Summary
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.
Methodology
After consultations in fall 2008, we used fishing practices employed by local commercial fishers. Newboro Lake sampling was conducted with hoop nets used by local commercial fishers, consisting of eight 0.8-m diameter wooden hoops positioned 0.5 m apart. There were three throats per net, on the first, third and fifth hoop of the net. Each net had two wings (2.9 m long and 0.8 m high) and a lead (11 m long and 0.8 m high) attached to the front hoop. We sampled Lake Opinicon using similar nets that contained seven 0.9-m diameter steel hoops positioned 0.5 m apart. There were two throats per net, located at the second and fourth hoops. Each net had two wings (4.5 m long and 0.9 m high) and a lead (10.7 m long and 0.9 high) attached to the front hoop. All nets, wings and leads were constructed with 5.08-cm stretch nylon mesh. To emulate the commercial fishery, all nets were set in tandem by adjoining two hoop nets by their leads, with the net openings facing each other and extending the wings to a 45° angle from the entrance of the net (Fig. 1).
Newboro Lake fishing occurred in spring of 2009, while Lake Opinicon fishing was during spring and fall of 2010. In spring, fishing began after ‘ice-off’ (early April) and continued until the end of the legal fishing season (June 20). In fall, fishing began just after the beginning of the legal fishing season (i.e. first Monday of September) and ended on October 2. In both lakes, we set nets in vegetated shallows (1–1.75 m depth), and recorded water temperature when setting and lifting. In the commercial fishery, hoop nets are completely submerged. In Newboro Lake, however, we placed plastic jugs in the end of each net to create airspaces for air-breathing fauna. In Lake Opinicon, we fished using nets with and without airspaces, and net set durations varied (8–48 h) according to water temperature to prevent mortality of turtles, specifically species at risk. Set durations decreased with warmer water and were based on reduced anoxia tolerance and survival durations found by Herbert & Jackson (1985). To determine the extent of fish mortality in hoop nets of different set durations, we set nets in Newboro Lake for either 2 or 6 days. For both durations, nets were set for 2 days allowing animals to enter, and either lifted (2-day set) or were closed off by tying a wing in front of the net entrance to prohibit the entrance of any other organisms and left for 4 more days (6-day set). All non-fish bycatch were removed from the nets prior to closing the net off for the 6-day set. This allowed for a comparison of fish caught and retained in the nets for 0–2 and 4–6 days. In all cases, after the set period we lifted the tandem net and all organisms were identified to species and tallied. Any mortality was recorded.