Injuries from non-retention in gillnet fisheries suppress reproductive maturation in escaped fish

Influence of marine habitat on microplastic prevalence in forage fish and salmon in the Salish Sea

Microplastics are increasingly prevalent in marine systems and are a growing concern as a marine pollutant and contaminant with consequences for high trophic level consumers, including humans. Given evidence that links plastics to degraded ecosystem functioning and organismal health, there is increased interest in understanding the prevalence, fate and consequences of marine plastics. Microplastics contain and absorb harmful chemicals which may serve as endocrine disruptors and have negative implications for growth, reproductive health, and longevity. To expand current knowledge on microplastics in coastal marine ecosystems and the potential for biomagnification in marine food webs, we conducted stomach analyses of microplastics in Pacific salmon (Oncorhynchus spp.) and Pacific sand lance (Ammodytes personatus), an important prey for salmon. Prevalence of microplastics was substantial; 77 % of all salmon and 25 % of all sand lance stomachs contained at least one microplastic. Fish were sampled at multiple sites throughout the inland Salish Sea, including beaches and sediment bedforms for Pacific sand lance and open-water pelagic habitat for Pacific salmon. Pacific sand lance sampled at beach sites had more microplastics compared to those sampled in subtidal sediments and there were more plastics in sand lance at a protected beach site as compared to an exposed beach site. Prevalence of plastics in salmon differed according to species and included analyses of pink salmon (Oncorhynchus gorbuscha), Chinook (Oncorhynchus tshawytscha), and Coho salmon (Oncorhynchus kisutch); plastics were predominantly fibers in all species, though there were relatively higher rates of ingestion of films and particles in Chinook. Comparisons between plastic concentrations and stomach fullness indicated a slight negative trend, suggesting that plastics may be retained. Further investigation is needed to develop a more thorough understanding of the prevalence and fate of microplastics in coastal marine systems such as the Salish Sea, their concentration within marine food webs, and the implications for species targeted in fisheries.

Host-pathogen-environment interactions predict survival outcomes of adult sockeye salmon (Oncorhynchus nerka) released from fisheries

Incorporating host-pathogen(s)-environment axes into management and conservation planning is critical to preserving species in a warming climate. However, the role pathogens play in host stress resilience remains largely unexplored in wild animal populations. We experimentally characterized how independent and cumulative stressors (fisheries handling, high water temperature) and natural infections affected the health and longevity of released wild adult sockeye salmon (Oncorhynchus nerka) in British Columbia, Canada. Returning adults were collected before and after entering the Fraser River, yielding marine- and river-collected groups, respectively (N = 185). Fish were exposed to a mild (seine) or severe (gill net) fishery treatment at collection, and then held in flow-through freshwater tanks for up to four weeks at historical (14°C) or projected migration temperatures (18°C). Using weekly nonlethal gill biopsies and high-throughput qPCR, we quantified loads of up to 46 pathogens with host stress and immune gene expression. Marine-collected fish had less severe infections than river-collected fish, a short migration distance (100 km, 5-7 days) that produced profound infection differences. At 14°C, river-collected fish survived 1-2 weeks less than marine-collected fish. All fish held at 18°C died within 4 weeks unless they experienced minimal handling. Gene expression correlated with infections in river-collected fish, while marine-collected fish were more stressor-responsive. Cumulative stressors were detrimental regardless of infections or collection location, probably due to extreme physiological disturbance. Because river-derived infections correlated with single stressor responses, river entry probably decreases stressor resilience of adult salmon by altering both physiology and pathogen burdens, which redirect host responses toward disease resistance.

