D.S. Heales

Validating ecological risk assessments for fisheries: assessing the impacts of turtle excluder devices on elasmobranch bycatch populations in an Australian trawl fishery

Demonstrating ecological sustainability is a challenge for fisheries worldwide, and few methods can quantify fishing impacts on diverse, low value or rare species. The current study employed a widely used ecological risk assessment method and incorporated new data to assess the change in sustainability of species following the introduction of Turtle Excluder Devices (TEDs) in Australia’s Northern Prawn Fishery (NPF). Population recovery ranks changed for 19 of the 56 elasmobranch species after the introduction of TEDs, with nine species showing an increase in sustainability. Unexpectedly, ten species showed a decrease in sustainability. This was due to TEDs successfully excluding large animals from the catch, resulting in a lower mean length at capture, which reduced the recovery ranks for two criteria relying on length data. This falsely indicates that TEDs increase the impact on pre-breeding animals, thus reducing the recovery potential of these species. The results demonstrate that existing attribute-based risk assessment methods may be inadequate for reflecting even the most obvious changes in fishing impacts on bycatch species. Industry and management can benefit greatly from an approach that more accurately estimates absolute risk. The development and requirements of a new quantitative risk assessment method to be developed for the NPF, and applicable to fisheries worldwide, are discussed.