Abstract
The impacts of fisheries capture on the physiology, behavior, and survival of sharks have previously been investigated via both laboratory and field studies, and have primarily been conducted in temperate waters on species commonly encountered in pelagic commercial fisheries, or with juveniles of small species which can be easily maintained in captivity. In contrast, relatively little attention has been directed towards shark capture stress and survival research in subtropical or coastal areas which contain a higher diversity of species that can also be fished nearly year-round by both commercial and recreational industries. Furthermore, the vast majority of previous work to date has relied heavily on comparing means between species for selected parameters without investigating the gradients in fishery-related variables such as hooking duration, water temperature, and animal size on stress and survival rates. Most studies have focused on either physiology or survival rates (either at-vessel, or post-release), and have not integrated methods to study the combined effects of capture for an improved assessment of vulnerability. Moreover, previous work has not included evaluations of shark behavior when captured, nor the human dimensions component (i.e., angler perceptions of risk) of capture and release. To address these knowledge gaps, I conducted an integrated, multipronged dissertation to assess shark vulnerability to fisheries interactions. To evaluate which factors affected shark survival, I first examined a database on shark survival in the National Marine Fisheries Service’s Pelagic Observer Program and investigated the at-vessel survival of 12 shark species captured as bycatch over 12 years in the US Atlantic pelagic longline fishery. I used regression to model survival inclusive of recorded fishery-related variables which would potentially affect catch/survival for each species. After identifying a range of species-specific survival rates, I then used an experimental approach to investigate the physiological reactions, behavioral responses and survival outcomes of six coastal shark species to fisheries interactions (the process of capture and release). I performed a series of integrated field studies, including (1) blood physiological sampling, reflex performance analysis, and biotelemetry; and (2) high-resolution analysis of behavioral responses using accelerometers attached to fishing gear. Finally, I surveyed Florida saltwater recreational anglers on their conservation attitudes and perceptions towards sharks and their vulnerability to post-release mortality resulting from capture and release. Using these data, I tested the following major hypotheses: (1-null) there would be no species-specific influences of operational, environmental, or biological variables on the at-vessel hooking survival of sharks captured as bycatch; (2) the magnitude of physiological disturbance and reflex impairment in captured sharks would be correlated with hooking duration; (3) physiological disturbance and reflex impairment would be significantly influenced by biological characteristics including shark size and species; (4) satellite telemetry reporting rates would be lowest for species exhibiting higher physiological disturbance and reflex impairment; (5) species with the lowest survival rates and highest physiological stress responses would show the greatest acceleration and fighting intensities; (6) fisher demographic and subjective knowledge variables would have no influence on their conservation ethic or perceptions of shark vulnerability to recreational fishing activities; (7) anglers would not rank the threatened status of shark species differently. Results from the longline assessment indicated that survival for seven of the 12 pelagic shark species was significantly affected by at least one operational, environmental, or biological variable, and that survival rates ranged from low (33%, night shark) to very high (97%, tiger shark). Species with the highest vulnerability rankings exhibited low survival rates, low reproductive potential, and slow attainment of maturity. Field results suggested that the physiological parameter most indicative of exhaustive exercise (i.e., lactate) was significantly correlated with hooking duration and animal size. Survival rates from empirical satellite tagging efforts significantly differed between species, ranging from ~50% in great hammerhead sharks to almost 100% in tiger sharks. Sharks with the highest stress responses (blood physiology and reflex impairment) and lowest survival rates exhibited the highest acceleration forces and rates when hooked, and these species tended to exhibit lifestyles with higher metabolic demands. Survey results suggested that fishers generally comprehended the issues of post-release mortality and sharks as a species of conservation concern, but the concept of inherent species vulnerability in capture and release interactions was less understood. For the most part, the sample of anglers also ranked the vulnerabilities of shark species similarly to those obtained empirically in other parts of this dissertation. By combining results from my field studies in Florida, a range of vulnerabilities to fisheries capture and release were evident for the six species, and were distributed as follows (from most vulnerable to least vulnerable): Great hammerhead, blacktip, bull, lemon, tiger, nurse. Overall, the findings from this dissertation suggest that: (1) Shark vulnerability and the manner in which biotic and abiotic factors affect stress and survival in fisheries interactions is highly species-specific; (2) Species exhibiting the most pronounced physiological and behavioral stress responses, lowest survival rates at-vessel and post-release, and highest vulnerability appear to be species with high metabolic rates, active lifestyles, and specialized morphology or ecology; (3) life-history correlates of biological productivity in isolation do not explain species’ vulnerability; (4) a perceived knowledge of shark conservation issues in the angling community may be one of the best predictors of conservation-based choices and behaviors; namely the willingness to select species as ‘threatened’ and adopt additional management tools for species’ recovery; (5) a combination of species-specific guidelines (capture regulations, avoiding or limiting encounters) and ecosystem-based management tools (marine protected areas) may provide the greatest benefits for species which are highly vulnerable to fisheries interactions and currently in decline, such as hammerhead sharks; and (6) evolutionary and ecological variables or traits may be useful in understanding patterns of shark vulnerability to human-induced stressors .