Evaluating relative impacts of recreational fishing harvest and discard mortality on Murray cod (Maccullochella peelii peelii)

Murray cod Maccullochella peelii peelii support popular recreational fisheries in Australia. Catch and release of Murray cod is common due to regulations and a developing trend of voluntary angler release of harvestable fish, but no previous studies have investigated discard mortality of released fish. We estimated discard mortality by measuring post-angling survival of angler-caught wild Murray cod. Angled fish were monitored for five days after hooking, and overall survival rates of 98% were observed. We explored implications of catch and release as a fishing mortality source by comparing our results to roving creel survey estimates of harvest from six fisheries. We applied the maximum likelihood mortality estimate and upper 95% confidence interval to creel survey estimates of the number of Murray cod that were released in the fishery to estimate the total deaths resulting from catch and release mortality. Estimated ratios of deaths from discard mortality to harvest indicated that high numbers of released fish could contribute as much or more to fishing mortality as harvest in some systems. Future Murray cod research should aim to estimate annual exploitation rates to determine the population-level impacts of fishing mortality, and thus, allow effects of hooking and harvest mortality to be considered in future regulation decisions.