Exercise intensity while hooked is associated with physiological status of longline-captured sharks

The physiological stress response of juvenile nurse sharks (Ginglymostoma cirratum) to catch-and-release recreational angling

Nurse sharks (Ginglymostoma cirratum), especially juveniles, are often encountered by near-shore and shore-based recreational anglers and are suggested to exhibit minimal behavioral and physiological responses to capture, largely based on studies of adults using commercial or scientific fishing methods. To quantify the sub-lethal effects of recreational angling on juvenile nurse sharks, 27 individuals (across 31 angling events) were caught using hook-and-line fishing methods. Over a 30-min period, 4 blood samples were taken with variable time intervals between sampling (i.e., randomized ordering of an interval of 5, 10, and 15 min between each sampling event). Lactate increased by 611% (6.7 ± 2.17 mmol/L) on average over the 30-min fight, and significant relationships were identified between lactate and blood draw number, fight time, and temperature, with large effect sizes. Significant relationships were also detected between blood draw number, glucose, and hematocrit, while osmolality was only affected by fishing site. These results suggest juvenile nurse sharks may exhibit a greater physiological stress response when exposed to recreational angling than adults captured with other fishing methods.

Immunological resilience of a temperate catshark to a simulated marine heatwave

Marine heatwaves (MHWs) have recently been proposed to be more relevant in driving population changes than the continuous increase in average temperatures associated with climate change. The causal processes underpinning MHW effects in sharks are unclear but may be linked to changes in fitness caused by physiological trade-offs that influence the immune response. Considering the scarcity of data about the immune response of sharks under anomalous warming events, the present study analyzed several fitness indices and characterized the immune response (in the blood, epigonal organ, liver, spleen and intestine) of temperate adult small-spotted catsharks (Scyliorhinus canicula) after a 30 day exposure to a category II MHW. The results indicated that adult small-spotted catsharks have developed coping strategies for MHWs. Specifically, among the 35 parameters investigated, only the gonad-to-body ratio (GBR) and plasma glucose concentration showed significant increases. In contrast, gene expression of igm and tumor necrosis factor receptor (tnfr) in blood cells, and tnfr in the epigonal organ, as well as the number of monocytes, all significantly decreased. Although a decline in immune function in small-spotted catsharks was revealed following MHW exposure, energy mobilization restored homeostasis and indicated a shift in energy allocation towards reproduction. Group resilience may be due to the variable tolerance of individuals, the phenotypic plasticity of cellular immunity, thermal imprinting and/or metabolic capacity of the individuals.

A review of elasmobranch catch-and-release science: synthesis of current knowledge, implications for best practice and future research directions

Until relatively recently commercial fisheries have been considered the main driving factor for elasmobranch population declines. However, this belief has begun to shift with the realization that recreational elasmobranch catches may equal or exceed commercial catches in some regions. Many recreational angling fisheries for elasmobranchs involve high participation in catch-and-release angling practices. However, high release rates may not necessarily equate to high survival rates. Therefore, to assist accurate assessment of the potential impact of recreational angling on elasmobranchs, we attempted to summarize and integrate currently available information on specific risk factors associated with recreational angling, alongside associated mortality rates, as well as information on angler behaviour as it relates to identified risk factors. We categorized the major angling-related effects into two groups: injury-induced effects; and biochemical disruption-induced effects; providing a summary of each group and outlining the main lethal and sub-lethal outcomes stemming from these. These outcomes include immediate and delayed post-release mortality, behavioural recovery periods (which may in-turn confer increased predation risks), chronic health impacts and capture-induced parturition and abortion. Additionally, we detailed a range of angling practices and equipment, including hook-type, hook removal and emersion (i.e. air exposure), as well as inter- and intra-specific factors, including aerobic scope, respiratory mode, body size and species-specific behaviours, which are likely to influence injury and/or mortality rates and should therefore be considered when assessing angling-related impacts. We then utilized these data to provide a range of actionable recommendations for both anglers and policymakers which would serve to reduce the population-level impact of recreational angling on these enigmatic animals.