Controlled experiments to explore the use of a multi-tissue approach to characterizing stress in wild-caught Pacific halibut (Hippoglossus stenolepis)

The integration of multiple tissues in physiological and ecological analyses can enhance methodological approaches, increase applications for data and extend interpretation of results. Previous investigations of the stress response in fish have focused primarily on cortisol levels in a single matrix-blood plasma-which confines interpretations of cortisol levels to a short temporal frame. Epidermal mucus has been proposed as an alternative or complement to plasma that may provide a view to cortisol levels over a different temporal window allowing comparative assessment. Here, we explore the potential for multi-tissue cortisol analysis using both plasma and epidermal mucus in Pacific halibut (Hippoglossus stenolepis). The relative timing at which cortisol increased and decreased in the two matrices as well as cortisol concentrations at estimated peak levels were compared in two trials after (i) inducing cortisol synthesis by adrenocorticotropic hormone (ACTH_1-24) administration and (ii) inducing cortisol elimination using cortisol (hydrocortisone, 98%) injection. The ACTH treatment elicited a peak plasma cortisol response approximately 12 hours post-injection, while mucus cortisol concentrations peaked later at approximately 62 hours post-injection. Exogenous cortisol treatments suggested relatively little transfer of cortisol from plasma to mucus, potentially reflecting differential effects of endogenous and exogenous cortisol. Our results suggest the potential utility of mucus as a sampling matrix that provides an extended window for detection of the stress response as compared to plasma. Results also suggest the utility of a multi-tissue approach to cortisol analysis with potential applications to applied fisheries research. Increased understanding of the relative scale of the cortisol response to stress (e.g. capture) will allow researchers and managers to better interpret the physiological condition and survival outcome of fish subjected to regulatory discard.

The impact of injury on apparent survival of whale sharks (Rhincodon typus) in South Ari Atoll Marine Protected Area, Maldives

The whale shark (Rhincodon typus) is an endangered species with a declining global population. The South Ari Atoll Marine Protected Area (SAMPA), Maldives, is one of few locations globally where year-long residency of individuals occurs. This SAMPA aggregation appears to consist almost exclusively of immature males. Due to its year-round residency, this local aggregation is subjected to a high degree of tourism pressure. This ecotourism contributes to the high level of interest and protection offered to whale sharks by the local community. Unfortunately, if regulations are not followed or enforced, tourism can bring with it major stressors, such as accidental injuries. We used POPAN capture-mark-recapture models and lagged identification rate analysis to assess the effect of major injuries on whale shark residency within SAMPA. Injuries may be obtained outside SAMPA. We found individuals with major injuries had a higher apparent survival in the area than those without. Lagged identification rates also demonstrated that sharks with major injuries are more likely to return to the area. We suggest that major injuries result in sharks prolonging their time in the developmental habitat. These findings have implications for individual fitness and the population viability of this endangered species. We propose targeted conservation strategies be considered to protect sharks from further injury. Based on the presented spatio-temporal distributions of sharks, and current local knowledge of sighting patterns, speed limit zones and propeller-exclusion zones should be implemented and enforced. If carried out alongside tourist education, these measures will contribute to the protection of whale sharks within SAMPA and beyond. Furthermore, our results can aid research direction, alongside regulation and enforcement development, at similar sites worldwide.

Dermatophytosis in companion animals: A review

Dermatophytosis, a zoonotic disease, is caused by fungi of three main genera, namely, Micropsorum, Trichophyton, and Epidermophyton. Specific lesions of dermatophyte infections are localized in the face, legs, and/or tail. Skin lesions in infected animals demonstrate localized alopecia, erythema, and crust, which are more commonly known as ringworm. Factors that affect dermatophytosis include the dermatophyte species; virulence factors of the agent; and the immune status, age, and sex of the host. High levels of cortisol and pro-inflammatory cytokines have also been reported to play an important role in dermatophyte infection. This review aims to explore and understand factors that affect dermatophyte infection with an emphasis on the prevalence, clinical signs, pathogenesis, immune response, and the roles of cortisol and cytokines in companion animals infected by a dermatophyte.

