Discarded Fish: From on Deck Vitality Assessment to Survival after Release

Survival of discarded species has become an important concern in Europe since the European Union reformed the Common Fishery Policy and introduced a landing obligation. Under this obligation, no quota-managed species can be discarded unless a high potential for discard survival has been demonstrated. European plaice appears to be a good candidate for such an exemption, and there is a pressing need to quantify discard survival and to identify the factors that influence it for this species. To address these objectives for plaice discarded in the Eastern English Channel trawl fishery, we used approaches based on vitality assessment and Reflex Action Mortality Predictors. These health indicators (HI) have been demonstrated to be good proxies for discard survival across a broad suite of species and HI data are relatively easy to collect. First we used models for ordinal data to explore the relevant technical, physical and biological factors that were associated with HI in plaice, and by proxy with survival. Then we used results from discard survival experiments and HI monitoring in the fishery to estimate a discard survival rate and associated uncertainty using error propagation methods.