Article

Capture-Related Stressors Impair Immune System Function in Sablefish

January 2006
Transactions of the American Fisheries Society 135(1):129-138

DOI:10.1577/T04-198.1

Authors:

Michael W. Davis

NOAA Fisheries

Carl B Schreck

Oregon State University

The sablefish Anoplopoma fimbria is a valuable North Pacific Ocean species that, when not targeted in various commercial fisheries, is often a part of discarded bycatch. Predictions of the survival of discarded fish are dependent on understanding how a fish responds to stressful conditions. Our objective was to describe the immunological health of sablefish exposed to capture stressors. In laboratory experiments designed to simulate the capture process, we subjected sablefish to various stressors that might influence survival: Towing in a net, hooking, elevated seawater and air temperatures, and air exposure time. After stress was imposed, the in vitro mitogen-stimulated proliferation of sablefish leukocytes was used to evaluate the function of the immune system in an assay we validated for this species. The results demonstrated that regardless of fishing gear type, exposure to elevated seawater temperature, or time in air, the leukocytes from stressed sablefish exhibited significantly diminished proliferative responses to the T-cell mitogen, concanavalin A, or the B-cell mitogen, lipopolysaccharide. There was no difference in the immunological responses associated with seawater or air temperature. The duration and severity of the capture stressors applied in our study were harsh enough to induce significantly elevated levels of plasma cortisol and glucose, but there was no difference in the magnitude of levels among stressor treatments. These data suggest that immunological suppression occurs in sablefish subjected to capture-related stressors. The functional impairment of the immune system after capture presents a potential reason why delayed mortality is possible in discarded sablefish. Further studies are needed to determine whether delayed mortality in discarded sablefish can be caused by increased susceptibility to infectious agents resulting from stressor-mediated immunosuppression.

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.

Factors Affecting Catch and Release (CAR) Mortality in Fish: Insight into CAR Mortality in Red Snapper and the Influence of Catastrophic Decompression

Chapter

Full-text available

Jan 2007

Jodie L Rummer

The red snapper Lutjanus campechanus fishery is arguably one of the most important in the North American Gulf of Mexico, but habitat destruction, cli-mate change, and serial overfishing has resulted in significant population declines in red snapper and other high-profile fisheries species. The red snapper fishery may be one of the best examples where management strategies that promote catch and release (CAR) have failed. Populations have not recovered despite CAR management strate-gies, likely because CAR mortality is high; however, the basis for CAR mortality is un-clear. Numerous studies associated with fishing-induced mortality were reviewed in an attempt to make generalizations as to how red snapper and other high-profile fisheries species respond to CAR. A framework for understanding CAR mortality in red snapper and other species was constructed based on four pillars: retrieval conditions, species and size relationships, handling, and release conditions. Each of these fishing factors was examined as to relative impact toward CAR. A predictive model was generated from all available data on CAR mortality. For a deep-water fish like the red snapper, the underlying problem is directly related to capture depth, particularly injuries related to rapid swim bladder (SB) overinflation and catastrophic decompression syndrome (CDS). If not immediately lethal, depth-related injuries may have long term effects on growth and immune function that could go unnoticed and are unaccounted for in traditional field studies; all other fishing factors will only intensify this baseline impair-ment. Management plans are typically built under the assumption that CAR mortality is below 20%, but it is widely accepted that this is a gross underestimate. Modeling from this review suggests that, in red snapper, mortality may be as low as 20% but only if fish are caught between 0 and 20 m depths. This is not the case, and CAR mortality may reach 100% if fish are retrieved from deeper than 110 m. Current CAR manage-ment strategies are ineffective, and not enough information exists to impose maximum fishing depths. Given these limitations, a logical approach would be to restrict particu-lar areas such that fish populations can be protected from all fishing and CAR activ-ity, therefore protecting age, size, and sex classes and ratios. For fish species like red snapper, where overfishing is widespread and CAR mortality is high, or other species where CAR is unclear and a thorough investigation as to depth-related CAR mortality has not been performed, strategies based on space (i.e., marine protected areas and no-take reserves), rather than time or numbers (i.e., season closures, size limits, bag limits, etc.), have the greatest potential for overall conservation and sustainability and should be strongly considered.

From transcriptome to biological function: environmental stress in an ectothermic vertebrate, the coral reef fish Pomacentrus moluccensis

Article

Oct 2007

Background Our understanding of the importance of transcriptional regulation for biological function is continuously improving. We still know, however, comparatively little about how environmentally induced stress affects gene expression in vertebrates, and the consistency of transcriptional stress responses to different types of environmental stress. In this study, we used a multi-stressor approach to identify components of a common stress response as well as components unique to different types of environmental stress. We exposed individuals of the coral reef fish Pomacentrus moluccensis to hypoxic, hyposmotic, cold and heat shock and measured the responses of approximately 16,000 genes in liver. We also compared winter and summer responses to heat shock to examine the capacity for such responses to vary with acclimation to different ambient temperatures.ResultsWe identified a series of gene functions that were involved in all stress responses examined here, suggesting some common effects of stress on biological function. These common responses were achieved by the regulation of largely independent sets of genes; the responses of individual genes varied greatly across different stress types. In response to heat exposure over five days, a total of 324 gene loci were differentially expressed. Many heat-responsive genes had functions associated with protein turnover, metabolism, and the response to oxidative stress. We were also able to identify groups of co-regulated genes, the genes within which shared similar functions.Conclusion This is the first environmental genomic study to measure gene regulation in response to different environmental stressors in a natural population of a warm-adapted ectothermic vertebrate. We have shown that different types of environmental stress induce expression changes in genes with similar gene functions, but that the responses of individual genes vary between stress types. The functions of heat-responsive genes suggest that prolonged heat exposure leads to oxidative stress and protein damage, a challenge of the immune system, and the re-allocation of energy sources. This study hence offers insight into the effects of environmental stress on biological function and sheds light on the expected sensitivity of coral reef fishes to elevated temperatures in the future.

Resilience of Pink Salmon and Chum Salmon to Simulated Fisheries Capture Stress Incurred upon Arrival at Spawning Grounds

Article

Oct 2012

We compared exhaustion‐related physiological stress and physical injury as contributors to fish condition, longevity, and egg retention in two Pacific salmon species after their arrival at spawning areas. Adult female Pink Salmon Oncorhynchus gorbuscha and Chum Salmon O. keta were exposed to six experimental capture treatments that represented different levels of exhaustive exercise, air exposure, and injury. After we evaluated its reflex impairment and obtained a blood sample, each fish was released into its natal spawning channel with an external tag and later retrieved postmortem to evaluate spawning success via examining egg retention. Reflex impairment, plasma lactate, chloride, potassium, and osmolality varied among treatments, with differences generally driven by the length of exposure to capture stress, which included exhaustive exercise and air exposure. However, overall prespawn mortality was negligible (about 5%) and consistent across treatments for both species. We hypothesize that Pink and Chum Salmon are resilient to capture‐related exhaustion upon reaching spawning areas because of a combination of low water temperature (about 12°C in this study) and a physiological shift towards increased use of anaerobic pathways during their final weeks of life. The capture and release of fish arriving at the spawning ground does not appear to influence survival, in contradiction to the results of other studies, which focused on earlier components of Pacific salmon spawning migrations. Fisheries adjacent to spawning sites represent the end of the continuum of salmon fisheries that begin with the high seas fishery and extend through the coastal and riverine environments. The mortality rates in this study should be interpreted cautiously by management until research efforts are broadened to provide a better understanding of how postrelease outcomes at different life stages compare in natural systems and under conditions more representative of real fisheries.

Population-Specific Consequences of Fisheries-Related Stressors on Adult Sockeye Salmon *

Article

Full-text available

Nov 2012
PHYSIOL BIOCHEM ZOOL

Abstract The objective of this study was to determine whether fisheries-related stressors differently influence two populations of adult sockeye salmon (Oncorhynchus nerka) with shared migration timing and location but where one population (i.e., Harrison) spawns 1 mo after the other (i.e., Weaver). Four stressor treatments were used following beach seine capture: (1) immediate release, (2) release after 10-15 min in the beach seine, (3) an additional 3-min gill net entanglement and 1-min air exposure, and (4) an additional 3-min tangle net simulation and 1-min air exposure. A comprehensive acoustic telemetry array and manual tracking revealed that survival was low overall, with more Weaver fish (34.2% of 38 tagged) reaching spawning areas compared to Harrison fish (17.8% of 78 tagged). For the Harrison population but not the Weaver, the gill net treatment influenced immediate (i.e., survived treatment) and short-term (i.e., 5-d postrelease) survival as well as survival to reach spawning areas. Harrison fish were more likely to be injured by the treatment, and reflex impairment predicted their short-term and long-term survival. Physiological condition did not differ between populations at the time of release, although both populations showed signs of severe physiological disturbances from the gill and tangle net simulations. These results suggest that even short durations of gill or tangle net entanglement can result in profound population-specific physiological disturbances and mortality. The notion that there can be population-specific variation in response to fisheries encounters adds complexity to management and provides further evidence for intraspecific differences in migration success.

From transcriptome to biological function: Environmental stress in an ectothermic vertebrate, the coral reef fish Pomacentrus moluccensis

Article

Full-text available

Feb 2007
BMC GENOMICS

Our understanding of the importance of transcriptional regulation for biological function is continuously improving. We still know, however, comparatively little about how environmentally induced stress affects gene expression in vertebrates, and the consistency of transcriptional stress responses to different types of environmental stress. In this study, we used a multi-stressor approach to identify components of a common stress response as well as components unique to different types of environmental stress. We exposed individuals of the coral reef fish Pomacentrus moluccensis to hypoxic, hyposmotic, cold and heat shock and measured the responses of approximately 16,000 genes in liver. We also compared winter and summer responses to heat shock to examine the capacity for such responses to vary with acclimation to different ambient temperatures. We identified a series of gene functions that were involved in all stress responses examined here, suggesting some common effects of stress on biological function. These common responses were achieved by the regulation of largely independent sets of genes; the responses of individual genes varied greatly across different stress types. In response to heat exposure over five days, a total of 324 gene loci were differentially expressed. Many heat-responsive genes had functions associated with protein turnover, metabolism, and the response to oxidative stress. We were also able to identify groups of co-regulated genes, the genes within which shared similar functions. This is the first environmental genomic study to measure gene regulation in response to different environmental stressors in a natural population of a warm-adapted ectothermic vertebrate. We have shown that different types of environmental stress induce expression changes in genes with similar gene functions, but that the responses of individual genes vary between stress types. The functions of heat-responsive genes suggest that prolonged heat exposure leads to oxidative stress and protein damage, a challenge of the immune system, and the re-allocation of energy sources. This study hence offers insight into the effects of environmental stress on biological function and sheds light on the expected sensitivity of coral reef fishes to elevated temperatures in the future.

Adaptive protocols identify sources of post-capture mortality in radio-marked wild turkeys

Article

Full-text available

Aug 2023

Context Stress or injury resulting from capture and marking of animals is a potential cause of mortality following release. Multiple methods have been developed to identify sources of post-capture mortality, but these are most often applied following completion of field work to identify an appropriate censor window for other analyses. Aims Following unacceptable levels of post-capture mortality (13 of 53) in radio-marked individuals in the first year of a larger wild turkey research project in Maine, USA, we assessed post-capture survival as data became available to inform proactive changes to capture protocols, with the goals of improving animal welfare and data quality. Methods We evaluated potential sources of post-capture mortality related to the capture and marking process, individual characteristics of the turkey, and local weather conditions. We then used results from the preliminary analysis to inform adaptive changes to capture protocols in subsequent years and confirmed the effectiveness of these changes through a final analysis. Key results We found that greater handling time was positively correlated with increased post-capture survival, possibly in response to releasing turkeys in larger groups to facilitate regrouping. We also found that transmitter style impacted post-capture survival, such that female turkeys fitted with backpack-style transmitters experienced a survival rate of 0.787 (0.677–0.861 95% CI), compared with 0.903 (0.538–0.976 95% CI) for those fitted with a necklace transmitter, although adjustments to the fit of backpack transmitters appeared to help mitigate such issues. Conclusions Following informed adjustments to our capture protocols, we observed a dramatic increase in post-capture survival such that no mortalities were experienced in the first 30 days post capture in the final year of our study (n = 65). Although our estimated censor window was similar to other studies (~10 days), differences in effects of external stressors further the need for adaptive capture protocols because local stressors and risks may vary according to climate and ecosystem characteristics such as predator communities and habitat type. Implications We recommend that when possible, investigators continuously assess their protocols throughout the capture process and adapt accordingly to limit negative repercussions of capture and handling to wildlife.