Individual residency behaviours and seasonal long-distance movements in acoustically tagged Caribbean reef sharks in the Cayman Islands

Understanding how reef-associated sharks use coastal waters through their ontogeny is important for their effective conservation and management. This study used the horizontal movements of acoustically tagged Caribbean reef sharks (Carcharhinus perezi) to examine their use of coastal space around the Cayman Islands between 2009 and 2019. A total of 39 (59.1%) tagged sharks (male = 22, female = 17, immature = 18, mature = 21) were detected on the islands wide network of acoustic receivers. The detection data were used to calculate values of Residency Index (RI), Site-Fidelity Index (SFI) and minimum linear displacement (MLD), as well as for network analysis of individual shark movements to test for differences between demographics, seasons, and diel periods. Sharks were detected for up to 1,598 days post-tagging and some individuals showed resident behaviour but the majority of tagged individuals appear to have been one-off or only occasional transient visitors to the area. Generally, individuals showed strong site-fidelity to different areas displaying linear home ranges of < 20 km. The evidence indicates that there was no pattern of diel behaviour. Tagged sharks generally showed increased movements within and between islands during the summer (April-September), which may be related to breeding activity. Some individuals even made occasional excursions across 110 km of open water > 2,000 m deep between Grand Cayman and Little Cayman. One mature female shark showed a displacement of 148.21 km, the greatest distance reported for this species. The data shows that the distances over which some sharks moved, greatly exceeded the extent of any one of the islands' marine protected areas indicating that this species may be more mobile and dispersive than previously thought. This study provides support for the blanket protection to all sharks throughout Cayman waters, which was incorporated within the National Conservation Act in 2015.

First report on the serum chemistry and haematology of free-ranging dusky (Carcharhinus obscurus) and sandbar (Carcharhinus plumbeus) sharks in the eastern Mediterranean Sea

Shark assessments in the Mediterranean Sea are still scarce, and serum chemistry and haematological data have yet to be reported for wild dusky (Carcharhinus obscurus) or sandbar (Carcharhinus plumbeus) shark populations in the Mediterranean Sea. Herein, blood samples were obtained from adult dusky (n = 23) and sandbar (n = 14) sharks from an aggregation site near the Hadera power and desalination plants in Israel in the winters of 2016-20. Several serum chemistry analytes were characterized with relation to stress, body size and environmental conditions. Glucose concentrations were higher, while total cholesterol concentrations were lower in dusky sharks than in sandbar sharks, potentially due to distinct metabolic pathways utilized during the capture-related activity by both species. However, differences in sex and size are noted and should be considered. The blood cell morphology of both species was consistent with previous findings for sandbar sharks. Atypical monocytes were noted in one dusky shark. Preliminary and exploratory reference intervals for female dusky sharks were calculated for glucose, triglycerides, total cholesterol, total protein and creatine kinase. These data must be viewed with caution due to the potential influence of capture-related stress on analyte concentrations and activities and the fact that only females were employed in the calculations. Moreover, the sampling site is adjacent to coastal power and desalination plants, which may significantly affect shark physiology. Although limited, this novel database on dusky and sandbar shark serum chemistry and haematology aspects is essential as a first attempt to obtain data on these species in the eastern Mediterranean Sea and for future conservation and long-term biomonitoring efforts.

Elasmobranchs as bioindicators of pollution in the marine environment

Bioindicator species are increasingly valuable in environmental pollution monitoring, and elasmobranch species include many suitable candidates for that role. By measuring contaminants and employing biomarkers of effect in relevant elasmobranch species, scientists may gain important insights about the impacts of pollution in marine ecosystems. This review compiles biomarkers applied in elasmobranchs to assess the effect of pollutants (e.g., metals, persistent organic pollutants, and plastics), and the environmental changes induced by anthropogenic activities (e.g., shifts in marine temperature, pH, and oxygenation). Over 30 biomarkers measured in more than 12 species were examined, including biotransformation biomarkers (e.g., cytochrome P450 1A), oxidative stress-related biomarkers (e.g., superoxide anion, lipid peroxidation, catalase, and vitamins), stress proteins (e.g., heat shock protein 70), reproductive and endocrine biomarkers (e.g., vitellogenin), osmoregulation biomarkers (e.g., trimethylamine N-oxide, Na⁺/K⁺-ATPase, and plasma ions), energetic and neurotoxic biomarkers (e.g., lactate dehydrogenase, lactate, and cholinesterases), and histopathological and morphologic biomarkers (e.g., tissue lesions and gross indices).

