Comment on stock assessment of eels in the Baltic by Westerberg and Wickström (2015): Do we need more unknowns?

Abstract

European eel (Anguilla anguilla) is considered as critical endangered and even under the best circumstances it may take decades before the stock recovers. Estimation of eel escapement biomass, Bescapement, is of critical importance to evaluate management schemes and to predict the recovery potential for the eel stock. Westerberg and Wickström (2015. Stock assessment of eels in the Baltic: reconciling survey estimates to achieve quantitative analysis. ICES Journal of Marine Science, 73: 75-83) attempt to estimate potential Bescapement based on the assumptions that all elvers at the entrance of the Baltic also migrate into the Baltic Sea and that natural mortality is low under the whole growth stage (close to 0.02 at the age of 10 years and older). As a consequence, Westerberg and Wickström estimated the present potential Bescapement at ∼10-20 000 tonnes and fishing mortality close to 0.05-0.10, while it was also suggested that other sources of anthropogenic mortality may reduce the actual escapement to unknown levels. Here we argue that these conclusions are entirely speculative and contradicted by tagging experiment and fishery data, which instead indicate a much higher fishing mortality (mortality induced by legal professional fishery) rates and a considerably smaller eel biomass.