Stress history affects heat tolerance in an aquatic ectotherm (Chinook salmon, Oncorhynchus tshawytscha)

Article

May 2022
J THERM BIOL

The stress history of an ectotherm may be a pivotal predictor of how they cope with rapid spikes in environmental temperature. An understanding of how stressors in habitats and commercial operations affect ectotherm heat tolerance is urgently required so that management actions can be informed by thermal physiology. We hypothesised that brief exposure to mild stress would heighten tolerance to subsequent heat stress, indicative of a cross-tolerance interaction, whereas exposure to severe stress would reduce heat tolerance, reflecting a cross-susceptibility interaction. To test this hypothesis, we assessed how three acute stressors (salinity shock [10 or 33 ppt for 2 h]), air exposure (1 or 5 min) and crowding [95.6 kg m⁻³ for 2 h]), commonly experienced by fish, affected the heat tolerance (measured as critical thermal maximum, CTMAX) in juvenile Chinook salmon (Oncorhynchus tshawytscha). Fish were exposed to one of the three stressors and left for 24 h of recovery prior to measuring CTMAX. Heat tolerance was improved by ∼0.6 °C in fish exposed to salinity shock (10 ppt) and air exposure (5 min) compared to unstressed controls, demonstrating cross-tolerance. However, the development of cross-tolerance was non-linear with stressor severity, and crowding stress had no effect on CTMAX. Together these results show that some forms of stress can heighten acute heat tolerance in ectotherms, but the development of cross-tolerance is highly specific to both stressor type and stressor severity.

The Effects of Capture and Time Out of Water on Sablefish (Anoplopoma fimbria) Reflexes, Mortality, and Health

Article

Full-text available

Jun 2021

It is unknown if capture coupled with time out of water on-deck affect sablefish (Anoplopoma fimbria) health and reflexes, and whether it contributes to acute or delayed mortality. In this study, 35 sablefish were caught using hook-and-line gear and given six reflex tests after capture. Thirty-two were subsequently transported to the laboratory, held for 45–52 days, and then experimentally held out of the water for either 0, 3, 6, or 11 min. After 7–10 days of holding in the laboratory after the experiment, to monitor for mortalities, reflexes were tested for a second time and necropsies and histopathology were performed. There were no histological findings and no mortalities; however, parasites and minor inflammation were observed. All occurrences were not a result of capture or experiments. Some reflexes were absent after capture (77% could right themselves, 69% responded to a tail grab, and 57% responded to sound.) The only test where the reflex did not improve to 100% in the laboratory was the sound reflex. The sound reflex was highest for control fish (63%) and there were no positive sound reflexes for fish held out of water for 11 min. The absence of reflexes may result in predation after release and present issues with feeding or communication.

Gill‐Net Fishing Effort Predicts Physical Injuries on Sockeye Salmon Captured near Spawning Grounds

Article

Mar 2019

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.

Fisheries capture and infectious agents are associated with travel rate and survival of Chinook salmon during spawning migration

Article

Jan 2019
FISH RES

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.

Visible Gill-Net Injuries Predict Migration and Spawning Failure in Adult Sockeye Salmon

Article

Full-text available

Jul 2018

Fish that survive non‐take fisheries interactions may subsequently die; a phenomenon generically termed fisheries‐related incidental mortality (FRIM). Gillnets, which typically asphyxiate fish and visibly damage their integument, inflict higher rates of FRIM than other commonly used gears. To better define FRIM associated with gillnet encounters, an observational study coupled with biotelemetry measured migration survival and spawning success of a sockeye salmon population during the final 45 km of their freshwater spawning migration (in 2014, 2015, and 2016). The daily prevalence of gillnet injuries ranged from 0% to 80% of fish, resulting in annual prevalence of 21% to 29% for females and 13% to 22% for males (over three years). Fish with visible gillnet wounds had a 16% lower probability of completing their migration and female fish with gillnet wounds had an 18% lower probability of successfully spawning. As a result, the annual proportion of effective female spawners dying in the final 45 km of their migration due to gillnet injuries was estimated to range from 3.8% to 9.9% (500 to 1600 females). In addition, stray sockeye salmon from upriver populations commonly died at the tagging site, and visible gillnet injuries were observed in half of these fish in a year with high mortality. If wild salmon populations continue to decline as climate change progresses, fisheries managers will be under greater pressure to minimize FRIM. This article is protected by copyright. All rights reserved.

Location-specific consequences of beach seine and gillnet capture on upriver-migrating sockeye salmon migration behavior and fate

Article

Full-text available

Feb 2018

Fish released after capture, or fish interacting with gear but escaping, sometimes experience fishing-related incidental mortality (FRIM). For adult Pacific salmon migrations, knowing the magnitude of FRIM is important to estimate escapement accurately and to understand the total impact of a specific fishery. To determine how multiple gear types are associated with FRIM at different levels of maturity, we captured sockeye salmon (Oncorhynchus nerka) by both gill net and beach seine at three locations along their migration route (10%, 26%, and 72% of a 500 km freshwater migration) and determined their migratory success using biotelemetry. FRIM was higher for fish captured by gill net except at the location closest to spawning grounds. In addition, salmon captured by gill net at the lower river locations temporarily delayed migration, potentially indicating a requirement for lengthier recovery time compared with beach-seined fish. These results provide the first empirical and parallel comparison of these two common in-river fishing methods for salmon, revealing clear differences in FRIM between the two fishing methods in lower river fisheries and the importance of maturity.

The Impacts of Bycatch from the Atlantic Tropical Tuna Purse Seine Fishery on Ecosystem Structure and Function

Thesis

Full-text available

Jan 2016

Francesca C. Forrestal

Hematología de juveniles de pacu, Piaractus mesopotamicus (Holmberg, 1887) alimentado con raciones suplidas con manan oligosacáridos (MOS)

Article

Full-text available

Mar 2014

Characteristics and discard mortality of octopus bycatch in Alaska groundfish fisheries

Article

Full-text available

Sep 2016
FISH RES

Octopus are caught incidentally in several US federally-managed trawl, longline, and pot fisheries in Alaska. The majority caught are giant Pacific octopus Enteroctopus dofleini. Recent changes in fisheries management in Alaska have resulted in the creation of an octopus species complex with annual catch limits, leading to increased interest in management and catch accounting for this data-poor assemblage. This study characterized the incidental octopus catch in Alaska groundfish fisheries and the mortality rate of octopus caught and discarded at sea. Onboard fisheries observers collected data on octopus weight, sex, and condition at discard in a variety of Alaska groundfish fisheries from 2006 to 2011. A field study aboard a commercial pot-fishing vessel examined delayed mortality resulting from the capture process in giant Pacific octopus during routine pot fishing. Octopus incidental catch varied widely in size and condition at capture for various fishing gear types. Vessels fishing using pot gear captured larger octopus than vessels using longline or trawl gear. Initial condition at capture was best in pot gear, with over 90% of octopus discarded from pot vessels alive in excellent condition. Octopus taken in trawl gear had the highest immediate mortality rate, with 68–94% dead or injured at discard. Giant Pacific octopus held for 24–60 h following pot capture showed no signs of delayed mortality or decline in condition. These results suggest that assuming 100% mortality of discarded octopus may overestimate fishing impacts.

THE EPIDEMIOLOGICAL STATUS OF PAV1, AND THE EFFECTS OF INFECTION ON CARIBBEAN SPINY LOBSTER (PANULIRUS ARGUS) CONDITION, OLFACTION, AND PREDATION RISK

Article

Aug 2009

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. Exponer a los peces al aire tras ser capturados influencia su supervivencia y comportamiento a la hora de liberarlos. La exposición al aire causa hipoxia aguda y maltrata las lamelas de las branquias, lo que resulta en estrés fisiológico y daño físico, el cual se incrementa a medida que se expone el pez al aire por más tiempo. La duración de la exposición al aire es una medida relevante y fácil de cuantificar tanto para los pescadores como para los manejadores y, por lo tanto, brinda un punto de referencia para mejorar la supervivencia tras la liberación. Aun así, a los pescadores rara vez se les dan recomendaciones específicas que van más allá de “minimizar” la exposición de los peces. Esta es una recomendación subjetiva que potencialmente causa confusión y no se acata. Aquí se discute y resume la literatura referente a los límites de exposición al aire tanto en pesquerías comerciales como recreativas, los factores que afectan esos límites y se identifican huecos del conocimiento que limitan el entendimiento de la tolerancia de los peces capturados cuando se les expone al aire. Exposer les poissons à l'air après leur capture influe sur la survie et le comportement après remise à l'eau. L'exposition à l'air provoque une hypoxie aiguë et des dommages physiques aux lamelles des branchies, ce qui entraîne un stress physiologique et des dommages physiques qui augmentent avec la durée d'exposition à l'air. La durée d'exposition à l'air est une mesure pertinente et facilement quantifiée pour les pêcheurs et les gestionnaires et peut donc constituer une référence définitive pour l'amélioration de la survie après remise à l'eau. Pourtant, les pêcheurs reçoivent rarement des recommandations spécifiques autres que de simplement « minimiser » l'exposition à l'air. Cette recommandation est subjective, et peut semer la confusion et conduire à la non-conformité. Ici, nous discutons et faisons le point sur la documentation concernant les seuils d'exposition à l'air à la fois pour la pêche commerciale et la pêche récréative, les facteurs influençant ces seuils, et identifions les lacunes dans les connaissances qui limitent notre compréhension de la tolérance à l'exposition de l'air chez les poissons capturés.

Understanding the consequences of fisheries-related stressors on adult migrating Pacific salmon

Article

Full-text available

Jan 2012

Michael Donaldson

At-vessel mortality and blood biochemical status of elasmobranchs caught in an Australian commercial longline fishery

Article

Full-text available

May 2015

This study investigates mortality of sharks in a commercial longline fishery in Australia. To examine the rate and biological, environmental and technological factors contributing to at-vessel mortality, four setlines with 120 gangions possessing ‘hook timers’ were deployed daily (for 7h and 14h) using conventional gears from two commercial fishing vessels during 2013. A total of 689 animals across 22 species and including 18 elasmobranchs were landed. For the five species (Carcharhinus spp.), and one genus (Sphyrna spp) where there were sufficient numbers for analysis, generalised linear mixed models showed that species and the elapsed time spent on the line after hooking were the strongest predictors of at-vessel mortality, with spinner (Carcharhinus brevipinna), blacktip (C. limbatus) and hammerhead (Sphyrna spp) sharks exhibiting the highest death rates. The variables which best explained mortality, included: (i) sex of the caught sharks, and the interaction between species with (ii) capture depth, and (iii) the elapsed time spent on the line after hooking. For the subset of dusky (C. obscurus) and sandbar (C. plumbeus) sharks examined for physiological status at the point of capture, very few of the 13 chosen blood analytes varied significantly. Given the observed high mortality rates and stress associated with the time spent on the line after capture, operational changes to reduce these adverse impacts should be considered. Even simple changes such as shorter soak times could considerably mitigate these impacts.