Handling, infectious agents and physiological condition influence survival and post-release behaviour in migratory adult coho salmon after experimental displacement

For Pacific salmon captured and released by fisheries, post-release behaviour and survival may be influenced by their health and condition at time of capture. We sought to characterize the interactions between infectious agent burden, fish immune and stress physiology and fisheries stressors to investigate the potential for capture-mediated pathogen-induced mortality in adult coho salmon Oncorhynchus kisutch. We used radio-telemetry paired with high-throughput qPCR of non-lethal gill biopsies for infectious agents and host biomarkers from 200 tagged fish experimentally displaced and exposed to various experimental fisheries treatments (gill net entanglement, recreational angling and recreational angling with air exposure vs. non-sampled control). We characterized relationships among post-release behaviour and survival, infectious agent presence and loads, physiological parameters and transcription profiles of stress and immune genes. All infectious agents detected were endemic and in loads consistent with previous adult Pacific salmon monitoring. Individuals exposed to fisheries treatments were less likely to reach spawning habitat compared to controls, and handling duration independent of fisheries gear had a negative effect on survival. High infectious agent burden was associated with accelerated migration initiation post-release, revealing behavioural plasticity in response to deteriorating condition in this semelparous species. Prevalence and load of infectious agents increased post-migration as well as transcription signatures reflected changes in immune and stress profiles consistent with senescence. Results from this study further our understanding of factors associated with fisheries that increase risk of post-release mortality and characterize some physiological mechanisms that underpin migratory behaviour.

Cumulative Effects of Thermal and Fisheries Stressors Reveal Sex-Specific Effects on Infection Development and Early Mortality of Adult Coho Salmon (Oncorhynchus kisutch)

Multiple stressors are commonly encountered by wild animals, but their cumulative effects are poorly understood, especially regarding infection development. We conducted a holding study with repeated gill and blood sampling to characterize the effects of cumulative stressors on infection development in adult coho salmon. Treatments included chronic thermal stress (15°C vs. 10°C) and acute gill net entanglement with an air exposure (simulating fisheries bycatch release). The potential loadings of 35 infectious agents and the expression of 17 host immune genes were quantified using high-throughput quantitative polymerase chain reaction, while host physiology was characterized with chemical analysis of blood. Temporal increases in infectious agent richness and loads were concurrent with decreased expression of immune genes in fish sampled in the river. In the laboratory, mortality was minimal in cool water regardless of fishery treatment (<15%). Elevated water temperature under laboratory conditions increased mortality of males and females (8% and 28% mortality, respectively, delayed by >1 wk) and enhanced mortality associated with handling and biopsy (∼40% both sexes). Experimental gillnetting at high temperature further enhanced female mortality (73%). Fish held at high temperature demonstrated heavier infectious agent loads, osmoregulatory impairment, suppressed female maturation, and upregulation of inflammatory and extracellular immune genes. At high temperature, heavy Parvicapsula minibicornis loads were associated with premature mortality. Females exhibited physiological impairment from both stressors after 1 wk, and infection burdens correlated poorly with immune gene regulation compared with males. Cumulative effects of multiple stressors on female mortality are likely a function of physiological impairment and enhanced infections at high temperature.

Dermal injuries caused by purse seine capture result in lasting physiological disturbances in coho salmon

Fish vitality can be measured by classifying reflex impairments (i.e., a visual impression of the ability to respond to induced stimuli) and visible injuries. These metrics can predict survival probability following release from fisheries, and monitoring physiological disturbances following capture can help understand mechanisms of mortality. To test the hypothesis that severity of injury and reflex impairment influences the time course of physiological recovery, coho salmon (Oncorhynchus kisutch) were held for up to 84-h following capture by purse seine. We classified reflex impairments and visible dermal injuries, and through repeated blood sampling, assessed metrics indicative of stress, exhaustion, and osmoregulatory disturbances. Reflex-impairments and blood lactate levels suggested fish were exhausted upon capture but recovered after 48 h. Conversely, fish with dermal injuries showed disruptions to ion homeostasis that were greater in more severely injured fish and increased over time. While reflex impairments may predict short term post-release mortality, the prolonged physiological disturbances caused by dermal injuries are likely to be responsible for delayed mortality; our results suggest that disruptions to ion homeostasis is a possible mechanism of post-release mortality.

