The capture of non-target species is a conservation issue in many commercial fisheries. Bycatch reduction devices (BRDs) are commonly used as mitigation tools to improve selectivity of fishing gear and thus reduce bycatch. The aim of this paper was to refine a simple BRD to exclude 4 species of freshwater turtles from commercial fyke nets in a fishery in eastern Ontario, Canada, that targets a variety of fish species. We tested the efficacy of modified exclusion devices (vertically oriented exclusion bars and a constriction rectangle) using an adaptive approach including in situ observations, controlled behavioural experiments and field trials. In situ observations made by camera were used to estimate turtle catchability and to document turtle behaviour during net interactions, which was used to inform BRD design and placement. In controlled behavioural experiments, the passage rates of target fish (i.e. sunfish), bycatch fish (e.g. game fish) and turtles across a modified net throat suggested that a 5 cm constriction rectangle should be suitable for reducing bycatch in this fishery; turtles readily turned sideways to pass through larger openings. Paired field trials indicated that a 5 cm constriction rectangle reduced turtle bycatch for all species. The constriction rectangle also reduced captures of non-target game fish. In controlled behavioural experiments, there was little evidence of a reduction in catches of target sunfish; however, in paired field trials, there was a 23.4% reduction in sunfish catches. We recommend the use of a 5 cm constriction rectangle for fisheries targeting sunfish in areas where freshwater turtles are present.
The study was conducted on Lake Opinicon and at the Queen’s University Biological Station (44° 34’ N, 76° 19’ W) approximately 100 km southwest of Ottawa, Ontario, Canada. Lake Opinicon is a shallow (mean depth of 2.8 m) mesotrophic lake with a surface area of 780 ha (Agbeti et al. 1997).
Nets and net set methods used in this study were the same as those presented by Larocque et al. (2012a) and mimic those used by commercial fishers in eastern Ontario. Briefly, we used fyke nets constructed of 7 structural rings each with a diameter of 0.91 m attached together with no.15 knotted nylon, 1 inch (2.54 cm) square mesh (2 inch [5.08 cm] stretch; Christiansen’s Nets Company). On the second and fourth rings is a throat that directs organisms into the cod end of the net and minimizes escape. These nets were set in pairs connected mouth to mouth by a lead net 10.7 m long and 0.91 m tall, and each net also had 4.6 m long wings set at ~45° angle all made of the same material. The nets were set near shore in shallow water (1 to 2.5 m deep), equipped with floats to provide an airspace, and left to fish for approximately 24 h.
GoPro Hero cameras (Woodman Labs) pointing out towards the mouth were deployed inside 98 fyke nets (Fig. 1) from 12 June 2011 to 20 June 2012 and programmed to take 1 high-resolution photo every 5 s for approximately 3.5 h. We reviewed the photos to record the number of interactions/observations for each species of turtle. The observations per unit effort (OPUE) were then compared to the capture per unit effort (CPUE) of the same net over the total soak time. Qualitative observations were also made of the way turtles approach the nets and the way they move around the mouth of the net to inform BRD design and refinement.