Bycatch mortality of endangered coho salmon: Impacts, solutions, and aboriginal perspectives

Article

Oct 2014

We used biotelemetry and human dimensions surveys to explore potential solutions to migration mortality of an endangered population of coho salmon caught as bycatch in an aboriginal beach seine fishery. From 2009 to 2011, 182 wild coho salmon caught as bycatch in the lower Fraser River (Canada) were radio-tagged and tracked as they attempted to complete their migrations to natal spawning areas over 300 km upstream. Failure to survive to reach terminal radio receiving stations averaged 39% over three years. This mortality estimate is low compared to those obtained from telemetry studies on other salmon fisheries in the Fraser River. However, this value is markedly higher than the mortality estimate currently used to manage the fishery's impact. It is also in contrast to the perceptions of the majority of aboriginal fishers, who did not think survival of coho salmon is affected by capture and release from their fishery. Increased probability of survival was associated with lower reflex impairment, which is consistent with previous findings. Reflex impairment was positively correlated with entanglement time, suggesting that greater efforts by the fishers to release bycatch from their nets quickly would minimize post-release mortality. Survey responses by aboriginal fishers also suggested that they are receptive to employing new bycatch handling methods if they are shown to increase post-release survival. However, attempts to facilitate revival of a subset of captured fish using cylindrical in-river recovery bags did not improve migration success. Fisheries managers could use the new information from this study to better quantify impacts and evaluate different harvest options. Since aboriginal fishers were receptive to using alternate handling methods, efforts to improve knowledge on minimizing reflex impairment through reductions in handling time could help increase bycatch survival. Such a direct integration of social science and applied ecology is a novel approach to understanding conservation issues that can better inform meaningful actions to promote species recovery.

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

Technical Report

Full-text available

Apr 2014

Hematology of juvenile pacu, Piaractus mesopotamicus (Holmberg, 1887) fed graded levels of mannan oligosaccharides (MOS)

Article

Full-text available

Feb 2014

Intensification of aquaculture production systems exposes fish to numerous stressors, which may negatively affect their health. This study determined the effects of increasing levels of dietary mannan oligosaccharides (ActiveMOS (R)-Biorigin) on biochemical and hematological parameters of juvenile pacu, Piaractus mesopotamicus. Fish (44.04 +/- 5.27 g) were randomly distributed into 24 tanks (500 L; 10 fishes per tank) and fed during 63 days with a commercial diet supplemented with 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5 and 2.0% MOS. Blood samples were collected at 42 and 63 trial. Red blood cell count (RBC) and total plasmatic protein were affected by dietary MOS levels (P < 0.05). Fish fed 1.0% dietary MOS presented higher neutrophils numbers when compared to fish fed control diet and fish fed 1.5% MOS for 42 days presented significant higher granulocytic cell numbers. During trial fish presented increased (P < 0.05) hematocrit, mean corpuscular volume, mean corpuscular hemoglobin and plasmatic glucose concentrations and decreased (P < 0.05) RBC, hemoglobin concentration, mean corpuscular hemoglobin concentration, white blood cell and differential leukocyte count. Dietary MOS levels did not present prebiotic effects for pacu and did not minimize stress effects on hematological and biochemical parameters for the species.

Assessing the impacts of gillnetting in Tasmania: Implications for by-catch and biodiversity

Technical Report

Full-text available

Aug 2014

In Tasmania, both recreational and commercial gillnetting is permitted. This study, conducted by the Institute for Marine and Antarctic Studies between 2010 and 2013, represents the most comprehensive investigation into the Tasmanian gillnet fishery and its implications for by-catch and biodiversity. Gillnet catch composition (target, by-product, by-catch), post release survival, interactions with threatened, endangered and protected species, and implications of management changes on gillnetting practices were investigated. In addition, catch composition and abundances of key gillnet species over the past 20 years were examined using a range of historical data. This information was then used to inform an ecological risk assessment to identify the vulnerabilities of the species impacted by gillnetting. Background Recreational gillnet fishers target a wide variety of species with the main target species being Blue Warehou, Bastard Trumpeter, Atlantic Salmon (escapees from marine farms), Australian Salmon and Yelloweye Mullet. The commercial fishery is a dynamic multi-species fishery with fishers adapting to species availability, market preferences and opportunities. Commercial fishers target similar species to recreational fishers although in the early 1990s a fishery targeting Banded Morwong for the domestic live fish trade developed rapidly and the majority of the commercial effort is now directed at this species. Over the past decade there have been a number of management initiatives, including a prohibition on overnight recreational netting (with the exception of Macquarie Harbour), introduction of attendance requirements for commercial night gillnetting, and more recently the introduction of maximum soak times for both the recreational and commercial fishery, which have been designed to improve fishing practices and reduce wastage and impacts on non-target species. Despite this, there have been conspicuous declines in the abundance of several key gillnet species along with increasing community concern about the ecological impacts of gillnetting. There is a need, therefore, to better understand how recent management initiatives have influenced netting practices and to objectively assess the risks and impacts on target and non-target species. Ultimately such an understanding will be pivotal in informing the on-going debate over the future management of gillnetting in Tasmania. Aims/objectives 1 Synthesise available gillnetting information, with particular reference to links between operational parameters and catch composition 2 Determine catch composition and levels of by-catch associated with the main commercial gillnet fisheries 3 Assess implications of recent management changes on recreational netting practices 4 Assess the relationships between gillnet soak times, capture condition and by-catch survival 5 Evaluate the impacts of gillnetting on the biodiversity of key inshore ecosystems and potential strategies to mitigate these impacts Methodology In relation to Objective 1 available information based on previous research and commercial gillnet catch sampling studies were collated and assessed to examine for regional and temporal changes in target and non-target species abundance. For Objective 2 a variety of data sources were investigated, including commercial logbook data, previous recreational fishing survey data, on-board commercial catch sampling and results from research netting. Objective 3 was primarily addressed through a survey of recreational gillnet fishers and the synthesis of trends based on previous recreational fishing surveys. For Objective 4 research gillnetting trials involving post release survival experiments, along with on-board commercial catch sampling, provided information about operational relationships between soak times, catch condition and by-catch survival. Finally, Objective 5 involved the synthesis of information reported for the present study integrated with long-term biodiversity monitoring data based on underwater visual census surveys and a formal ecological risk assessment of the major Tasmanian gillnet fisheries. Results/key findings Gillnet fisheries target a range of habitats, including reef and non-reef areas, and land a wide diversity of fish species, with over 90 taxa reported in commercial catch returns. The recreational gillnet fishery targets much the same species as the commercial sector and there is considerable overlap between sectors in the areas fished. For both sectors comparatively few species account for the majority of the landings. Catches in the Banded Morwong fishery are dominated by the target species (>85%), only Bastard Trumpeter and Longsnout Boarfish are of any significance amongst the other species harvested. The general graball net fisheries target a range of species with Bastard Trumpeter, Blue Warehou and Australian Salmon key components of the catch. Bastard Trumpeter, Blue Warehou and Atlantic Salmon (escapees from fish farms) comprise the main species retained by the recreational gillnet sectors. Catches in the commercial small mesh and recreational mullet net fisheries although low, are dominated by Australian Salmon, ‘Pike’ (Snook and Longfin Pike) and Yelloweye Mullet. The difference in catch composition between graball and small mesh nets is due to mesh selectivity, along with the prohibition of setting recreational mullet nets over reef. In each of the gillnet fisheries a component of the catch is not retained (by-catch), either because of regulation (size or catch limits, closed seasons for selected species, prohibited or protected species) or because of market and/or fisher preferences. The by-catch component, as a proportion of total catch numbers was found to be relatively high; 52% for Banded Morwong fishers, 49% for the general graball fishery, 66% for the small mesh fishery and 35% for the recreational gillnet fishery, although the latter may be an underestimate as it is based on self-reported information. A wide diversity of species that included target species comprised the by-catch component, but in terms of overall contribution to by-catch numbers relatively few species accounted for the bulk of the discards. The main non-target by-catch species included Draughtboard Shark, Marblefish, Bluethroat Wrasse, Leatherjackets and Skates/Rays. Discard rates for by-catch species tended to exceed 80%, whereas discard rates for species typically targeted or retained as by-product typically ranged between 10 – 20%. Capture condition (based on an assessment of physical damage and responsiveness) and delayed mortality rates (based on tank survival trials) of gillnet caught fish varied between species and were influenced by operational factors including soak time and in some instances season. Several species were particularly resilient, suffering minimal physical damage and low rates of initial and delayed mortality, and experienced high overall post release survival (PRS) rates (>85%) irrespective of soak duration. Species in this category included Banded Morwong, Bastard Trumpeter, Marblefish, Draughtboard Shark, Purple Wrasse, Leatherjackets, Longsnout Boarfish and Skates/Rays. Species with moderately high PRS rates (70 – 85%) included Bluethroat Wrasse, Elephantfish, Whitespotted Dogfish and Bluestriped Goatfish. Southern Sand Flathead, Gummy Shark and Jackass Morwong had lower PRS rates (50 – 70%), while survival rates for a suite of other species including Blue Warehou, Australian Salmon and Atlantic Salmon were quite poor (< 50%). A number of interactions with threatened, endangered and protected species (TEPS) were observed in this study. Fur Seals were commonly observed in the vicinity of gillnets and the majority of direct interactions with the nets involved provisioning (removal and consumption of entangled fish); there were no instances involving entanglement of seals. Entanglement and drowning of seabirds (Cormorants and Penguins) in gillnets was observed, though such incidences were rare making it difficult to identify contributing factors. In Macquarie Harbour, the endangered Maugean Skate was regularly caught in gillnets set in depths of between about 5-15 m. Although the majority of individuals captured were in excellent condition and lively when released, a small proportion of those captured in overnight deployments were either in poor condition or had died, confirming some by-catch mortality in these longer soak times. Analyses of historic gillnetting data and underwater visual census data revealed that there have been some changes to species abundance and species composition over the past 20 years but, on the whole, this has been dominated by the decline in Banded Morwong abundance and inter-annual variability in the abundance of Bastard Trumpeter and Blue Warehou. Marblefish abundances have declined in most regions since the mid-1990s despite being rarely retained and having high post release survival. Previous fishing and poor handling practices may have resulted in higher than expected by-catch mortality. Overnight netting was a common practice for recreational fishers prior to its prohibition in all areas apart from Macquarie Harbour. This ban appears to have had a significant impact on netting effort, not only has it achieved a marked reduction in the proportion of overnight sets but there has been a substantial reduction in overall recreational netting effort. Virtually all recreational gillnet fishers engage in other types of recreational fishing, only a small proportion identified gillnetting as their main recreational fishing activity or that they would consider giving up fishing altogether if they could not gillnet. There was general agreement amongst recreational fishers that recent management changes had been effective in improving fishing practices and in reducing wastage and by-catch. A formal ecological risk assessment was conducted based on four sub-fisheries that make up the Tasmanian gillnet fishery. These are the large mesh graball (Banded Morwong) sub-fishery, the general graball net fishery, comprised of reef and non-reef sub-fishery components, the latter occurs predominately within shark refuge areas, and the small mesh fishery, which includes commercial small mesh and recreational mullet net components. Level 1, Scale, Intensity and Consequence Analysis identified that target, by-catch/by-product and TEPS components had consequence scores above moderate for several hazards (principally ‘capture by fishing’, ‘fishing without capture’ and ‘external hazards’). By contrast habitats and communities were judged to be impacted with low consequence by each of the gillnet fisheries and thus were not considered in the Level 2 Productivity Susceptibility Analysis (PSA) assessment. The PSA identified a number of species at high risk, each specific to a sub-fishery and a result that reflects differences in mesh selectivity as well as differences in the spatial coverage of the fisheries. Bastard Trumpeter was the only species ranked as high risk in the graball (reef) sub-fishery, largely because inshore reefs represent the core habitat for juveniles and sub-adults and the species is particularly susceptible to gillnet capture. None of the species that interacted with the graball (Banded Morwong) sub-fishery were ranked as high risk, predominantly due to the high level of selectivity achieved for the target species by the large mesh size. Atlantic Salmon and Rainbow Trout were ranked as having high vulnerability in the non-reef sub-fishery but, being introduced exotics, this represents a positive ranking, with fishing pressure contributing to their removal from the environment. Maugean Skate and Whitespotted Dogfish were also identified as high vulnerability species; the former has a highly restricted distributional range, presumed low population size and key biological attributes are unknown, and the latter on the other hand is amongst the least productive chondrichthyan species known. Within the small mesh fishery, the Great Cormorant, Rock Flathead and Snook were ranked as having high vulnerability, although low catches and wide distribution outside of Tasmania waters suggest the actual vulnerabilities for the fish at least may not be as high as implied by this analysis. Of the marine mammals, other seabirds and other chondrichthyans considered in the PSA most were ranked as medium vulnerability, mainly due to low productivity levels. Implications for relevant stakeholders This study has identified a number of issues that have particular relevance to the future management of gillnetting in Tasmania, noting that gillnet usage has emerged as an area of particular focus in the 2014 review of the Scalefish Management Plan and while it is beyond the scope of the present study to make recommendations on whether or not recreational gillnetting should be banned, this study does provide information that will assist in informing this debate. There is little doubt that gillnetting has had demonstrable impacts on populations of the key target species, in particular Banded Morwong, Blue Warehou and Bastard Trumpeter. There are specific management measures now in place for Banded Morwong (quota management) and Blue Warehou (Commonwealth stock rebuilding strategy) to help sustain and rebuild populations. There is also a case for management intervention to reduce fishing pressure on Bastard Trumpeter, especially given its high vulnerability ranking; such measures could include expansion of no-netting areas, increase in legal minimum size and/or reduction of bag or trip limits. This study has established that post release survival of many of the key by-catch species is likely to be high, a situation enhanced by improvements in fishing practices over the past few years. While there would be some benefit, albeit minor, for by-catch survival in reducing the maximum soak time to less than six hours, the prohibition on night netting and introduction of the soak time regulations appear to have been quite successful in reducing wastage and impacts on non-target species. Interactions with seabirds appear to be an inevitable consequence of gillnetting in shallow coastal waters, though in the main they do tend to occur with low frequency. However, if gillnets are deployed near rookeries, or in corridors that seabirds use to access rookeries, there is potential for interactions involving greater numbers than occurred in the present study. In order to minimise this risk, consideration should be given to establishing no-netting areas around key rookeries. The development of a code of practice for gillnet usage that includes voluntary cessation of gillnet activities while flocks of seabirds (especially Short-tailed Shearwaters) are present in high net use areas would also help reduce the risk of interactions. This study has established that the endangered Maugean Skate is particularly susceptible to capture in gillnets and although the vast majority are expected to survive, some mortalities, especially in overnight sets, are expected. As a listed species, options to reduce such interactions need to be considered. There are a number of strategies that would help miminise Maugean Skate by-catch and mortality, these include a ban on overnight netting (bringing Macquarie Harbour into line with the remainder of the state), an expansion of the areas closed to netting and/or restricting gillnet usage within Macquarie Harbour to shallow waters (< ~5 m). Implemention of a strategy based on fishing depth may be best achieved through a code of practice and education, noting that the main target species – Atlantic Salmon and Flounder – are commonly caught in the shallows. Deployment of gillnets in shallow waters would also have the benefit of reducing the by-catch of Whitespotted Dogfish, assessed along with the Maugean Skate as having high vulnerability.