Capture severity, infectious disease processes and sex influence post-release mortality of sockeye salmon bycatch

Bycatch is a common occurrence in heavily fished areas such as the Fraser River, British Columbia, where fisheries target returning adult Pacific salmon (Oncorhynchus spp.) en route to spawning grounds. The extent to which these encounters reduce fish survival through injury and physiological impairment depends on multiple factors including capture severity, river temperature and infectious agents. In an effort to characterize the mechanisms of post-release mortality and address fishery and managerial concerns regarding specific regulations, wild-caught Early Stuart sockeye salmon (Oncorhynchus nerka) were exposed to either mild (20 s) or severe (20 min) gillnet entanglement and then held at ecologically relevant temperatures throughout their period of river migration (mid-late July) and spawning (early August). Individuals were biopsy sampled immediately after entanglement and at death to measure indicators of stress and immunity, and the infection intensity of 44 potential pathogens. Biopsy alone increased mortality (males: 33%, females: 60%) when compared with non-biopsied controls (males: 7%, females: 15%), indicating high sensitivity to any handling during river migration, especially among females. Mortality did not occur until 5-10 days after entanglement, with severe entanglement resulting in the greatest mortality (males: 62%, females: 90%), followed by mild entanglement (males: 44%, females: 70%). Infection intensities of Flavobacterium psychrophilum and Ceratonova shasta measured at death were greater in fish that died sooner. Physiological indicators of host stress and immunity also differed depending on longevity, and indicated anaerobic metabolism, osmoregulatory failure and altered immune gene regulation in premature mortalities. Together, these results implicate latent effects of entanglement, especially among females, resulting in mortality days or weeks after release. Although any entanglement is potentially detrimental, reducing entanglement durations can improve post-release survival.

Mechanisms to explain purse seine bycatch mortality of coho salmon

Research on fisheries bycatch and discards frequently involves the assessment of reflex impairment, injury, or blood physiology as means of quantifying vitality and predicting post-release mortality, but exceptionally few studies have used all three metrics concurrently. We conducted an experimental purse seine fishery for Pacific salmon in the Juan de Fuca Strait, with a focus on understanding the relationships between different sublethal indicators and whether mortality could be predicted in coho salmon (Oncorhynchus kisutch) bycatch. We monitored mortality using a ~24-h net pen experiment (N = 118) and acoustic telemetry (N = 50), two approaches commonly used to assess bycatch mortality that have rarely been directly compared. Short-term mortality was 21% in the net pen experiment (~24 h) and estimated at 20% for telemetry-tagged fish (~48-96 h). Mortality was predicted by injury and reflex impairment, but only in the net pen experiment. Higher reflex impairment was mirrored by perturbations to plasma ions and lactate, supporting the notion that reflex impairment can be used as a proxy for departure from physiological homeostasis. Reflex impairment also significantly correlated with injury scores, while injury scores were significantly correlated with plasma ion concentrations. The higher time-specific mortality rate in the net pen and the fact that reflexes and injury corresponded with mortality in that experiment, but not in the telemetry-tagged fish released into the wild could be explained partly by confinement stress. While holding experiments offer the potential to provide insights into the underlying causes of mortality, chronic confinement stress can complicate the interpretation of patterns and ultimately affect mortality rates. Collectively, these results help refine our understanding of the different sublethal metrics used to assess bycatch and the mechanisms that can lead to mortality.

Fishing for Effective Conservation: Context and Biotic Variation are Keys to Understanding the Survival of Pacific Salmon after Catch-and-Release