Connecting post-release mortality to the physiological stress response of large coastal sharks in a commercial longline fishery

Bycatch mortality is a major factor contributing to shark population declines. Post-release mortality (PRM) is particularly difficult to quantify, limiting the accuracy of stock assessments. We paired blood-stress physiology with animal-borne accelerometers to quantify PRM rates of sharks caught in a commercial bottom longline fishery. Blood was sampled from the same individuals that were tagged, providing direct correlation between stress physiology and animal fate for sandbar (Carcharhinus plumbeus, N = 130), blacktip (C. limbatus, N = 105), tiger (Galeocerdo cuvier, N = 52), spinner (C. brevipinna, N = 14), and bull sharks (C. leucas, N = 14). PRM rates ranged from 2% and 3% PRM in tiger and sandbar sharks to 42% and 71% PRM in blacktip and spinner sharks, respectively. Decision trees based on blood values predicted mortality with >67% accuracy in blacktip and spinner sharks, and >99% accuracy in sandbar sharks. Ninety percent of PRM occurred within 5 h after release and 59% within 2 h. Blood physiology indicated that PRM was primarily associated with acidosis and increases in plasma potassium levels. Total fishing mortality reached 62% for blacktip and 89% for spinner sharks, which may be under-estimates given that some soak times were shortened to focus on PRM. Our findings suggest that no-take regulations may be beneficial for sandbar, tiger, and bull sharks, but less effective for more susceptible species such as blacktip and spinner sharks.

Simulated heatwave and fishing stressors alter corticosteroid and energy balance in neonate blacktip reef sharks, Carcharhinus melanopterus

The increasing frequency and duration of marine heatwaves attributed to climate change threatens coastal elasmobranchs and may exacerbate existing anthropogenic stressors. While the elasmobranch stress response has been well studied, the role of the unique corticosteroid-1α-hydroxycorticosterone (1α-OHB)-in energy balance is not understood. Therefore, 1α-OHB's utility as a stress biomarker in elasmobranch conservation physiology is equivocal. Here, we analyse the roles of corticosteroids, 1α-OHB and corticosterone, and metabolites, glucose and 3-hydroxybutyrate (3-HB), in response to stress in a protected tropical shark species, the blacktip reef shark (Carcharhinus melanopterus). Wild-caught neonates were exposed to ambient (27°C) or heatwave conditions (29°C) and subsequently a simulated fishing stressor (1 min air exposure). Blood samples were taken prior to temperature exposure, prior to air exposure, and 30 min, 1 h, 24 h, and 48 h post-air exposure at treatment temperatures. Plasma 1α-OHB was elevated for 48 h in 27°C-exposed sharks but declined over time in 29°C-exposed sharks. Plasma 1α-OHB was not correlated with either metabolite. Plasma glucose was higher and plasma 3-HB was lower in 29°C-exposed sharks. In a separate experiment, blood samples were collected from both neonate and adult sharks immediately following capture and again 5 min later, and analysed for corticosteroids and metabolites. Plasma 1α-OHB increased in neonates within 5 min, but neonates displayed lower plasma 1α-OHB and higher glucose concentrations than adults. We conclude that 1α-OHB does not serve as a classic glucocorticoid role in C. melanopterus under these stressors. Furthermore, we show for the first time, ontogenetic differences in plasma 1α-OHB. Ultimately, our findings provide insights into hormonal control of energy mobilization during stress in C. melanopterus, particularly during simulated heatwave conditions, which seem to alter both endocrine and energy mobilization. Further work is needed to determine the utility of 1α-OHB as a biomarker for the mobilization of energy during a stress event in elasmobranchs.

Physiological response to capture stress in endemic Southern African catsharks (family Scyliorhinidae)

Fishing is the major threat to marine fish populations, particularly to higher trophic-level predators such as sharks. Many sharks, and other fish, are caught as commercial by-catch or for recreational purposes and then released; therefore, it is important to understand the effects of capture stress on their physiology and subsequent survival. Nonetheless, although important data have been collected for some sharks, there can be substantial interspecific differences, and the consequences of capture stress are still poorly understood for most species. In this study, the authors quantified the physiological effect of capture on four catshark species endemic to Southern Africa, which are regularly discarded as by-catch and targeted by recreational fisheries. Fifteen pyjama sharks, nine leopard sharks and nine shysharks were captured, and a blood sample was collected to measure their physiological response to capture stress. Stressed blood biochemistry was compared to samples obtained after the sharks recovered for 24 h in an underwater pen. Levels of pH and K⁺ were significantly lower, and lactate levels were significantly higher, in sharks immediately after capture stress compared to after the 24 h recovery period. Although the species showed a similar response to capture stress, they differed significantly in pH, K⁺ and lactate levels, and there was some evidence of size affecting the strength of the response to capture stress. The substantial physiological response elicited by even the relatively quick capture event in this study suggests that common fishing practices will have a stronger impact on catshark homeostasis because of longer hooking times and more disruptive fishing gear. Although the relationship between survival and physiological changes elicited by capture needs further investigation, the results provide further evidence that minimizing stress would be beneficial to maximize the survival of sharks and other fish following capture-and-release fishing practices.