Hematology of juvenile pacu, Piaractus mesopotamicus (Holmberg, 1887) fed graded levels of mannan oligosaccharides (MOS)

Article

Full-text available

Jun 2014

Ricardo Sado

Intensification of aquaculture production systems exposes fish to numerous stressors, which may negatively affect their health. This study determined effects of increasing levels of dietary mannan oligosaccharides (ActiveMOS® - Biorigin) on biochemical and hematological parameters of juvenile pacu, Piaractus mesopotamicus. Fish (44.04 ± 5.27 g) were randomly distributed into 24 tanks (500L; 10 fishes per tank) and fed during 63 days with a commercial diet supplemented with 0.0; 0.2; 0.4; 0.6; 0.8; 1.0; 1.5 and 2.0% MOS. Blood samples were collected at 42 and 63 trial. Red blood cell count (RBC) and total plasmatic protein were affected by dietary MOS levels (P < 0.05). Fish fed 1.0% dietary MOS presented higher neutrophils numbers when compared to fish fed control diet and fish fed 1.5% MOS for 42 days presented significant higher granulocytic cell numbers. During trial fish presented increased (P < 0.05) hematocrit, mean corpuscular volume, mean corpuscular hemoglobin and plasmatic glucose concentrations and decreased (P < 0.05) RBC, hemoglobin concentration, mean corpuscular hemoglobin concentration, white blood cell and differential leukocyte count. Dietary MOS levels did not present prebiotic effects for pacu and did not minimize stress effects on hematological and biochemical parameters for the species.

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.

Disentangling the Roles of Air Exposure, Gill Net Injury, and Facilitated Recovery on the Postcapture and Release Mortality and Behavior of Adult Migratory Sockeye Salmon ( Oncorhynchus nerka ) in Freshwater

Article

Full-text available

Jan 2014

We sought to improve the understanding of delayed mortality in migrating sockeye salmon (Oncorhynchus nerka) captured and released in freshwater fisheries. Using biotelemetry, blood physiology, and reflex assessments, we evaluated the relative roles of gill net injury and air exposure and investigated whether using a recovery box improved survival. Fish ( ), captured by beach seine, were allocated to four treatment groups: captured only, air exposed, injured, and injured and air exposed. Only half of the fish in each group were provided with a 15-min facilitated recovery. After treatment, fish were radio-tagged and released to resume their migration. Blood status was assessed in 36 additional untagged fish sampled after the four treatments. Compared with fish sampled immediately on capture, all treatments resulted in elevated plasma lactate and cortisol concentrations. After air exposure, plasma osmolality was elevated and reflexes were significantly impaired relative to the control and injured treatments. Injured fish exhibited reduced short-term migration speed by 3.2 km/d and had a 14.5% reduced survival to subnatal watersheds compared to controls. The 15-min facilitated recovery improved reflex assessment relative to fish released immediately but did not affect survival. We suggest that in sockeye salmon migrating in cool water temperatures (∼13°–16°C), delayed mortality can result from injury and air exposure, perhaps through sublethal stress, and that injury created additive delayed mortality likely via secondary infections.

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.

Factors Affecting Catch-and-Release Mortality of Bluefish

Article

Full-text available

Feb 2008

Recreational harvests of bluefish Pomatomus saltatrix along the U.S. coast from Maine to Florida exceed commercial harvests, and in recent years about 60–70% of angler-captured fish are released alive. The proportion of fish that survive hooking, handling, and release back to the ocean is unknown; however, if catch-and-release mortality is high, it may represent a significant component of the overall bluefish mortality rate. We estimated long-term (21-d) hooking mortality rates of field-captured bluefish and investigated the effects of various factors on postrelease mortality. Age, length, and the occurrence of bleeding were significant factors associated with catch-and-release mortality, which we estimated to be 38.8%. About 65% of the mortality was initial mortality, and the remainder was delayed mortality. We also performed a laboratory study to examine the physiological response of bluefish to two independent processes (hooking and release versus transfer in coolers to the laboratory) relevant to the field study. Laboratory-held fish that were hooked and released exhibited elevated concentrations of potassium in their blood, suggesting that they experienced either an osmotic imbalance or cellular damage. Laboratory-held fish exposed to the transfer treatment only exhibited osmotic imbalance (elevated plasma sodium concentration) and evidence of anaerobic metabolism (elevated plasma lactate concentration). Our findings indicate that bluefish age and size contribute to variable levels of metabolic stress and that delayed postrelease mortality is considerable.

PaV1 infection in the Florida spiny lobster (Panulirus argus) fishery and its effects on trap function and disease transmission

Article

Full-text available

Jan 2012

The Caribbean spiny lobster (Panulirus argus) supports the most economically valuable fishery in the Caribbean. In Florida, USA, the majority of the catch is landed in traps “baited” with live, sublegal-sized lobsters that attract other lobsters due to their social nature. This species is also commonly infected by the pathogenic virus Panulirus argus Virus 1 (PaV1). Here we describe a polymerase chain reaction (PCR) based assessment of the prevalence of PaV1 in the lobster fishery from the Florida Keys. We tested the effect of PaV1-infected lobsters in traps on catch and on transmission to other trapped, uninfected lobsters. We found that 11% of the lobsters caught in commercial traps were positive for the virus by PCR, but none of these animals showed visible signs of disease. We also tested whether healthy lobsters avoid diseased lobsters in traps. Traps into which we introduced an infected lobster caught significantly fewer lobsters than traps containing an uninfected lobster. Moreover, uninfected lobsters confined in traps with infected lobsters acquired significantly more PaV1 infections than those confined with uninfected lobsters. This study demonstrates the indirect effects that pathogens can have on fisheries and the unintended consequences of certain fishery practices on the epidemiology of a marine pathogen.

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.

The physiological response to anthropogenic stressors in marine elasmobranch fishes: A review with a focus on the secondary response

Article

Oct 2011

Elasmobranchs (sharks, rays, and skates) are currently facing substantial anthropogenic threats, which expose them to acute and chronic stressors that may exceed in severity and/or duration those typically imposed by natural events. To date, the number of directed studies on the response of elasmobranch fishes to acute and chronic stress are greatly exceeded by those related to teleosts. Of the limited number of studies conducted to date, most have centered on sharks; batoids are poorly represented. Like teleosts, sharks exhibit primary and secondary responses to stress that are manifested in their blood biochemistry. The former is characterized by immediate and profound increases in circulating catecholamines and corticosteroids, which are thought to mobilize energy reserves and maintain oxygen supply and osmotic balance. Mediated by these primary responses, the secondary effects of stress in elasmobranchs include hyperglycemia, acidemia resulting from metabolic and respiratory acidoses, and profound disturbances to ionic, osmotic, and fluid volume homeostasis. The nature and magnitude of these secondary effects are species-specific and may be tightly linked to metabolic scope and thermal physiology as well as the type and duration of the stressor. In fishes, acute and chronic stressors can incite a tertiary response, which involves physiological changes at the organismal level, thereby impacting growth rates, reproductive outputs or investments, and disease resistance. Virtually no studies to date have been conducted on the tertiary stress response in elasmobranchs. Given the diversity of elasmobranchs, additional studies that characterize the nature, magnitude, and consequences of physiological stress over a broad spectrum of stressors are essential for the development of conservation measures. Additional studies on the primary, secondary, and tertiary stress response in elasmobranchs are warranted, with particular emphasis on expanding the range of species and stressors examined. Future studies should move beyond simply studying the effects of known stressors and focus on the underlying physiological mechanisms. Such studies should include the coupling of stress indicators with quantifiable aspects of the stressor, which will allow researchers to test hypotheses on survivorship and, ultimately, derive models that effectively link physiology to mortality. Studies of this nature are essential for decision-making that will result in the effective management and conservation of these species.

Simulated fishing experiments for predicting delayed mortality rates using reflex impairment in restrained fish

Article

Jun 2007

Michael W. Davis

Davis, M. W. 2007. Simulated fishing experiments for predicting delayed mortality rates using reflex impairment in restrained fish. – ICES Journal of Marine Science, 64: 1535–1542. Development of efficient methods to predict discard and escapee mortality in fishing operations is essential to the conservation of sensitive fish stocks. For a few fisheries, mortality data are available from fishing experiments in the field; these require long-term holding or monitoring of fish in tanks, cages, or tag and recapture experiments to detect delayed mortality. A different approach to predicting discard and escapee mortality is to use reflex action mortality predictors (RAMP) consisting of relationships between mortality and reflex impairment for species of interest. Fish were towed in a net in the laboratory and then either restrained in foam-lined holders and rapidly tested for reflex impairment five minutes after towing, or held for up to 60 days to determine delayed mortality. Delayed mortality occurred up to 20 days after towing. RAMP was related to mortality with biphasic sigmoid functions. As fishing stressors increased in intensity, the first phase showed an increase in RAMP with no concomitant mortality. In the second phase, RAMP continued to increase, while mortality became apparent and increased. The measurement of RAMP in restrained fish on board fishing vessels during experiments to predict discard mortality and in caged free swimming fish to predict escapee mortality is feasible and advisable.

