability of initial mortality was significantly (P ≤ 0.004) and directly related to soak time and water temperature and fish were more likely to be dead in monofilament nets than multifilament nets. The results of this research prompted the state regulatory authority to end the commercial season 8 days sooner (on April 15 each year) to avoid warm water temperatures; however, a proposed ban on monofilament netting met with stiff opposition from commercial fishing interests and the ban was not enacted.

Evaluation of the interactive effects of air exposure and water temperature on the condition and survival of angled and released fish

Article

Sep 2007
FISH RES

At present, there is a reasonable understanding of the independent effects of catch-and-release (C&R) angling stressors, such as air exposure and water temperature, on endpoints such as physiological disturbance, behavioural impairment and mortality. However, little is known about the multiplicative or interactive nature of these different C&R stressors. This study used bluegill (Lepomis macrochirus) as a model to evaluate the combined effects of water temperature and air exposure on fish behaviour, equilibrium status and short-term mortality following C&R. Experiments were replicated over 3 days with different ambient water temperatures (18.3, 22.8 and 27.4 °C). On each day, fish were captured by standard angling techniques, exposed to a range of air exposure durations (0, 30, 60, 120, 240, 480 and 960 s), and subsequently monitored for behavioural changes (within the first 300 s) and short-term (48 h) delayed mortality. Additional fish were captured by seine net for use as controls. There was an interactive effect of temperature and air exposure, whereby fish exposed to the highest temperature and longer air exposure durations lost equilibrium more often and had depressed ventilation rates relative to fish exposed to minimal air exposure and the lowest temperature. Immediate mortality at the lowest temperatures was negligible. However, significant delayed mortality (up to 80%) was noted at the highest water temperature (27.4 °C) in fish exposed to the three longest air exposure groups. In addition, at 27.4 °C, mortality among fish exposed to 480 and 960 s occurred at a faster rate than in any other treatment group. These results indicate that at low to moderate water temperatures, extended air exposure for bluegill may result in little mortality. However, at high water temperatures, short-term mortality (within 48 h) can be substantial, especially for fish that experience extended air exposure durations. Anglers and managers must recognize that C&R stressors can interact to have more dire consequences than when applied independently.