Reducing the mortality of freshwater turtles in commercial fish traps

Abstract

1. Mortality of air-breathing vertebrates has been recognized for some time as a significant risk in Australian inland fisheries. There has often been conflict between the desires of fishers to maximize catches of their target species and the implementation of effective methods to reduce nontarget by catch. 2. Two trials were conducted to evaluate the effectiveness of modifications to fish traps designed to prevent the capture of freshwater turtles (Emydura macquarii) and to facilitate their release. The first study evaluated the use of 100 mm exclusion rings to prevent turtles entering eel traps. The second study assessed two configurations of a carp trap designed to release the accidental catch of turtles. 3. Eel traps fitted with 100 mm exclusion rings significantly reduced the turtle bycatch, with no significant difference being observed between mean size of eels captured in traps fitted with exclusion rings and traps without rings. 4. The trials on the modified carp trap confirmed that they effectively retained carp and released a majority (77%) of turtles over a 4 h period. Turtles retained in the carp traps were significantly longer than those that found their way out of the trap. 5. This study demonstrates the different approaches that can be taken to achieve a reduction in non-target bycatch associated with traps, and illustrates the importance of exploiting both the physical and behavioural differences of the target and non-target species in order to develop appropriate gear designs that effectively restrict the entry, or facilitate the release, of bycatch species. Copyright © 2004 John Wiley & Sons, Ltd.