Mitigating discard mortality from dusky flathead Platycephalus fuscus gillnets

Article

Jun 2009

The mortalities and contributing parameters were estimated for key species discarded during commercial gillnetting (80 mm mesh) targeting dusky flathead Platycephalus fuscus in a southeastern Australian estuary. Bycatches (1470 individuals from 16 species over 11 deployments) were assessed for their immediate mortalities onboard the gillnetter, before subsamples (570 individuals from 11 species) were discarded into cages and monitored for their short-term fate over 4 d. Appropriate controls were concurrently caged and monitored. Blood samples were taken from some live meshed-and-discarded yellowfin bream Acanthopagrus australis and luderick Girella tricuspidata and analysed for plasma cortisol and glucose. Concomitantly angled fish were similarly sampled (to provide baseline estimates of blood physiology). The immediate mortalities of the abundant species ranged between 0 (undersize blue swimmer crab Portunus pelagicus <6 cm carapace length) and 70% (undersize P. fuscus <36 cm total length [TL]). Water temperature had a statistically significant positive relationship with the immediate mortality of G. tricuspidata and large-tooth flounder Pseudorhombus arsius, and TL had a significant negative relationship with the immediate mortality of black sole Synaptura nigra. Compared to baseline estimates, mean plasma cortsiol concentrations in meshed-and-discarded G. tricuspidata and A. australis were significantly greater, and approached levels comparable to most teleosts after peak stress. Mean glucose concentrations were not concomitantly elevated, possibly reflecting limited time between stress and sampling for some individuals. Short-term mortalities occurred throughout the entire 4 d monitoring period for most species and ranged from 0 (yellowfin leatherjacket Meuschenia trachylepis) to 29% (A. australis). Water temperature and TL were identified as having significant impacts similar to those described above on the delayed fate of A. australis and G. tricuspidata. The partitioned mortalities were combined to provide estimates of overall mortality (+/- SE) for the main species that ranged between 5.9 +/- 3.3% (P. pelagicus) and 76.9 +/- 7.8% (undersize P. fuscus). Discard mortality in this fishery could be mitigated by allowing fishers to retain a small percentage of undersize P. fuscus, restricting the deployment of nets in water temperatures >16 to 17 degrees C, and encouraging the careful removal of catches from meshes.

Dose-dependent effects of chemical immobilization on the heart rate of embryonic zebrafish

Article

Full-text available

Nov 2006

The small size and optical transparency of zebrafish embryos and larvae greatly facilitate modern intravital microscopic phenotyping of these experimentally tractable laboratory animals. Neither the experimentally derived dose-response relationships for chemicals commonly used in the mounting of live fish larvae, nor their effect on the stress of the animal, are currently available in the research literature. This is particularly problematic for IACUCs attempting to maintain the highest ethical standards of animal care in the face of a recent spate in investigator-initiated requests to use embryonic zebrafish as experimental models. The authors address this issue by describing the dose-dependent efficacy of several commonly used chemical mounting treatments and their effect on one stress parameter, embryo heart rate. The results of this study empirically define, for the first time, effective, minimally stressful treatments for immobilization and in vivo visualization during early zebrafish development.

Disease ecology of wild fish: opportunities and challenges for linking infection metrics with behaviour, condition, and survival

Article

Full-text available

Mar 2021

Surmounting evidence supports that infectious agents play a critical role in shaping fish physiology, behaviour, and survival. The exclusion of disease-causing agents from fisheries research has resulted in major knowledge gaps that may limit the predictive capacity of ecological models. A major barrier in wild fisheries epidemiology is the logistical constraints associated with observing disease and obtaining samples from free-ranging fish, restricting the vast majority of research to laboratory studies or aquaculture facilities. For fisheries ecologists, including infectious agents can provide greater insight into observed phenomena, particularly with respect to fish physiology (e.g., metabolism), movement (e.g., migration rates), behaviour (e.g., habitat selection), personality (e.g., bold versus shy), and survival. Here we provide a brief introduction to the current understanding of disease ecology in wild fish and describe technological advances in both epidemiology and fisheries and aquatic sciences that can be used in tandem to create comprehensive studies of disease ecology in wild fishes. Combining nonlethal sampling and molecular genetic-based identification methods with field studies creates vast opportunities for innovative study designs that have the potential to address the true complexity of aquatic ecosystems.

Stress Management and Welfare

Chapter

Dec 2016

1. Introduction 1.1. Defining Welfare2. Managing Stress in Fish 2.1. Considerations for Care of Wild Fish in Captivity2.2. The Impact of Psychological Stress2.3. Controlling and Preparing for Stress3. The Impact of Stress on Fish Welfare 3.1. Stress in Fisheries3.2. Stress in Aquaculture3.3. Stress in Recreational Fishing3.4. Stress in Ornamental Fish3.5. Stress in Research Within a Laboratory Context3.6. Stress and Welfare in Wild Fish3.7. Surgery and Anesthesia4. Conclusions and Future DirectionsStress poses a significant challenge to the health and welfare of fish in a variety of contexts. Preserving fish well-being has obvious benefits for aquaculture, fisheries management practices, large-scale fisheries, recreational fishing, research, and the ornamental fish industry. Healthy fish provide better economic return, contribute to population size, provide experimentally sound data, are attractive and pleasing to watch, and pose no risk to public health. However, many practices in each of these areas where fish are used cause stress and as such may impair fish welfare. The impact of routine procedures that fish are subject to is discussed to better understand how stress can be managed in captivity. The means of reducing stress and its deleterious effects on fish behavior, development, growth, reproduction, and immune function are considered as practical management tools that could be employed by those using fish if they wish to minimize stress and improve health. The opportunity to have a sense of control over stress or being able to anticipate and prepare for stress improves the ability of fish to cope with any stressors in their environment. Inescapable, unpredictable, or chronic stress leads to loss of control and allostatic overload. This can result in behavioral abnormalities leading to displaced aggression and stereotypical behavior. Thus, allowing fish to have other behavior options such as hiding or redirecting behavior can be provided by environmental enrichment. Conditioning fish to associate cues with the onset of a stress allows them to anticipate and prepare for stress, which can be beneficial. Operant conditioning, where fish can operate self-feeders, allows fish to control their own foraging behavior and also has positive effects on fish welfare. Providing the right kind of environmental and cognitive stimulation along with optimal environmental conditions, appropriate feeding regimes and social contact appear to be key to reducing stress in captive contexts if this is logistically possible. Practices in a variety of fish industries are considered where stress may be elevated with countermeasures suggested. Future studies should investigate implementing these factors to understand their impact in different circumstances and in different species if reducing stress is important. The development of robust stress indicators and automated alert systems based on behavior or environmental parameters to detect fish health will be vital for the assessment and alleviation of stress.

Valdimar Ingi Gunnarsson, Björn Björnsson og Einar Hreinsson 2009. Föngun á þorski. Hafrannsóknastofnunin. Hafrannsóknir nr. 148. 122 p.

Technical Report

Full-text available

Dec 2009

Valdimar Gunnarsson

ABSTRACT In an amendment of the law 38/1990 about fisheries management, approved 15 th May 2002, is stated that the Minister of Fisheries can annually allocate 500 ton cod quota for the fishing years 2001/2002 to 2005/2006. The amendment has been extended two times and recently until the fishing year 2014/2015. This quota is allo- cated to experimental on-growing of cod in cooperation with the Marine Research Institute. This report sum- marizes the results of the capture, transportion and adaptation of cod in recovery cages in Iceland in 2002-2008 and compares the outcome with the results from other countries. In the appendices there is advice about fish capture for ongrowing. In the years 2002-2008; 1,400 tons were captured in Danish seine, 600 tons in trawl, 500 tons in traps, mainly Newfoundland trap, and 500 tons in long line an d hand line. Danish seine and trawl are by far most important gear to capture cod for on-growing, but no major improvements have been made concerning gear construction. In some cases modification has been made to the cod-end with canvas-lining to reduces pressure on the fish when hauling on board and usually the trawlin g speed is only half that used in traditional fishery and the volume of the catch is limited to one lifting bag. To reduce mortality the cod-end is sometimes emptied directly into the recovery cage. Many types of pots and trap s have been tried with best success of the Newfoundland trap. Modification has been made of Newfoundland trap to allow the fish to swim through a tunnel located a few meters under sea level into the recovery cage. Many boats have used hooks to capture cod for on-growing but few with success. Best results have been achieved with long line when the line is kept for a short time in sea and fish removed manually from the hooks. Limited success has been obtained with capturing cod with gill nets. Experiments have been done to establish herds of cod around feeding stations and to capture the fish with lift net, hand line and one unsuccessful effort with pure seining. When capturing cod for on-growing the fish with limed vitality are remove d from the catch and bled. Only healthy and vigorous fish are used for on-growing. In some instance a syringe is used to release air from the gas bladder. Mortality is very different between gear s and has been very low in traps and pots. In shallow water (<15-20 m) mortality has maximally been a few percent in Danish seine but higher in deeper water especially during the summer months. Improved methodology during the last few years has resulted in low mortality of cod captured with trawl. The highest mort ality is when the fish is captured with long line and hand line. Fish tubs are used to transport of live cod in the smallest boats but special tanks located in the hold in large boats. These tanks are equipped with a false movable bottom to facilitate the emptying of the tank. The transport unit for live cod has a diffuser to increase the solubility of oxygen in sea water. Oxygen injection in transport unit has decreased mortality of cod during the summer time. In general the transportation mortality of cod has been low particularly when the fish have remained in the recovery cage for some time before being transported to the on-growing area. Upon delivery from the fishing boats, the cod is lethargic and needs to restore itself physiologically as well as to refill the gas bladder. Traditional cages have been used with success for recovery of small volumes of fish. In some instance a float attached at the center of the bottom is used to increase the flat bottom area and the capacity of the recovery cage. Recently the bigger boats have been us ing recovery cages with a flat and stiff bottom.

Seabird bycatch in the pelagic longline fishery off southern Africa

Article

Full-text available

Aug 2009

The waters around South Africa provide rich foraging opportunities for pelagic seabirds. They also support a pelagic longline fleet targeting tunas Thunnus spp. and swordfish Xiphias gladius, which set a total of 41.5 million (average 5.2 million per year) and 10.2 million hooks (average 1.3 million per year) respectively during the period 1998-2005. Fisheries observers collected seabird bycatch data from 2 256 sets (4.4 million hooks) and recorded a total of 1 954 birds killed during that period. In all, 11 species of seabird are confirmed incidentally caught by the fishery, eight of which are considered threatened. Birds were caught at an average rate of 0.44 per 1 000 hooks, resulting in an average of 2 900 seabirds killed per year, decreasing from approximately 5 900 in 1998 to 1 800 in 2005. Three techniques for extrapolating total seabird mortality were investigated and little difference between the estimates found. Generalised linear models were used to explain bycatch patterns and revealed that individual vessel is the most important explanatory variable, followed by vessel flag, moon phase, season, sea state, the use of a tori line, time of set, area and bathymetry. Estimates of the numbers of seabirds killed per year were lower than other studies, an improvement most likely linked to the termination of foreign bilateral agreements, as well as to improved awareness among fishers as a result of ongoing education campaigns. Some of the apparent decreases in catch rate could reflect reduced numbers of seabirds at sea, the result of ongoing population decreases in several key species.

