Variable post-capture condition estimated by visual assessment for key recreational species discarded in a nearshore marine charter fishery off eastern Australia

Abstract

Many fish species caught in recreational fisheries are released after capture due to regulations or fisher preference. In regions where large proportions of the catch are released, assessing ‘post-capture survival’ (PCS) is essential for comprehensive stock assessments and sustainable management. Here we present a case study for the development and application of a simple semi-quantitative approach to provide ‘post-capture body condition’ (PCC) indices using visual assessment in a coastal boat-based angling fishery, providing an informative descriptive precursor to quantifying actual PCS. Assessment indices and scores were developed from published information on factors shown to affect PCS of the focal species, so that estimated PCC was indirectly related to survival. More than 2000 individuals of 18 species were visually assessed by trained observers prior to release and overall PCC estimated. For commonly released species, estimates of PCC were highly variable and primarily determined by the degree of observed barotrauma. Estimated PCC was highest for Bluespotted Flathead, Mahi Mahi, Yellowtail Kingfish and Pearl Perch, lower for Grey Morwong and Snapper, and lowest for Teraglin. For Grey Morwong and Teraglin, increasing capture depth also significantly decreased PCC. Body length and water temperature did not have a significant effect on the PCC of any species. Whilst true survival of each individual is not determined here, the approach described provides an efficient basic assessment of PCC which combines multiple factors into a single estimate providing an important descriptive precursor to inform future work using direct approaches to quantify actual PCS. Such studies may also improve the utility of this metric by defining the functional relationship between PCC scores and PCS. This approach can be easily implemented as a preliminary standard practice where there is an intention for PCS data to be collected to evaluate the effectiveness of management, or for stock assessments to account for indirect fishing mortality.