CURRENT KNOWLEDGE
The assumption in catch and release angling is that a large proportion of released animals recover and survive. However, the fate of angled fish post-release has been shown to vary according to the environment, angling method and species. Due to inter-species differences in capture resilience, “good practice” catch and release guidelines should be species-specific, requiring research on the wide range of shark species across representative habitats in order to successfully implement catch and release fishing as a conservation measure.
Existing Literature
We conducted a comprehensive review of the existing literature on shark survivorship, which allowed us to highlight areas in need of further research. The specific aims of this review were:
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Outline the science behind shark catch and release guidelines,
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Refine global elasmobranch catch and release guidelines to improve implementation,
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Identify areas where future research is needed,
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Suggest refinements to the methods in use for the study of elasmobranch (sharks, skates and rays) catch and release.
Results
As of 2020, only eight peer-reviewed studies on the effects of catch-and-release fishing of sharks have been published. These studies were conducted in the North Atlantic, Gulf of Mexico, North Pacific, and South Pacific, and included the following species: Atlantic sharpnose shark (Rhizoprionodon terraenovae), blacktip shark (Carcharhinus limbatus), common thresher shark (Alopias vulpinus), lemon shark (Negaprion brevirostris), sand tiger shark (Carcharias taurus), and shortfin mako (Isurus oxyrinchus). Only two of those (thresher sharks and shortfin makos) can sometimes be seen in UK waters. The studies all focused on the relative impact that different stages of the angling process had on post-release survival, though not all stages were examined in every study. Of the angling steps, fight time was the most investigated (86% of studies), followed by hooking (75% of studies), boarding and handling (each 25% of studies), and unhooking (13%). No study explicitly considered the potential positive effects of revival, and they did not include any analysis of the recovery behaviour (i.e. How does the shark behave post-release? How long does the shark take to resume "normal" behaviour? How does this affect its chances of survival?).
Factors influencing post-release survivorship
Although general trends need to be extrapolated carefully when few studies are available, hook type and hooking location were the factors that showed the clearest trends in their effect on post-release survival (PRS in the figure below). Hooking location was related to post-release survivorship in 67% of studies that investigated hooking location as a factor (n=6), with deep or foul hooking (i.e. the hook was set deep into the mouth or even the gut, or on the fins and tail) often causing a clear decline in the chances of post-release survival. Species-specific differences were evident in the effect of circle versus “J” hooks, with circle hooks reducing deep hooking in shortfin mako but not blacktip sharks.
No study has so far demonstrated a clear effect of boarding or unhooking on post-release survivorship. However, longer handling times were also found to cause increased concentrations of blood lactate (the metabolic compound often associated to stress) and other changes in blood chemistry that indicate ongoing stress. Two studies on blacktip sharks investigated handling as a factor in survivorship, with one identifying a positive relationship (careful handling somewhat increased the chances of survival) and the other no relationship. This suggests that different species likely react differently to handling.
Summary of recreational fishing effects on post-release survivorship of shark species. Horizontal flow diagrams (filled arrows) representing the recreational fishing process and relevant environmental and physiological factors influencing post-release survivorship (PRS). Filled arrows represent the effects of angling stages on post-release survivorship (relationship and directionality). A "positive" (green) relationship means an increase in PRS, a "negative" relationship means a decrease in PRS. Greyed out arrows denote steps that were not tested in the study. Connecting black arrows and braces denote inter-process relationships and arrows by the side of boxes indicate the direction of the effect. Sea Surface Temperature (SST).
Future Research
The summarised indicates that several well-studied angling steps can be efficacious in improving post-release survivorship in sharks (proper hook type and hooking location, careful and quick handling). However, there are several elements that remain understudied and that, we believe, could further increase survivorship in catch and release shark fisheries if better understood:
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The preparedness and skill of anglers is likely to have an effect on the capture experience of pelagic sharks, but is challenging to quantify and often overlooked in experimental design. Studies looking to comprehensively describe the full capture experience should take this into account.
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Clearly, there are some species that are more susceptible to angling stress than others. These species would require specific actions when being targeted. A comprehensive review of species-specific effects in both recreational and commercial fisheries could indicate which these species are.
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Leader type has been identified in commercial fisheries as having an effect on post-release survivorship for certain sensitive species. However, this relationship has not been investigated in a recreational setting. Wire leaders, which were identified by Gilman et al. (2016) to decrease survivorship, are a common choice in shark fisheries and a change to another leader type (e.g. monofilament) could prove successful in reducing mortality.
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Revival is often not considered in catch and release science and could represent a key area for improvement. For example, the increasing availability and application of accelerometers and gyroscope-enabled tags for catch and release could inform specific revival techniques based on the behavioural recovery tactics of released individuals.
Literature
Over the duration of the project we will update this page with new research, updated guidelines and other resources as they become available. Details of existing research referenced on this website, including links to source material, can be found below.
Gurshin, C. W. D., and S. T. Szedlmayer. "Short‐term survival and movements of Atlantic sharpnose sharks captured by hook‐and‐line in the north‐east Gulf of Mexico." Journal of Fish Biology 65.4 (2004): 973-986. Link
Heberer, C., et al. "Insights into catch-and-release survivorship and stress-induced blood biochemistry of common thresher sharks (Alopias vulpinus) captured in the southern California recreational fishery." Fisheries Research 106.3 (2010): 495-500. Link
Kneebone, Jeff, et al. "The physiological effects of capture stress, recovery, and post-release survivorship of juvenile sand tigers (Carcharias taurus) caught on rod and reel." Fisheries Research 147 (2013): 103-114. Link
Danylchuk, Andy J., et al. "Hooking injury, physiological status and short-term mortality of juvenile lemon sharks (Negaprion bevirostris) following catch-and-release recreational angling." Conservation Physiology 2.1 (2014): cot036. Link
Sepulveda, C. A., et al. "Post-release survivorship studies on common thresher sharks (Alopias vulpinus) captured in the southern California recreational fishery." Fisheries Research 161 (2015): 102-108. Link
French, Robert P., et al. "High survivorship after catch-and-release fishing suggests physiological resilience in the endothermic shortfin mako shark (Isurus oxyrinchus)." Conservation Physiology 3.1 (2015). Link
Whitney, Nicholas M., et al. "The physiological stress response, postrelease behavior, and mortality of blacktip sharks (Carcharhinus limbatus) caught on circle and J-hooks in the Florida recreational fishery." Fishery Bulletin 115.4 (2017):532-544. Link
Mohan, J.A., Jones, E.R., Hendon, J.M., Falterman, B., Boswell, K.M., Hoffmayer, E.R. and Wells, R.D., 2020. Capture stress and post-release mortality of blacktip sharks in recreational charter fisheries of the Gulf of Mexico. Conservation Physiology, 8(1), p.coaa041. Link