New insights on European hake biology and population dynamics from a sustained tagging effort in the Bay of Biscay

de Pontual, H., Jolivet, A., Garren, F., and Bertignac, M. 2013. New insights on European hake biology and population dynamics from a sustained tagging effort in the Bay of Biscay. – ICES Journal of Marine Science, 70: . Following a pilot experiment that fundamentally challenged the knowledge of European hake life traits (growth and age at first maturity), a sustained tagging effort was carried out in the Bay of Biscay from 2004 to 2007. Out of 27 690 fish tagged between 2002 and 2007, 1199 (4.3%) have been recovered to date. These data have permitted a refinement of the growth parameters of the species, analysis of interannual variability, improved understanding of movements and migrations, and an examination of natural (M) and fishing mortality (F). Both L∞ and K of a von Bertalanffy growth model could be estimated using a robust non-linear regression procedure. Growth varied significantly between years, which is likely related to variation in environmental factors such as temperature. Data did not reveal seasonal movements of fish perhaps because of poor tag return rates from offshore fleets. However, results clearly revealed homing behaviour and/or inshore residency. Confounding factors hindered the estimation of mortality, which resulted in high estimates of M. The outcomes of this experiment led to substantial changes in the stock assessment conducted by ICES and call into question the findings of previous studies that have used erroneous age-based data to address topics on the ecology and dynamics of this species.