Mitigating bycatch of freshwater turtles in passively fished fyke nets through the use of exclusion and escape modifications

Abstract

Turtles are vulnerable to population declines in response to even low levels of additional adult mortality, for instance bycatch mortality. Inland commercial fisheries that use passive gears such as fyke nets cause the drowning of some freshwater turtles. To reduce fisheries impacts on turtles, bycatch reduction devices (BRDs) successfully implemented in marine systems may be adapted to freshwater systems. We tested the efficacy of two BRDs designed to exclude turtles from fyke nets by comparing catch rates and composition to unmodified nets. We also tested the efficacy of a BRD designed to let turtles escape the net by comparing turtle and fish escape capacities to a large hole in the net. The exclusion device with bars across the net opening significantly reduced turtle catch rates, and both exclusion devices did not affect fish catch rates. With the escape device, all turtles escaped (using painted turtles, Chrysemys picta, as an experimental model) and most (88%) fish were retained while a large hole allowed 60% and 77% of turtles and fish to escape, respectively. The escape device was the most effective for avoiding turtle bycatch mortality while retaining fish. Implementing the escape device or a combination of both exclusion and escape devices would reduce turtle bycatch mortality within fyke net fisheries. However, evaluations are needed to test the effectiveness of escape designs on additional turtle species and in different environments.