A Characterization of Bottlenose Dolphin (Tursiops truncatus) Interactions with the Commercial Shrimp Trawl Fishery of South Carolina
Greenman, Justin Theodore
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In the United States, interactions between the shrimp trawl fishery and bottlenose dolphins (<italic>Tursiops truncatus</italic>) are known to exist, however the level of mortality is largely unknown. The current study attempted to determine if interactions between bottlenose dolphins and commercial shrimp trawlers pose a significant threat to dolphin populations and if fishery related mortality is underreported. This was accomplished with a combination of on-board observations, a shrimp fisher mail survey, and stranding record research. On-board observations were made during a 112 day field study consisting of fishery-dependent (Aug. - Dec. 2010) and fishery-independent (Apr. - Nov. 2010 & 2011) sampling. These observations focused on direct physical interactions with the gear and depredation behaviors. Additionally, a sub-sample of shrimp fishers in South Carolina was asked to participate in a mailed survey. The survey included questions related to gear, dolphin observations, and the status of the shrimp fishery. This study also utilized historical dolphin stranding data from the South Carolina Marine Mammal Stranding Network to ascertain signs of shrimp fishery interactions. A three-leveled flow diagram was developed to characterize each stranding case according to the likelihood that mortality resulted from trawler interaction. Field results point to significant dolphin presence around commercial trawlers (chi sq. = 23.406, p <0.001). In addition, survey results showed substantial evidence that fishery related mortality is higher than reported. Finally, stranding records revealed several more cases with signs of possible trawler interaction. Therefore, the current designation of the fishery as a Category II fishery is correct. In addition, increased observer coverage and improved communication with the fishery on the importance of reporting takes is warranted.