Although previous studies included video observations of turtles to determine whether they interacted with internal BRDs as expected ( Lowry et al. Thus, BRDs contained entirely within the net should be generally desirable ( Lowry et al. Ease of setting modified nets and the ability to set in variable conditions (water depth, wind, current) are often cited as useful qualities by fishers ( Nguyen et al. Also, reliance on the water surface as the escape route limits the depth for net setting, which can be a concern for fishers ( Nguyen et al. These devices are effective for some species, but their efficacy at freeing multiple species of turtles has rarely been documented ( Larocque et al. Net modifications designed for bycatch escape are often external, chimney-style devices, where a tube of mesh joins the terminal compartment of the net to the surface of the water, allowing the amphibious turtles to escape while aquatic fish are retained ( Roosenburg et al. Escape BRDs can be placed to take advantage of this spatial segregation between bycatch species and target species.īecause of the threat that fisheries pose to freshwater turtles, a number of escape BRDs have been developed to improve gear selectivity and to reduce incidental capture ( Wood 1997 Bury 2011 Larocque et al. For example, air-breathing species, such as freshwater turtles, typically occupy higher positions in entrapment gear as a result of their surface-seeking behavior than do targeted fish species ( Lowry et al.
Differences in behavior can be co-opted as selective criteria to be used independently or in concert with morphological differences to reduce bycatch. Quantification of animal behavior and the application of behavioral principles is an underutilized tool in conservation biology ( Caro 1998 Sutherland 1998 Broadhurst 2000). However, in fisheries where morphology alone does not fully discriminate between target and bycatch, the inclusion of behavioral differences may help distinguish between the two ( Broadhurst 2000 Cairns et al.
In the case of entrapment gear, however, escape BRDs can be used in addition to, or instead of, exclusion BRDs.Įscape BRDs are most effective when there are morphological differences, particularly differences in size, between target and bycatch species. If this is the case, smaller individuals and smaller species can still be collected, which can result in demographic, population, and community shifts ( Roosenburg et al. In fisheries where target and bycatch species overlap in size, exclusion of bycatch can be incomplete ( Fratto et al. Exclusion BRDs are particularly effective when bycatch animals are larger than the target animals ( Broadhurst 2000 Hall et al. Exclusion BRDs typically comprise rigid grids, bars, or rings to limit the size or shape of organisms that can enter the net ( Bury 2011). The avoidance of bycatch through BRDs often focuses on devices that prevent the capture of an individual, referred to as exclusion BRDs. Modification of fishing equipment with bycatch reduction devices (BRDs) can improve gear selectivity by excluding nontarget species or enabling bycatch to escape ( Broadhurst 2000). The use of behavioral observation to guide the development of bycatch reduction devices may provide an extra tool for managers to increase selectivity and maintain sustainable harvests of target fish. The escape device developed in this study can potentially be used in the local fishery or modified for other fisheries. Escape devices can be used as a key component of a bycatch reduction program and be particularly effective when paired with exclusion bycatch-reduction devices. Our preliminary field trials indicated that modified fyke nets decreased the capture rate of turtles relative to unmodified nets.
When turtles were introduced into modified nets, escape was rapid (mean of 12.4 min), with 100% escape for map Graptemys geographica and musk turtles Sternotherus odoratus and 94% escape for painted turtles Chrysemys picta. We also used behavioral observations to identify areas of the net most used by turtles, thus revealing the most logical placement for an escape bycatch-reduction device. We employed quantitative and qualitative behavioral observations (with action cameras deployed underwater) to develop a new, collapsible, escape bycatch-reduction device that mounts internally in the terminal end of a fyke net.
Fyke nets can be equipped with bycatch reduction devices that enable the escape of turtles before they drown. The drowning of freshwater turtles following incidental capture in fishing gear has the potential to cause population declines.
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