Acute stressors are commonly experienced by wild animals but their effects on fitness rarely are studied in the natural environment. Billions of fish are captured and released annually around the globe across all fishing sectors (e.g., recreational, commercial, subsistence). Whatever the motivation, release often occurs under the assumption of post-release survival. Yet, capture by fisheries (hereafter "fisheries-capture") is likely the most severe acute stressor experienced in the animal's lifetime, which makes the problem of physiological recovery and survival of relevance to biology and conservation. Indeed, fisheries managers require accurate estimates of mortality to better account for total mortality from fishing, while fishers desire guidance on strategies for reducing mortality and maintaining the welfare of released fish, to maximize current and future opportunities for fishing. In partnership with stakeholders, our team has extensively studied the effects of catch-and-release on Pacific salmon in both marine and freshwater environments, using biotelemetry and physiological assessments in a combined laboratory-based and field-based approach. The emergent theme is that post-release rates of mortality are consistently context-specific and can be affected by a suite of interacting biotic and abiotic factors. The fishing gear used, location of a fishery, water temperature, and handling techniques employed by fishers each can dramatically affect survival of the salmon they release. Variation among individuals, co-migrating populations, and between sexes all seem to play a role in the response of fish to capture and in their subsequent survival, potentially driven by pre-capture pathogen-load, maturation states, and inter-individual variation in responsiveness to stress. Although some of these findings are fascinating from a biological perspective, they all create unresolved challenges for managers. We summarize our findings by highlighting the patterns that have emerged most consistently, and point to areas of uncertainty that require further research.

Effects of Modified Handling on the Physiological Stress of Trawled-and-Discarded Yellowfin Bream (Acanthopagrus australis)

Modified handling is often claimed to reduce (sub-)lethal impacts among organisms caught-and-released in fisheries. Improving welfare of discarded fish warrants investigation, when their survival is of both economic and ecological importance. In this study, juvenile yellowfin bream (Acanthopagrus australis) were trawled in an Australian penaeid fishery and then discarded after on-board sorting in either dry or water-filled (modified) trays and with delays in starting sorting of either 2 or 15 mins. Blood plasma cortisol, glucose and potassium were sampled immediately from some yellowfin bream, while others were placed into cages (with controls) and sampled after five days. Irrespective of their on-board handling, all trawled fish incurred a relatively high acute stress response (i.e. an increase in Mean ± SE cortisol from a baseline of <4 to 122.0 ± 14.9 ng/mL) that was mostly attributed to the trawling process, and exacerbated by variation in key parameters (low salinity, changes in water temperature and the presence of jellyfish Catostylus mosaicus in catches). When C. mosaicus was present, the potassium concentrations of fish sampled immediately after sorting were significantly elevated, possibly due to nematocyst contact and subsequent inhibition of ion pumps or cytolysis. Stress also increased during handling in response to warmer air temperatures and longer exposure. While most fish had substantially recovered by 120 hours after discarding, deploying selective trawls (to reduce jellyfish) for short periods and then quickly sorting catches in water would benefit discard welfare.

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

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.

Accounting for escape mortality in fisheries: implications for stock productivity and optimal management

Few studies have considered the management implications of mortality to target fish stocks caused by non-retention in commercial harvest gear (escape mortality). We demonstrate the magnitude of this previously unquantified source of mortality and its implications for the population dynamics of exploited stocks, biological metrics, stock productivity, and optimal management. Non-retention in commercial gillnet fisheries for Pacific salmon (Oncorhynchus spp.) is common and often leads to delayed mortality in spawning populations. This represents losses, not only to fishery harvest, but also in future recruitment to exploited stocks. We estimated incidence of non-retention in Alaskan gillnet fisheries for sockeye salmon (O. nerka) and found disentanglement injuries to be extensive and highly variable between years. Injuries related to non-retention were noted in all spawning populations, and incidence of injury ranged from 6% to 44% of escaped salmon across nine river systems over five years. We also demonstrate that non-retention rates strongly correlate with fishing effort. We applied maximum likelihood and Bayesian approaches to stock-recruitment analyses, discounting estimates of spawning salmon to account for fishery-related mortality in escaped fish. Discounting spawning stock estimates as a function of annual fishing effort improved model fits to historical stock-recruitment data in most modeled systems. This suggests the productivity of exploited stocks has been systematically underestimated. It also suggests that indices of fishing effort may be used to predict escape mortality and correct for losses. Our results illustrate how explicitly accounting for collateral effects of fishery extraction may improve estimates of productivity and better inform management metrics derived from estimates of stock-recruitment analyses.