Modified hooks reduce incidental mortality of snapper (Pagrus auratus : Sparidae) in the New Zealand commercial longline fishery

In longline fisheries, decreasing the catch of undersized fish and minimizi ng the rate of gut-hooking over all sizes will reduce incidental mortality, and improve the landed value of the commercial catch. In this study, stand ard Tainawa 16R longline hooks were simultaneously fished for snapper (Pagr us auratus) with the same hook pattern modified by the addition of 20-mm an d 40-mm wire appendages. The experimental design also included three bait t ypes. Gut-hooking rates were markedly lower on modified hooks relative to n ormal hooks. Normal hooks gut-hooked 17% and 30% (pooled across baits) of s napper caught in January and June, respectively, whereas 20-mm modified hoo ks gut-hooked 7% and 12%, and 30-mm hooks gut-hooked only 2% in both season s. overall catch rates were significantly lower on modified hooks, however most of the loss of catch comprised undersized fish and "deads" (unsuitable for export). There was no significant reduction in the weight of export-qu ality snapper landed using modified hooks. Modified hooks reduced both the catch rate and gut-hooking rate of undersized snapper. If it is assulned th at all gut-hooked discards are likely to die, the estimated annual reductio n in discard mortality at the stock li vel would be 78% if 20-mm hook modif ications are used, and 96% if IO-mm modifications are used. These estimates are consistent for scenarios where minimum legal size is set at both 25 cm and 27 cm, however they are based on the assumption that observed catch an d mortality rates are representative of the commercial fishery. (C) 2001 In ternational Council for the Exploration of the Sea.