Accidental Bait: Do Deceased Fish Increase Freshwater Turtle Bycatch in Commercial Fyke Nets?

Abstract

Bycatch of turtles in passive inland fyke net fisheries has been poorly studied, yet bycatch is an important conservation issue given the decline in many freshwater turtle populations. Delayed maturity and low natural adult mortality make turtles particularly susceptible to population declines when faced with additional anthropogenic adult mortality such as bycatch. When turtles are captured in fyke nets, the prolonged submergence can lead to stress and subsequent drowning. Fish die within infrequently checked passive fishing nets and dead fish are a potential food source for many freshwater turtles. Dead fish could thus act as attractants and increase turtle captures in fishing nets. We investigated the attraction of turtles to decomposing fish within fyke nets in eastern Ontario. We set fyke nets with either 1 kg of one-day or five-day decomposed fish, or no decomposed fish in the cod-end of the net. Decomposing fish did not alter the capture rate of turtles or fish, nor did it alter the species composition of the catch. Thus, reducing fish mortality in nets using shorter soak times is unlikely to alter turtle bycatch rates since turtles were not attracted by the dead fish. Interestingly, turtle bycatch rates increased as water temperatures did. Water temperature also influences turtle mortality by affecting the duration turtles can remain submerged. We thus suggest that submerged nets to either not be set or have reduced soak times in warm water conditions (e.g., >20 °C) as turtles tend to be captured more frequently and cannot withstand prolonged submergence.

Freshwater turtle bycatch research supports science‐based fisheries management

“…Dead fish in nets may be an attractant for turtles, thus providing another reason for checking nets more frequently and reducing the chances of fish mortality and ensuing turtle catches. Larocque, Watson, Blouin‐Demers, and Cooke (2012) determined whether dead fish were an attractant to turtles by comparing catches in hoop nets with 1‐day deceased fish, 5‐day deceased fish, and no fish. Although there were no differences in turtle or fish catch rates among treatments, water temperature as a covariate in the study indicated that more turtles were captured when the water was warmer.…”