Large Hooks Reduce Catch-and-Release Mortality of Blue Cod Parapercis colias in the Marlborough Sounds of New Zealand

Abstract

An experiment was conducted in early summer 1995 to determine the survival rate of sublegal-size (<33 cm total length) blue cod Parapercis colias after being captured and returned to the sea by amateur fishers using two types of hooks (6/0 and 1/0). At the same time, commercial cod pots captured blue cod for use as a control group. As fish were caught, they were subjected to either good or poor handling techniques and then placed into holding pots built specifically for the experiment. These were lowered to the sea floor and sequentially monitored during daylight hours for 2 weeks. No mortality of blue cod occurred with the 6/0 hooks, but fish caught using 1/0 hooks suffered 25% mortality by the end of the experiment. No control fish died during the experiment, and the type of handling technique used had no detectable effect on blue cod survival. The fact that all mortality occurred within 26 h, combined with observations of fish behavior, suggests that mortality was induced by blood loss rather than disease. The location of the hook wound was related to hook size, small hooks lodging in the gut or gill usually proved fatal. These findings suggest that the mortality of released blue cod would be minimized if fishers used larger rather than small hooks. The management of blue cod by size limit regulation is discussed in relation to these findings.