The impact of turtle excluder devices and bycatch reduction devices on diverse tropical marine communities in Australia's northern prawn trawl fishery

Abstract

In 2001, paired-trawl comparisons were made during prawn trawl operations to assess the effect of turtle excluder devices and bycatch reduction devices on a range of species groups caught in tropical Australia. This study is one of the first to evaluate the commercial use of these devices in a tropical fishery. Nets with a combination of a turtle excluder device and bycatch reduction device reduced the catches of turtles by 99%, seasnakes by 5%, sharks by 17.7%, rays by 36.3%, large sponges by 85.3%, and small bycatch by 8%, however, these results were largely attributable to the influence of the turtle excluder devices. Nets with both devices also reduced the catch of commercially important prawns by 6%, but the proportion of soft and damaged prawns was reduced by 41%. The combination of these devices had no measurable impact on catches of any of the three byproduct species groups: Thenus spp. (Moreton Bay bugs), Teuthoidea spp. (squid) and Amusium pleuronectes (scallops). Turtles excluder devices reduced the numbers of larger sharks and rays (>1 m) by 86% and 94%, respectively. They did not reduce the total number of sawfish caught, but did reduce the number of the most commonly caught species – the narrow sawfish ( Anoxypristis cuspidata) – by 73.3%. Upward- and downward-excluding turtle excluder devices performed about equally for most species groups, although upward excluders were more effective for sharks and less effective for large sponges. The performance of BRDs was poor for most groups and could be improved by using them in more effective positions such as closer to the codend catch. The use of these devices is a major step towards ensuring the long-term conservation of many species, especially endangered sea turtles and vulnerable elasmobranchs. As fishers become more experienced in their use, we are optimistic that the fishery's impact on bycatch will reduce even further.