Seasonal patterns in bycatch composition and mortality associated with a freshwater hoop net fishery

Abstract

Although bycatch is well known and well studied in marine fisheries, comparatively little is known about bycatch in freshwater fisheries. Even basic information on bycatch composition and mortality in freshwater is unavailable, given that few inland jurisdictions require reporting of bycatch. A small-scale inland hoop net fishery that targets pan fish (e.g. sunfish, Lepomis spp.) and operates primarily in the spring and fall was simulated in two lakes in south-eastern Ontario to characterize both bycatch composition and mortality. We fished one lake in both spring and fall to compare catch rates, while in the other lake we set nets for 2 or 6 days during the spring to assess fish mortality associated with different net tending frequencies. In both lakes, bycatch consisted of gamefish, turtles (including several species at risk), and mammals. For fish, there was no difference in spring and fall catches. Turtles, however, were captured more often in spring. Fish mortality of both target and non-target species increased from 0.3-0.9% to 3.0-3.7% (4-10 times) when set net duration increased from 2 to 6 days. Despite the provision of an air breathing space in our nets, we documented severe turtle mortality (33% in one lake) and all mammals died, suggesting that provision of air spaces is not always effective. Although all bycatch mortality is a concern, turtles are prone to population declines even with low levels of non-natural mortality. As such, regulators may consider limiting commercial fishing to the fall in this region to reduce turtle captures. Seasonal restrictions on fishing or use of frequent net tending (e.g. < 2 days) will not prevent all turtle bycatch and therefore gear modifications should be investigated to further reduce turtle captures and mortality associated with hoop nets. Animal Conservation. Print ISSN 1367-9430 Animal Conservation 15 (2012) 53-60

Physiological disturbances and behavioural impairment associated with the incidental capture of freshwater turtles in a commercial fyke-net fishery

“…Nets were fished in pairs and were attached by leads (see Fig. 1 in Larocque et al 2012a). Each net contained 7 steel hoops, which were 0.5 m apart and 0.9 m in diameter, with 2 throats located in the second and fourth hoop.…”

“…We used fyke nets similar to those used in the local commercial fishery to collect turtles following the methods outlined by Larocque et al (2012a). Nets were fished in pairs and were attached by leads (see Fig.…”

“…Commercial fishing in that region occurs on inland lakes and rivers, with sunfish Lepomis spp. being the primary targeted species, in addition to bullhead Ameiurus spp., yellow perch Perca flavescens, black crappie Pomoxis nigromaculatus and rock bass Ambloplites rupestris (Burns 2007, Larocque et al 2012a. The habitats of freshwater turtles and targeted commercial fish overlap, thus increasing the possibility of turtle entrapment (Carrière et al 2009, Larocque et al 2012a.…”

“…A variety of marine turtle bycatch reduction strategies have been developed and tested (UN FAO 2009), including the turtle excluder device, which has prevented the accidental capture of turtles in the shrimp trawl fishery (Seidel & McVea 1982). Despite being less well documented (Raby et al 2011), bycatch of freshwater turtles also occurs in a variety of inland fisheries (Barko et al 2004, Larocque et al 2012a). Turtles typically exhibit high juvenile mortality and delayed sexual maturity (Congdon et al 1993).…”

“…We also evaluated whether male and female painted turtles differed in their physiological and behavioural responses to entrapment. We focused on freshwater turtles that are incidentally captured in a small-scale commercial fyke-net fishery in eastern Ontario, Canada (Carrière et al 2009, Larocque et al 2012a. Upon capture, fishers are required to discard turtles (whether alive or dead) along with other bycatch (e.g.…”