Adverse consequences of stock recovery: European hake, a new “choke” species under a discard ban?

Many commercial fish stocks are beginning to recover under more sustainable exploitation regimes. In this study, we document the temporal and spatial changes in one remarkable example of stock recovery: northern European hake (Merluccius merluccius). Analysing data from several scientific surveys, we document a dramatic increase in estimates of biomass between 2004 and 2011 throughout the larger area now occupied by the stock. The largest increase occurred in the North Sea, where hake have been largely absent for over 50 years. Spatio-temporally resolved commercial landings show that high densities occur in the North Sea only between April and September, suggesting a density-dependent seasonal habitat expansion to suitable temperature and depth conditions. These changes have implications for the management of the stock which are discussed. Notably, if discards are banned as part of management revisions, the relatively low quota for hake in the North Sea will be a limiting factor (the so-called ‘choke’ species) which may result in a premature closure of the entire demersal mixed fishery in the North Sea, jeopardizing many commercial fisheries in the region. This example of the unforeseen consequences of improved stewardship highlight the need for a more holistic, regional and responsive approach to managing our marine ecosystems.