Reducing the mortality of discarded undersize sand whiting Sillago ciliata in an estuarine seine fishery

Abstract

A field experiment was done to determine the effects of mesh size in the bunt and codend of an estuarine beach-seine net on the meshing (gilling) and discarding of undersize sand whiting Sillago ciliata (Sillaginidae). Four mesh sizes were examined: 45 mm, 50 mm, 57 mm and 64 mm, in an alternate-haul experiment in the Clarence River, New South Wales, Australia. A laboratory experiment was also done to determine the mortality of sand whiting after becoming meshed in seine nets. The currently allowed mesh size (50 mm) catches a large proportion of undersize sand whiting that become meshed in the netting and are subsequently discarded. The laboratory experiment showed that ~40% of these fish may die within a few weeks whereas no unmeshed fish die. In contrast, the 57 mm mesh size meshed few undersize sand whiting yet retained almost the same number of legal-sized fish as the 50 mm mesh. Hence, the maximum mesh size allowed in the bunts of nets used in this fishery should be raised to 57 mm to allow the escape of large numbers of undersize sand whiting that are currently being caught, meshed and discarded in a condition that leads to significant mortality.