Research Project: Post-release mortality and behavior of sharks in shore-based recreational fisheries using citizen scientists and low-cost tags
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Recreational shark fishing has become increasingly popular in recent decades, especially shore-based fishing that has provided access to a broad demographic of anglers. Catch and release shark fishing has become best practice to limit deleterious effects on overall stocks, but species-specific stress levels and post-release mortality in shore-based fisheries is unclear. Advances in electronic tagging technology, including acceleration data loggers (ADLs) and pop-up satellite archival transmitting (PSAT) tags, now provide unprecedented insight into fine scale (e.g. seconds to minutes with ADLs) and long term (e.g. daily to monthly with PSAT) behavior of sharks post-release. Using electronic tags, research has demonstrated that the physical injury and physiological stress inflicted upon sharks caught and released contributes directly to post-release mortality (PRM), which can occur immediately or as a result of cumulative sub-lethal effects causing fitness losses over time. Currently, PRM estimates from boat-based shark fisheries are primarily used to inform management strategies and research into the contribution of shore-based shark fishing to overall PRM rates is lacking. This project cooperatively engaged recreational shore-based shark anglers to deploy ADLs and PSATs on blacktip, bull, tiger and hammerhead sharks (Sphyrna spp.) to estimate post-release behavior and mortality rates. These species vary in physiological sensitivity to capture from highly sensitive (hammerhead species) to less sensitive (tiger) and the tagging approach ensured increased tag deployment rates in unpredictable but diverse catches to explore species specific mortality rates. The objectives of the study were: 1) Characterize both fine and broad-scale post-release behavior and mortality of beach-caught sharks in Texas using ADLs and PSATs deployed by experienced recreational fishermen; 2) Compare behavioral capture responses among diverse shark species with variable capture-sensitivities (blacktip, bull, tiger, hammerhead species) and seasonal environmental variables; 3) Host both pre- and post-tagging shark angler workshops to train anglers in shark identification, disseminate tagging results and discuss how results can be applied to shark conservation efforts. Sharks were captured by recreational shore-based anglers from August 2018 to October 2021. For each captured shark, fight time, handling time, and biological metrics including length and sex were recorded, and release condition was scored as good, fair, poor, or dead.
Of the 21 PSATs deployed, 8 PSAT tags were recovered and provided high-resolution archived data for temperature, light level, and depth measurements every few seconds to confidently determine shark outcomes. Six sharks survived and 2 sharks experienced mortality 10 minutes to 1.25 hours after release. Seven tags transmitted limited data, but the data was sufficient to determine shark status based on high-resolution depth data for the final 5 days of deployment and daily summaries for minimum and maximum depths, temperature, and light levels: 7 sharks survived, and 1 shark experienced mortality immediately after release. 1 tag on a shark that experienced mortality less than 10 min after release returned light level, depth, and temperature data that was sufficient to determine the shark was ingested by a predator. Six tags did not transmit any data after deployment and thus we cannot determine the post-release fate of those sharks. The PRM rate across all the PSAT tags was therefore found to be 20% (3/15) (Table 1; Appendix 1).
Of the 22 ADLs deployed, 4 were not recovered or programming/battery/user error provided no data. 18 ADLs were recovered for analysis: 13 sharks survived, and 5 sharks experienced mortality within seconds up to 5 hours post release. The PRM rate across all the ADL tags was therefore found to be 27.8% (5/18) (Table 2; Appendix 2). Across both tag types a total of 20 bull sharks were caught and tagged: 1 shark experienced mortality, 13 sharks survived, and 6 tags had unknown fates due to tag malfunction. The post-release mortality rate for bull sharks was therefore estimated to be 7.1% (1/14). A total of 14 blacktip sharks were caught and tagged: 5 sharks experienced mortality, 5 sharks survived, and 4 tags did not transmit any data. The post-release mortality rate for blacktip sharks was therefore estimated to be 50% (5/10). A total of 5 tiger sharks were caught and tagged and all survived, suggesting 0% mortality. However, one tiger shark exhibited mortality 41 days after tagging that was categorized as a natural mortality and not due to capture stress. That said, the cumulative sub-lethal effects of tagging such as gear left in the body or infection at the tagging site could have significantly reduced fitness, resulting in a delayed post-release mortality. Although scalloped hammerheads were originally targeted, 2 great hammerheads were caught and tagged: 1 experienced immediate mortality and was ingested, and 1 survived up to 16 days following release. The mortality rate for great hammerheads was therefore estimated at 50%.
Understanding how fishing mortality rates may differ between shore-based and boat-based recreational fleets and across different species is essential for accurately assigning gear type and mortality estimates in stock assessment models. Angler outreach and education was achieved by PIs attending the Sharkathon shore-based fishing tournament in October 2021, reaching hundreds of participating anglers, even though 2020 survey ambitions were delayed due to COVID19. Follow-up angler surveys will occur in 2022 after finalizing/publishing results to generate reference data on angler attitude and response to research results. In summary, this collaborative project combined cooperative angler citizen scientists and advanced electronic tags to provide an empirically derived post-release mortality rate estimate across different species in a recreational shore-based fishery for use in management protocols.
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