Term of Award
Master of Science in Biology (M.S.)
Document Type and Release Option
Thesis (open access)
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This work is licensed under a Creative Commons Attribution 4.0 License.
Department of Biology
Committee Member 1
Committee Member 2
The Georgia shrimp fishery has seen a dramatic decrease in profit and productivity since the 1980’s due to a number of economic factors. Additional, yet undocumented, pressures on this fishery include interactions between foraging sharks with trawl gear. Fishermen report that sharks frequently bite nets in an attempt to prey on netted fish, resulting in large holes in the gear. Further elasmobranch interactions with trawl gear occur as bycatch; shrimp trawls represent nearly 100% of elasmobranch commercial bycatch in Georgia state waters, the species composition of which is largely unstudied. Shark interactions with nets were detailed through fishery-dependent observations on commercial shrimp boats in Georgia (n= 6 vessels). Number of damaged sites, location of damage on the net, estimated repair time, and many fishing/environmental variables were recorded for 96 trawling events May 2016 - November 2017. Sharks bit on average 1.51 holes (± 0.2 SE) in the nets for every trawl. Shark depredation was correlated negatively with vessel speed (r=-0.2814, p=0.005), and positively with the duration and number of nets (r=0.2799, p=0.006). As a result, fishermen spent of average estimated time of 27 minutes repairing equipment for every trawl they make in a day of fishing. Fishermen were also asked questions related to their perceptions towards this issue for qualitative analysis. Elasmobranch bycatch was also identified and measured for each trawl. Of fifteen total species caught, three species in particular accounted for 76.7% of all elasmobranch bycatch (n=84 trawls, 2247 individuals): Rhizoprionodon terraenovae (CPUE = 4.2 individuals/hm2 area trawled ± 0.83 SE), Hypanus sabinus (CPUE =1.736 ± 0.29), and Gymnura micrura (CPUE =1.6 ± 0.22). Because the fishery has decreased in size and effort over the last two decades, further analysis and monitoring is needed to determine if bycatch in shrimp trawls are drastically decreasing stock sizes in elasmobranch species.
Scanlon, Matthew M., "Evaluating Elasmobranch Bycatch and Shark Depredation in the Georgia Shrimp Fishery" (2018). Electronic Theses and Dissertations. 1801.
Research Data and Supplementary Material