Condition and mortality of western painted turtle collected as bycatch in modified fyke nets during fish population assessments

Abstract

Information concerning turtle bycatch and its possible ramifications during biological sampling in freshwater systems is limited. Having such information will enable fisheries researchers and managers to modify fish sampling procedures to potentially minimize any impacts on turtle populations. Therefore, our objective was to utilize reflex response to characterize stress and mortality of western painted turtles (Chrysemys picta bellii) captured as bycatch in modified fyke nets during fish population assessments. Reflex-response-based condition classification (i.e. good, poor, unresponsive) data were collected from May to September during fish population assessments in 38 lakes and seven impoundments in northeast South Dakota from 2012 to 2014. We evaluated the relationship between observed condition and water temperature during two time periods, by turtle gender and size. Turtle bycatch mortality was assessed from June to September during fish population assessments in 14 lakes and three impoundments during 2013 and 2014. Delayed (i.e. overnight) mortality was determined for poor and unresponsive condition classifications and the relationship between observed mortality and water temperature for two time periods, by turtle gender and size was evaluated. Turtle condition decreased as water temperature increased. Condition was poorer during the May and June time period than August and September. Female turtles were in significantly worse condition than males. Condition was not related to turtle size. We observed varying mortality rates across condition classifications and the total estimated delayed mortality rate of known sex turtles was 36.4%. Mortality increased as temperature increased. Delayed mortality rates varied between the two sampling periods with higher mortality rates during the May and June time period. Female turtles had higher mortality rates than males. Delayed mortality did not vary by turtle size. Understanding the negative effects on bycatch during biological sampling is important to provide justification for the development and implementation of measures to protect non-target species.

Turtles and Tortoises Are in Trouble

“…A number of bycatch reduction devices (BRDs) have been designed to reduce this mortality [175,176], but laws regarding their structure and use are unevenly implemented. Research has only recently begun on the effects of fisheries bycatch on freshwater turtle populations [177][178][179][180].…”

“…Hatchling turtles can be reared in captivity until they reach a size that reduces predation risk [185,186]. Existing head-starting programs already release thousands of juveniles into the wild [180,187]. Especially when accompanied by community involvement to allow local people to be stakeholders in the conservation effort, head-starting can be a powerful tool [188].…”

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

“…A promising alternative to reducing bycatch is reducing mortality of bycatch. Recommended methods of reducing bycatch mortality of freshwater turtles include setting nets in shallow water to allow turtles access to air (Bury 2011), sampling at lower water temperature (Moos and Blackwell 2017), and reducing the duration nets are submerged (Bury 2011;Larocque et al 2012a). Potential gear alterations warranting further study include adding an enclosed chimney onto nets and refining the methods employed by Larocque et al (2012c) for floating part of the fyke net to the surface using floats.…”

“…We conducted trials only when surface water temperature was ,208C. Our primary focus was reduced stress on turtles, and at temperatures 208C stress and mortality rates increase for western painted turtles captured in modified fyke nets (Moos and Blackwell 2017). We did not record condition and mortality of turtles in this study.…”

“…Raby et al (2011) noted only 37 of 1,152 papers on bycatch were devoted to freshwater systems. In freshwater environments, high rates of bycatch mortality have been observed in a variety of passive fishing gears (Barko et al 2004), in commercial fisheries (Larocque et al 2012a) and in fisheries management sampling (Moos and Blackwell 2017). However, studies on freshwater turtles have indicated that population declines can occur with only a slight increase in adult mortality (Brooks et al 1991;Congdon et al 1993;Midwood et al 2015).…”