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



Sarah M. Larocque, Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada.



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.