Lack of impact of radiation on blood physiology biomarkers of Chernobyl tree frogs

BACKGROUND

Human actions have altered natural ecosystems worldwide. Among the many pollutants released to the environment, ionizing radiation can cause severe damage at different molecular and functional levels. The accident in the Chernobyl Nuclear Power Plant (1986) caused the largest release of ionizing radiation to the environment in human history. Here, we examined the impact of the current exposure to ionizing radiation on blood physiology biomarkers of adult males of the Eastern tree frog (Hyla orientalis) inhabiting within and outside the Chernobyl Exclusion Zone. We measured the levels of eight blood parameters (sodium, potassium, chloride, ionized calcium, total carbon dioxide, glucose, urea nitrogen, and anion gap), physiological markers of homeostasis, as well as of liver and kidney function.

RESULTS

Levels of blood physiology biomarkers did not vary in function of the current exposure of tree frogs to ionizing radiation within the Chernobyl Exclusion Zone. Physiological blood levels were similar in frogs inhabiting Chernobyl (both in areas with medium-high or low radiation) than in tree frogs living outside Chernobyl exposed only to background radiation levels.

CONCLUSIONS

The observed lack of effects of current radiation levels on blood biomarkers can be a consequence of the low levels of radiation currently experienced by Chernobyl tree frogs, but also to the fact that our sampling was restricted to active breeding males, i.e. potentially healthy adult individuals. Despite the clear absence of effects of current radiation levels on physiological blood parameters in tree frogs, more research covering different life stages and ecological scenarios is still needed to clarify the impact of ionizing radiation on the physiology, ecology, and dynamics of wildlife inhabiting radioactive-contaminated areas.

Variation of body condition and plasma energy substrates with life stage, sex, and season in wild-sampled nurse sharks Ginglymostoma cirratum

Reported here are the relationships among morphological (i.e., body condition) and biochemical (i.e., plasma concentrations of triglycerides, cholesterol, free fatty acids, and ketone bodies and ketone body ratios) parameters related to energy storage and use, as well as the variation of such parameters, for 107 free-ranging nurse sharks Ginglymostoma cirratum sampled off South Florida. Immature G. cirratum exhibited a higher variance in body condition, plasma free fatty acid concentrations and ketone body ratios compared to adults. Mature female G. cirratum had significantly higher body condition than mature males, driven by a seasonal increase in mature female body condition during the wet season. Mature male G. cirratum showed a decrease in the ketone body β-hydroxybutyric acid during the dry season. Taken together, this study provides a baseline assessment of body condition and internal physiological state for a data-poor marine species and demonstrates significant ontogenetic, sexual and seasonal variation in G. cirratum energetic state. As concluded by other studies of energy metabolism in free-ranging sharks, this research highlights the importance of considering intraspecific patterns and sampling context for inferring the drivers of variation.

Blood biochemical status of deep-sea sharks following longline capture in the Gulf of Mexico

Prior to the Deepwater Horizon (DWH) oil spill, little research effort was focused on studying deep-sea sharks in the Gulf of Mexico (GoM). While the biology of these fishes remains virtually unknown, they are routinely captured in commercial fisheries as bycatch. In the absence of basic biological data, and with the probability of post-release survival unknown for most species, effective management plans cannot be formulated, making populations highly susceptible to overfishing. Any potential detrimental effects of the DWH oil spill, which occurred at 1500 m deep, are also unknown. Following longline capture, we characterized the physiological blood biochemical parameters related to secondary stress and compared them among seven shark species occurring on the continental shelf edge and slope in the GoM at depths ranging from 200 to 2000 m. We also investigated the relationship between blood parameters and depth as well as proximity to the oil spill site. The deep-sea sharks examined here exhibited variability in blood chemistry associated with the secondary stress response, with values falling within published records for previously studied elasmobranchs. Results suggested that there is greater relative physiological stress in shallower-dwelling sharks as well as smaller-bodied sharks. Further, the rate of core temperature warming was fastest in smaller bodied sharks, which likely contributes to greater physiological stress. The core temperatures of the larger-bodied, deeper-dwelling species were not altered as drastically as the smaller-bodied sharks after being hauled to the surface. Any chronic physiological effects of the oil spill were not detectable as there were no relevant correlations between blood chemistry metrics and proximity to the DWH oil spill site.