Pelagic shark bycatch in the pelagic longline fishery off Southern Africa

Article

Full-text available

Apr 2009

Capture by pelagic longline fisheries has been identified as a key threat to turtle populations. This study is the first assessment of turtle bycatch in the South African pelagic longline fishery for tunas Thunnus spp. and swordfish Xiphias gladius. A total of 181 turtles was caught on observed sets between 1998 and 2005, at a rate of 0.04 per 1 000 hooks (0–15.5 per 1 000 hooks, SD = 1.28). Loggerhead turtles Caretta caretta comprised 60.0% of the total turtle capture and were caught at rate of 0.02 per 1 000 hooks. The second most commonly caught species was the leatherback turtle Dermochelys coriacea (33.8%), which were caught at rate of 0.01 per 1 000 hooks. Five hawksbill turtles Eretmochelys imbricata were caught at a rate of 0.001 per 1 000 hooks and three green turtles Chelonia mydas at a rate of 0.001 per 1 000 hooks. Catches were clustered, with 70% of turtles caught on 1% of sets. Apart from one set on the Agulhas Bank, on the southern coast of South Africa, all sets that caught three or more turtles were on the Walvis Ridge and on the shelf edge north of the Orange River (25°–31° S and 0°–15° E). Most of the variance in turtle bycatch was accounted for by 'vessel'. Five vessels (of a total of 50) caught 65% of turtles, at a rate of 0.4 per 1 000 hooks. The target species (swordfish or tunas) was the second most important explanatory variable; 89.5% of turtles were caught by swordfish-directed vessels at a rate of 0.15 per 1 000 hooks. Season was the third most important explanatory variable, with more turtles caught between January and June (0.13 per 1 000 per hooks) than in the remainder of the year (0.03 per 1 000 hooks), although leatherback turtles tended to be caught throughout the year. Extrapolations based on stratification by 5° grid cell, by season and by target species estimated that a total of 190 turtles was caught per year (approximately 100 loggerheads and 50 leatherbacks). Using three different techniques, the extrapolations varied between 190 and 560 turtles per year. However, if the proposed increase in fishing effort to 50 rights-holders is effected, turtle bycatch is likely to increase to about 770 turtles per year. Leatherback turtles caught by the South African pelagic longline fisheries are likely to be from the local nesting population. That population has been protected at its nesting beaches but has not recovered as expected. The overlap of turtle tracks and fishing effort suggests that the longline fishery could be partially responsible for the slow recovery.

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.

The estimated short-term discard mortality of a trawled elasmobranch, the spiny dogfish (Squalus acanthias)

Article

Feb 2007
FISH RES

To estimate the short-term bycatch discard mortality of otter trawl captured spiny dogfish (Squalus acanthias), individuals caught by a Northwest Atlantic commercial bottom-trawl vessel using 45–60min tows were held in held in pens for 72-h trials in lieu of being released. Mortality rates were compared to those in minimally stressed hook-and-line (control) dogfish subjected to the same protocols. To interpret physiological consequences of trawl capture, blood acid–base parameters were also assessed in dogfish following capture by both trawling and the hook-and-line control. Whole-blood pH (significantly depressed), pCO2 (significantly elevated) and pO2 (significantly depressed) were all markedly disturbed in trawled dogfish, indicating that trawl capture elicited a far greater disruption to vascular acid–base balance. However, 72h mortality was not negligible for control dogfish (24%) but similar to trawling (29%), indicating that pens likely caused the observed (72h) mortality associated with both capture methods. Still, in evaluating the range of 72h trawling mortalities found across pen trials, estimated tow-weight was a significant predictor of mortality, explaining 67% of the variation. This suggests that penning stress was merely an additive factor compounding initial capture stress that dictated the 72h mortality of trawled individuals. When normalized by subtracting out hook-and-line pen mortality, 72h trawling mortality generally remained well below the 50.0% spiny dogfish discard mortality rate currently estimated for trawling in the Northwest Atlantic and was even superceded by penning stress in lighter tows; a testament to the resiliency of this species. However, catch-weights exceeding 200kg yielded rapid elevations in 72h mortality that more closely approached current estimates. This intimates that as tows become more heavily packed, potentially fatal damage inflicted on this species can heighten quickly. Spiny dogfish discard mortality is thus postulated as more commensurate with current estimations for otter trawling when tows are heavily packed.

Effects of Capture by Trammel Net on Colorado River Native Fishes

Article

Full-text available

Jun 2012

Trammel nets are commonly used to sample rare fishes; however, little research has assessed delayed mortality associated with this capture technique. We conducted laboratory experiments to evaluate the effects of capture by trammel net on bonytail Gila elegans, razorback sucker Xyrauchen texanus, and roundtail chub Gila robusta, at 15, 20, and 25 degrees C. Fish (139-288 mm total length) were entangled in a trammel net for 2 h or captured by seine net and then monitored for mortality for at least 14 d. Blood samples were collected immediately after capture, and plasma cortisol levels were quantified as an index of capture-related stress. The cortisol response varied by species, but mean cortisol levels were higher for fish captured by trammel netting (295.9 ng/mL) relative to fish captured by seine netting (215.8 ng/mL). Only one fish (of 550) died during capture and handling, but 42% of the trammel-netted fish and 11% of the seine-netted fish died within 14 d after capture. In general, mortality after capture by trammel net increased with increased water temperature and at 25 degrees C was 88% for bonytail, 94% for razorback sucker, and 25% for roundtail chub. Delayed mortality of wild-caught fish captured by trammel net has the potential to be high, at least under some circumstances. We suggest that sampling frequency, timing of sampling (relative to reproductive cycles), and water temperature all be considered carefully when using trammel nets to sample diminished populations of imperiled native fishes.

Seabird bycatch in the demersal longline fishery off southern Africa

Article

Full-text available

Sep 2009

This study assesses seabird bycatch in the demersal longline hake (Merluccius capensis and M. paradoxus) fishery in the southern Benguela region. Observers collected seabird bycatch data from 2 412 sets (14 million hooks) in the South African fishery, accounting for 6.8% of total effort for the period 2000-2006. Of the 107 seabirds caught, at a rate of 0.008 per 1 000 hooks, 41 were killed (0.003 per 1 000 hooks). There was a significant decrease in catch rate, from 0.033 per 1 000 hooks in 2000 to 0.001 per 1 000 hooks in 2006. An estimated total of 225 (range 220-245) birds were killed per year by the South African fishery. Vessel, area and light conditions were all significant predictors of seabird bycatch. The white-chinned petrel Procellaria aequinoctialis was the species most commonly caught by the South African fleet, at a rate of 0.0027 per 1 000 hooks. From interviews with 13 observers and six members of the Namibian demersal longline fishery, seabird bycatch was estimated at 0.05 per 1 000 hooks and 0.13 per 1 000 hooks respectively. Observations were taken during four trips in Namibian waters in November 2006, in which 21 sets (456 000 hooks) were monitored. White-chinned petrels were killed at a rate of 0.14 per 1 000 hooks during these trips. Differences in catch rates between trips were investigated and moon phase, area and gear type were all found to be significant. All birds were caught using light gear, which sank significantly slower than heavier gear. The South African hake longline fishery has a relatively small impact on pelagic seabird populations compared with the Namibian fishery.

Understanding and Mitigating Vulnerable Bycatch in South African Trawl and Longline Fisheries

Article

Full-text available

Jan 2008

Interactions between seabirds and deep water hake trawl gear: an assessment of impacts in South African waters 2004/05

Article

Aug 2008
ANIM CONSERV

A simple model was developed to estimate seabird mortality across the fishery. Total fishing effort was estimated to be 60 000 trawls per year, based on 79 vessels fishing for 70% of the year and making on average three trawls per day (B. Rose, pers. comm.). Most trawls are conducted during daylight due to the vertical migration of hake. The first tow of the day thus seldom results in seabird interactions with the warp because no offal is discharged; these tows were excluded from warp interactions. Also excluded were four vessels with macerators (devices to finely chop discards, making them less attractive especially to large birds) as well as vessels that retain wastes to make fish meal, either on board (four freezer vessels) or returning it to land (eight wet fish boats on the last 3 days of their trips). This resulted in a total of c. 35 000 trawls with dumping taking place. Due to longer days in summer, effort was weighted 55% to summer trawls. Dumping was assumed to average 1 h per trawl, with total trawl duration averaging 3 h. These estimates are conservative; utilization of vessels averages above 70%, some dumping takes place from vessels with fish meal plants and macerators, and dumping lasted 1.2 h on average during our study trips. The effort data were used to calculate the total amount of time spent trawling in winter and summer both while dumping and not dumping, and this was used to extrapolate total mortality from the observed estimates of warp mortality. Mortality of birds entangled in nets can happen on any trawl, because it results from birds attempting to steal fish from the net. It is independent of dumping activity, and thus all trawl effort was included in the extrapolation of this mortality.

Use it or lose it? Sablefish, Anoplopoma fimbria, a species representing a fifth teleostean group where the NHE associated with the red blood cell adrenergic stress response has been secondarily lost

Article

May 2010
J EXP BIOL

Like most teleosts, sablefish (Anoplopoma fimbria Pallas 1814) blood exhibits a moderate Root effect (~35% maximal desaturation), where a reduction in blood pH dramatically reduces O(2) carrying capacity, a mechanism important for oxygenating the eye and filling the swim bladder (SB) in teleosts. Although sablefish lack a SB, we observed a well-defined choroid rete at the eye. The adrenergically mediated cell swelling typically associated with a functional red blood cell (RBC) beta-adrenergic Na(+)/H(+) exchanger (betaNHE), which would normally protect RBC pH, and thus O(2) transport, during a generalized acidosis, was not observed in sablefish blood. Neither isoproterenol (a beta-agonist) nor 8-bromo cAMP could elicit this response. Furthermore, RBC osmotic shrinkage, known to stimulate NHEs in general and betaNHE in other teleosts such as trout and flounder, resulted in no significant regulatory volume increase (RVI), further supporting the absence of a functional RBC betaNHE. The onset of the Root effect occurs at a much lower RBC pH (6.83-6.92) than in other teleosts, and thus RBC betaNHE may not be required to protect O(2) transport during a generalized acidosis in vivo. Phylogenetically, sablefish may represent a fifth group of teleosts exhibiting a secondary reduction or loss of betaNHE activity. However, sablefish have not lost the choroid rete at the eye (unlike in the other four groups), which may still function with the Root effect to oxygenate the retina, but the low pH onset of the Root effect may ensure haemoglobin (Hb)-O(2) binding is not compromised at the respiratory surface during a general acidosis in the absence of RBC betaNHE. The sablefish may represent an anomaly within the framework of Root effect evolution, in that they possess a moderate Root effect and a choroid rete at the eye, but lack the RBC betaNHE and the SB system.

Biology of adult sablefish, Anoplopoma fimbria, in waters off western Canada

Conference Paper

Full-text available

Jan 1983

Demers, N.E. and Bayne, C.J. 1997. The immediate effects of stress on hormones and plasma lysozyme in rainbow trout. Developmental and Comparative Immunology. 21:363-373.

