Abstract:
Conflicts between marine mammals and fisheries can be attributed to spatial overlap and
resource competition between cetaceans and fisheries and/or behavioral learning among
marine mammals. In the present study, I documented depredation by bottlenose dolphins
(Tursiops truncatus) in Florida’s king mackerel troll fishery. Depredation refers to the
behavior in which predator species remove or damage fish on fishing lines or in nets. I
conducted twenty-six surveys of charter and commercial fishermen in Islamorada,
Florida and twenty-three along Florida’s east coast from Fort Pierce south to Lake Worth
Inlet, and I observed dolphin behaviors from working vessels in these two study sites.
All survey respondents indicated they had observed bottlenose dolphins depredating bait
or catch. Fishermen reported that king mackerel was the species most often taken by
bottlenose dolphins. From behavioral observations, I found that dolphins took 6% of
king mackerel caught by charter fishermen and 20% of fish caught by commercial
fishermen. I attributed these differences to seasonal variation in fish distribution or gear
differences between vessel types. Preliminary tests demonstrated that a modification to
the outrigger planar will successfully deter bottlenose dolphins from engaging in
depredation, without causing a reduction in catch.
