Comparison of Two Escapement Designs for Western Painted Turtles Captured in Modified Fyke Nets

Abstract

AbstractAltering sampling methods to reduce bycatch during fish population sampling can introduce biases that affect the capture of target species. Therefore, understanding bycatch reduction devices and how they affect fish sampling is important. Our goal was to test two potential escapement designs intended to reduce bycatch of western painted turtles Chrysemys picta bellii during freshwater-fish population assessments with modified fyke nets. Design A tested an escapement flap on the interior of the modified fyke net and design B tested an escapement throat on the exterior of the modified fyke net. We completed 4-h and 24-h trials for turtle escapement to determine the effectiveness of each design for reducing turtle bycatch. We also simulated fish population assessments to determine the escapement of fish and turtles from each design. Turtles escaped from each design with mean escapement rates during the 4-h and 24-h trials of 71.1% and 63.8% from design A and 55.6% and 50.0% from design B, respectively. In the fish population assessment simulation we observed a mean escapement rate of 49% for turtles from design A, but a mean escapement rate of only 11% from design B. Species-specific escapement rates were observed for fish in both designs. Significant differences in the size structure of some species were observed. Escapement rates from design A were likely underestimated for most species captured due to movement of fish and turtles from the holding pen back into the fyke net. Based on our results, we do not recommend either design to reduce bycatch of turtles during fish community sampling without substantial refinement of the designs. Further research is needed to identify alternative methods for reducing turtle bycatch mortality.