Article

Full-text available

Jul 1997
DEV COMP IMMUNOL

q Abstract-The fight-or-flight response prepares an animal for coping with alarming situations and their potential consequences, which include injury. The possible involvement of innate components of immunity in the response has received little attention. We determined plasma concentrations of stress hormones and lysozyme activity before and after a 10 min handling stressor. Rainbow trout (Oncorhynchus mykiss) were anesthe-tized in their home tanks, bled, revived, and then stressed by being held in the air in a net for 30 s and placed in a shallow bucket of water for 10 min. Fish were then captured, concussed (in one of two experiments) and bled again. Control fish were also bled twice, but were kept anesthetized in their holding tanks between bleedings. Following the stres-sor, plasma cortisol, adrenaline and lysozyme activity were significantly increased. The experiment was repeated 4 months later with a similar outcome. While chronic stress is eventually immunosuppressive, acute stress/ trauma may help enhance both cellular and humoral components of innate defenses at times of likely need. 0 1997 Elsevier Science Ltd. q

Evaluating Bycatch: A National Approach to Standardized Bycatch Monitoring Programs

Technical Report

Full-text available

Oct 2004

On March 6, 2003, the National Marine Fisheries Service (NMFS) issued a National Bycatch Strategy to address issues related to the management of bycatch within the Nation’s fisheries. One component of that strategy was the establishment of a National Working Group on Bycatch (NWGB) to develop a national approach to standardized bycatch reporting methodologies and monitoring programs. This work is to be the basis for regional teams (also established in the National Bycatch Strategy) to make fishery-specific recommendations. The NWGB reviewed regional issues related to fisheries and bycatch and discussed advantages and disadvantages of various methods for estimating bycatch, including: (1) fishery-independent surveys; (2) self-reporting through logbooks, trip reports, dealer reports, port sampling, and recreational surveys; (3) at-sea observation, including observers, digital video cameras, digital observers, and alternative platform and remote monitoring; and (4) stranding networks. All of the methods may contribute to useful bycatch estimation programs, but at-sea observation (observers or electronic monitoring) provides the best mechanism to obtain reliable and accurate bycatch estimates for many fisheries. Often, observer programs also will be the most cost-effective of these alternatives. At-sea sampling designs should be formulated to achieve precision goals for the least amount of observation effort, while also striving to increase accuracy. This is done through random sample selection, by developing appropriate sampling strata and sampling allocation procedures and by implementing appropriate tests for bias. These designs and tests are needed for each fishery. Sampling programs will be driven by the precision and accuracy required by managers to address management needs: for estimating management quantities such as allowable catches through a stock assessment, for evaluating bycatch relative to a management standard such as allowable take and for developing mitigation mechanisms. The recommended precision goals for estimates of bycatch are defined in terms of the coefficient of variation (CV) of each estimate. Eighty-four fisheries were evaluated for bycatch monitoring and classified into one of five categories (None, Baseline, Pilot, Developing, or Mature). Additionally all of these fisheries were rated as to their vulnerability (High, Moderate or Low) to bycatch of three types of resources: (1) fishery resources (excluding protected species); (2) marine mammals; and (3) other protected species, that is, ESA-listed species (excluding marine mammals), other sea turtles and other seabirds. Of the 84 fisheries, 5% have a Mature observer program, 20% were Developing (25% were either Mature or Developing), 10% have a Pilot program, 29% have a Baseline program and 37% do not have a program (None). (Note that the percentages sum to 101 due to rounding.) Thirty-one percent of these 84 fisheries are rated High for bycatch vulnerability of one or more of the three resource types (thus, 69% are rated Moderate or Low for all three types of resources); 6% of these fisheries are both rated High for bycatch vulnerability of one or more of the three resource types and recommended for establishment of Baseline or Pilot observer programs. A strategy for bycatch monitoring was developed based upon the vulnerability of a fishery, the adequacy of current monitoring programs and sampling cost estimates.

Young of the Year Sablefish Abundance, Growth, and Diet in the Gulf of Alaska

Article

Full-text available

Jan 2001

Bycatch Management and the Economics of Discarding

Article

Full-text available

Jan 1997

Sean Pascoe

The increase in commercial fisheries production over the last 50 years has been accompanied by an increase in the level of incidental catch and discarding of a number of species. Approximately one quarter of the marine commercial catch destined for human consumption is discarded at sea. This has raised concerns by a number of groups in society, including environmentalists, humanitarians and fishers themselves. In this paper, the economic incentives to discard fish are examined. The effects of different management policies on these incentives are also investigated. The concept of an optimal level of discarding is discussed taking into account the externalities that can be created by discarding. Finally, the effectiveness of various measures to reduce the level of discarding is reviewed. These including technical, administrative and economic measures.

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.

Estimating von Bertalanffy growth parameters of sablefish Anoplopoma fimbria and Pacific cod Gadus macrocephalus using tag-recapture data

Article

Full-text available

Jan 1993
FISH B-NOAA

Recent papers have provided new insights into the prob lem of estimating von Bertalanffy growth parameters from tag recapture data. In particular, the in consistency and bias of Fabens' (1965) esti~ates appear to have been addressed by James (1991l. Using simulation. we examine the pattern of bias associated with different er ror assumptions for Fabens' esti mates, weighted Fabens' estimates proposed by James. and a robust method also proposed by James. Our results corroborate James' finding that his robust estimates can be sig nificantly less biased than other methods. We then apply these esti mators to tag-recapture data ob tained for sablefish Anoplopomafim bria found in the Gulf ofAlaska and off the U.S. west coast. and Pacific cod Gadus macrocephalus found in the eastern Bering Sea. These spe cies are difficult to directly age. so tag-recapture data provide welcomed independent estimates of growth pa rameters and an indirect method of validating age-determination crite ria. The von Bertalanffy parameter estimates using tag-recapture data and James' method were most simi lar to estimates calculated directly from length-at-age data.

Climatic Influence Linking Copepod Production with Strong Year-Classes in Sablefish, Anoplopoma fimbria

Article

Full-text available

Apr 1992
CAN J FISH AQUAT SCI

Stomach contents from first-feeding larval sablefish (Anoplopoma fimbria) comprised mainly calanoid copepods. Along the west coast of Vancouver Island, these copepods were the dominant zooplankton at the depth that sablefish larvae developed. We propose that strong year-classes in sablefish populations occur when there is exceptional production of copepods. The periods of exceptional copepod production appear to be correlated with climate and ocean conditions.

Allostasis: A New Paradigm to Explain Arousal Pathology

Article

Full-text available

Jan 1988

homeostasis versus allostasis mechanisms of allostasis allostatic regulation of the immune response regulation of arousal pathology from chronic arousal definitions of health and approaches to therapeutics hypertension / psychoneuriommunology / iatrogenesis / health (PsycINFO Database Record (c) 2012 APA, all rights reserved)

Stress and the immune system

Article

Full-text available

May 2003
Pathophysiology

Stephen Pruett

Stressors can positively or adversely affect immune and inflammatory responses. However, the current understanding of these effects at the cellular and molecular levels is not sufficient to allow prediction of the effects of a particular stressor on a particular immune or inflammatory function. Three complementary conceptual frameworks are presented that may prove useful in developing such an understanding. In addition, specific examples of the action of particular stress mediators on particular immune or inflammatory end points are discussed, and the relationship of these observations to the conceptual frameworks is indicated. Several of the effects discussed are relevant clinically, and the prospects for pharmacological intervention to prevent adverse effects of stressors on the immune system are discussed. Finally, some of the factors that can (sometimes unexpectedly) influence the outcome of stress-immunology studies and some of the pitfalls that continue to make this area of research controversial in some circles are discussed.

Accumulation and long-term effects of stress in fish.

Chapter

Jun 2000

C. B. Schreck

This book brings together a range of scientific perspectives from biomedical research on stress and welfare, and assesses new approaches to conceptualizing and alleviating stress. While much of the focus in on conventional farm animals, there is also consideration of fishes, laboratory animals and zoo animals. The 30 contributors include leading authorities from North America, Europe, New Zealand and Australia. This book is invaluable for advanced students and researchers in animal behaviour, animal welfare, animal production, veterinary medicine and applied psychology. For more information see the CABI Publishing online bookshop (http://www.cabi.org/Bookshop/).

The pituitary‐interrenal axis as an indicator of stress in fish

Article

Jan 1981

E.M. Donaldson

Suppression by cortisol of the mitogen‐indueed proliferation of peripheral blood leucocytes from plaice, Pleuronectes platessa L‐

Article

Dec 1985

A.S. Grimm

This chapter presents an investigation of the effect of cortisol on the mitogen-induced proliferation of peripheral blood leucocytes of plaice. Outbreaks of disease in fishes are frequently associated with environmental stressors, although a causal relationship between stressors and disease is less often established. As stressors commonly, but not universally, cause increased activity in the hypothalamo-pituitary-adrenocortical system, it has been proposed that corticosteroids are important mediators of the stressor's action. Treatment of fish with cortisol can cause increased incidence of disease, although it is questionable whether the plasma levels of steroid were physiological. The disease-related action of corticosteroids in mammals almost certainly includes immunosuppressive mechanisms such as macrophage inhibition, sequestration of lymphocytes, and inhibition of lymphocyte function. The fact that physiological levels are suppressive in vitro suggests that cortisol may function similarly in vivo. This steroid action may be a significant part of the mechanism by which stressors induce disease.

Bidirectional effects of stress and glucocorticoid hormones on immune function: Possible explanations for paradoxical observations

Article

Jan 2001

Methods for determining the tolerance of fishes to environmental stressors

Article

Jan 1981

Biology of adult sablefish (Anoplopoma fimbria) in waters off western Canada

Article

Jan 1983

Accumulation and long-term effects of stress in fish

Article

Jan 2000

Stress and compensation in teleostean fishes: Response to social and physical factors

Article

Jan 1981

C.B. Schreck

Stress and the Individual

Article

Sep 1993
ARCH INTERN MED

Bruce S Mcewen

Objective: This article presents a new formulation of the relationship between stress and the processes leading to disease. It emphasizes the hidden cost of chronic stress to the body over long time periods, which act as a predisposing factor for the effects of acute, stressful life events. It also presents a model showing how individual differences in the susceptibility to stress are tied to individual behavioral responses to environmental challenges that are coupled to physiologic and pathophysiologic responses.Data Sources: Published original articles from human and animal studies and selected reviews. Literature was surveyed using MEDLINE.Data Extraction: Independent extraction and cross-referencing by us.Data Synthesis: Stress is frequently seen as a significant contributor to disease, and clinical evidence is mounting for specific effects of stress on immune and cardiovascular systems. Yet, until recently, aspects of stress that precipitate disease have been obscure. The concept of homeostasis has failed to help us understand the hidden toll of chronic stress on the body. Rather than maintaining constancy, the physiologic systems within the body fluctuate to meet demands from external forces, a state termed allostasis. In this article, we extend the concept of allostasis over the dimension of time and we define allostatic load as the cost of chronic exposure to fluctuating or heightened neural or neuroendocrine response resulting from repeated or chronic environmental challenge that an individual reacts to as being particularly stressful.Conclusions: This new formulation emphasizes the cascading relationships, beginning early in life, between environmental factors and genetic predispositions that lead to large individual differences in susceptibility to stress and, in some cases, to disease. There are now empirical studies based on this formulation, as well as new insights into mechanisms involving specific changes in neural, neuroendocrine, and immune systems. The practical implications of this formulation for clinical practice and further research are discussed.(Arch Intern Med. 1993;153:2093-2101)

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.

Modifications to reduce bycatch in prawn trawls: A review and framework for development

Article

Mar 2000
REV FISH BIOL FISHER

Matt Kenyon Broadhurst

The incidental capture of non-target species from prawn trawling has recently attracted worldwide attention. Primarily, concerns arise from the perception that prawn trawls catch and discard large numbers of juveniles of species that, when larger, are targeted in other commercial and recreational fisheries. While several management options are available, the majority of fisheries in the world have attempted to address this issue through physical modifications to trawls, designed to improve selectivity. The types of modifications used reflect fishery-specific characteristics; however, most can be broadly classified into two categories, including: (1) those that separate species by differences in behaviour; and (2) those that mechanically exclude unwanted organisms according to their size. In the present paper, I provide a chronological review of publications in the primary literature that describe experiments examining modifications within these categories. This review shows that inherent variabilities among different fisheries greatly influence the types of designs that need to be applied and although some designs have the potential for application across different fisheries, significant modification and re-evaluation are often required. By collating information from previous studies, I also propose a framework encompassing the various stages involved in developing and applying successful modifications in prawn-trawl fisheries. The key stages identified include: (1) quantification of bycatches and accumulation of fishery-related information; (2) examination and re-evaluation of modifications; (3) assessment of damage inflicted on escaping individuals; and (4) promotion of recommended designs.

Preface1

Article

Nov 2002
J CONTAM HYDROL

In Vitro addition of vitamin-C affects rainbow trout lymphocyte responses

Article

May 1993

Proliferation and macrophage activating factor (MAF) secretion responses from vitamin C depleted rainbow trout were increased by the presence of exogenous vitamin C in the culture. In addition, parenteral addition of vitamin C enhanced proliferation in leucocytes from vitamin C depleted trout, and supplementation of this vitamin in culture stimulated proliferation responses of leucocytes from trout fed a commercial diet. Possible mechanisms by which vitamin C may influence lymphocyte responses in culture are discussed and include overcoming the inhibitory effects of cortisol or histamine.

Behavior of juvenile sablefish, Anoplopoma fimbria (Pallas), in a thermal gradient

Article

Apr 1998
J EXP MAR BIOL ECOL

The vertical distribution of early juvenile sablefish, Anoplopoma fimbria (Pallas), and their behavioral responses to changing food and temperature conditions were examined in laboratory experiments. Although field collections have suggested that juveniles are obligate residents of the neuston, laboratory experiments on diel movements indicated the potential for downward movement during the day, when activity levels were high and active foraging would be likely. The relationship of downward movement to fish size (small vs. large juveniles), prior feeding success (high vs. low rations) and thermal structure of the water column (isothermal vs. varying intensities of thermal stratification) were tested. Thermal stratification inhibited downward movement, with sablefish displaying clear avoidance of cold water even when the thermal gradient was moderate (12 °C top layer and 8 °C bottom layer). However, sablefish could be induced to swim downward into cold water if food was introduced beneath the thermocline. Across all temperature treatments, occurrence in cold water significantly increased when food was present. Increasing the sharpness of the thermal gradient (top layer=12 °C, bottom layer=8, 6, 4 or 2 °C) did not affect the percentage of time spent in cold water, but did shorten the maximum time an individual would spend beneath the thermocline. Movement into cold water constituted a potentially lethal risk for juvenile sablefish; dives beneath the thermocline that exceeded 60 s resulted in loss of equilibrium and immediate death for small fish moving from 12 to 2 °C water. Thus, sablefish displayed behavioral trade-offs between food acquisition and the physiological risk of cold temperatures, similar to previous studies documenting balancing of foraging behavior and predation risk. Behavioral responses to thermal stratification were modified by fish size and hunger level, with larger juveniles and those held on low rations spending more time in cold water. These behavioral responses correspond with the high feeding requirements necessary to maintain the naturally rapid growth rates of this species and the transitions in habitat associated with different life history stages.

An Effective Culture System for Studying in Vitro Mitogenic Responses of Channel Catfish Lymphocytes

Article

Sep 1983

Lymphocytes of channel catfish Ictalurus punctatus can be stimulated by lipopolysaccharide (LPS) and concanavalin A (ConA) to synthesize deoxyribonucleic acid (DNA) in vitro. The importance of the proper serum supplement and tonicity of the culture medium was established empirically. Responses to LPS were temperature-independent whereas the responses to ConA were suppressed at lower temperatures. Although peripheral blood and splenic lymphocytes exhibited similar responses to both mitogens, anterior kidney cells did not respond, probably due to the high background levels of DNA synthesis in this highly hematopoietic organ.Received September 27, 1982 Accepted June 12, 1983

8 Immunomodulation: Endogenous Factors

Article

Dec 1997
Fish Physiol

Carl B Schreck

This chapter examines the different aspects of immunomodulation in the fish. The general health of fish is a function of their environment, the nature of pathogens, and factors intrinsic to the fish themselves. Circulating levels of leukocytes change through time when fish are stressed. Changes following physical types of stressors include depression in the number of lymphocytes in the circulation, or the number of these cells relative to the number of erythrocytes. Negative effects of stress on disease resistance appear to be because of the depression of antibody-synthesizing capability through effects on lymphocytes. Stress effects on the immune system of fish may be mediated by the endocrine system. Catecholamines and corticosteroids are the major stress hormones of vertebrates. Some species of teleosts do not fit the general paradigm for the endocrine stress response, the extremely rapid secretion of catecholamines and rapid secretion of cortisol following the onset of stress. The mechanism of buffering in rainbow trout can be attributed to the elevation in the concentration of corticosteroid-binding globulin as spawning approaches. The globulin reduces the amount of free cortisol that could pass into the ovarian fluid and, subsequently, the egg.

Impact of oxygen deficiency on the disease status of common dab Limanda limanda

Article

Jan 1995

An epidemiological survey of the fish diseases lymphocystis, epidermal papilloma and skin ulcers in common dab Limanda limanda L. was conducted in the southern Kattegat each year in May from 1984 to 1993. During the period of investigation, severe oxygen depletion occurred in late summer 1986 and 1988. After the oxygen deficiency in 1986, the occurrence of lymphocystis and epidermal papilloma increased and peaked in 1989 with prevalences of 14.7 and 3.3%, respectively. The prevalence of skin ulcers never exceeded 0.6%. The relative risk of contracting lymphocystis increased significantly from 1987 to 1991 compared with 1984 to 1986, the period prior to the severe oxygen depletion. A significant increase in the relative risk of contracting epidermal papilloma was observed from 1987 to 1990. Females were 3 times more likely to contract this disease than males. The relative risk of skin ulcers did not change significantly during the investigation period. The prevalence of lymphocystis and epidermal papilloma was negatively correlated with the minimum oxygen levels measured in August and September the previous year; this negative correlation was significant (p < 0.05) for lymphocystis in September, while not for epidermal papilloma (p < 0.1). The prevalence of lymphocystis and epidermal papilloma was significantly correlated (p < 0.01). No significant correlation was observed between stock density (expressed as catch per unit effort) and the diseases in question. It is probably the stress caused by the oxygen deficiency - especially the sublethal levels - that triggered the outbreak of the 2 viral diseases lymphocystis and epidermal papilloma.

Proliferative Response of English Sole Splenic Leukocytes to Mitogens

Article

Mar 1994

The mitogenic response and mixed leukocyte reaction (MLR) were studied to determine the ability of a benthic marine fish, English sole Pleuronectes vetulus, to produce leukoproliferative (LP) responses. The mitogenic response of English sole leukocytes was assessed for a variety of mitogens. In vitro culture conditions for English sole leukocytes that would maintain cellular viability and allow leukocytes to proliferate were initially determined with an undefined medium. Factors that were varied to create an effective mitogen assay included mitogen type (pokeweed mitogen, concanavalin A, phytohemagglutinin, and lipopolysaccharide), mitogen concentrations, incubation time and temperature, medium supplementation, and number of leukocytes per culture. A leukocyte concentration of 1 × 10⁷ leukocytes/mL provided for the greatest proliferation; cell concentrations above or below this level resulted in less proliferation. A higher degree of proliferation occurred when the leukocytes were incubated with fetal calf serum than with heatinactivated autologous plasma. It was confirmed that leukocytes were responsible for proliferation of the Splenic whole-cell population in response to mitogens. Pokeweed mitogen and lipopolysaccharide were able to stimulate English sole leukocytes to proliferate at ITC. However, phytohemagglutinin and concanavalin A were generally unable to induce cellular proliferation. The ability of pooled leukocytes to produce a tridirectional MLR was also examined once effective culture conditions were determined via the mitogen assay. Mixed leukocyte reactions were negative or borderline positive when leukocytes from three English soles were cultured.

Multiple Acute Disturbances Evoke Cumulative Physiological Stress Responses in Juvenile Chinook Salmon

Article

Mar 1986

The corticosteroid and hyperglycemic stress responses to multiple acute disturbances were cumulative in juvenile chinook salmon Oncorhynchus tshawytscha. This was demonstrated by the stepwise pattern of increased plasma cortisol and glucose concentrations in fish subjected to a 30-s handling stress applied repeatedly at 3-h intervals over 6 h. The accumulation of physiological stress responses was substantiated by the resultant combined effects of these repeated disturbances on changes in concentrations of plasma lactate and of ionic sodium and potassium, and on the rate of decline of hepatic glycogen concentrations, all of which were greater than those that followed a single handling. Healthy fish appeared more able than diseased fish to elevate plasma cortisol after each of the three successive disturbances, but plasma glucose concentrations following the repeated handlings were higher in the unhealthy fish. As judged from plasma cortisol and glucose responses in fish subjected to a single 30-s stress at four different times in the day, there was little diurnal difference in sensitivity or responsiveness to handling.

Mitogen induced in vitro stimulation of lymphoid cells from organs of sea bass ( Dicentrarchus labrax L.)

Article

Apr 1999

A serum-free culture medium for channel catfish in vitro immune responses

Article

Apr 1991

This paper describes a chemically defined serum-free medium which supports channel catfish (Ictalurus punctatus) lymphocyte mitogen responses to both LPS and ConA as well as proliferation in mixed lymphocyte reactions. Furthermore, this medium has been successfully used to support catfish antibody production in primary and secondary in vitro responses to both thymus independent and thymus dependent antigens. The medium, designated ‘A-L’, is an isotonic 1:1 mixture of two commercially available media, AIM-V and Leibovitz's L-15. Although the essential nutrients contained in this serum-free medium have not yet been identified, it appears that D(+) galactose is an important ingredient for catfish T cell proliferation. This serum-free culture system will permit investigations into new areas of channel catfish immune regulation.

Key principles for understanding bycatch discard mortality

Article

Nov 2002
CAN J FISH AQUAT SCI

Michael W. Davis

Physiological changes in fish from stress in aquaculture with emphasis on the response and effects of corticosteroids

Article

Jan 1991
Annu Rev Fish Dis

Stress in fish caused by physical disturbances encountered in aquaculture, such as handling and transport, evokes a variety of responses that may be adaptive or maladaptive. The overall effect of stress may be considered as a change in biological condition beyond the normal resting state that challenges homeostasis and, thus, presents a threat to the fish's health. These stress-induced changes are grouped as primary; secondary, which includes metabolic, hematological, hydromineral, and structural; and tertiary or ‘whole animal’ responses. Many of these responses can be used as quantitative indicators of stress although investigators need to be aware of the various ‘nonstress’ factors that can also influence these conditions. A major focus of current research is on the response of the hypothalamic-pituitary-interrenal axis and the resultant elevation of circulating corticosteroids. Stress, through the action of corticosteroids, may (a) reduce immunocompetence by influencing lymphocyte numbers and antibody-production capacity, and (b) affect reproduction by altering levels and patterns of reproductive hormones that influence maturation. Stress may also alter metabolic scope in fish and affect growth, partly as a result of the catabolic or gluconeogenic effect of corticosteroids. Although certain stressors encountered during normal aquacultural procedures may be unavoidable, a number of practical approaches are suggested that would help to alleviate the detrimental effects of stress in fish.

A serum-reduced culture medium for carp lymphocyte in vitro mitogen-induced proliferation

Article

Jan 1995

Status and use of biological indicators for evaluating the effects of stress on fish

Article

Jan 1990

S.M. Adams

Laboratory bioassays and other conventional methods of assessing stress on aquatic organisms generally lack ecological realism because of the many environmental factors that can influence stress responses at all levels of biological organization. The biological indicator approach involves measurement of a suite of selected stress responses at several levels of biological organization to assess sublethal stress effects on fish, to give early warning of stress, and to obtain insights into causal relationships between stressors and effects manifested at higher levels of biological organization. The types of stress responses measured range from those at the subcellular and biochemical levels to those at the ecosystem level; the responses segregate along gradients of toxicological and ecological relevance and of response time.

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 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.

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.

Temperature magnified postcapture mortality in adult sablefish after simulated trawling

Article

Apr 2005
J FISH BIOL

For sablefish Anoplopoma fimbria that had been transferred abruptly from ambient (5·7° C) to temperatures ranging from 15 to 20° C for 30 min followed by 15 min in air (19·5) C), mortality increased with temperature. Mortality occurred at lower temperatures for sablefish that were net-towed for 4 h at ambient temperature before exposure to a rapid increase in temperature. A clear relationship was apparent between serum lactate and temperature with lactate increasing as temperature increased. For treatments in which mortality did not occur, lactate decreased sharply within 24 h, suggesting recovery. It would appear that the critical postcapture temperature for sablefish that reside and are captured at 4-6° C, would be between 12 and 15° C. The results of this study suggest that fishery management strategies designed to increase postcapture survival of sablefish bycatch should include a consideration of the impact of exposure to seasonal thermoclines and seasonally elevated air temperatures.

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

Article

Jan 2005
J FISH BIOL

Capture-Related Stressors Impair Immune System Function in Sablefish

Abstract

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