The unfulfilled potential of fisheries selectivity to promote sustainability

The recent reform of the Common Fisheries Policy (CFP) in Europe highlights the need for improvements in both species and size selectivity. Regarding size selectivity, shifting selectivity towards older/larger fish avoids both growth and recruitment overfishing and reduces unwanted catches. However, the benefits to fish stocks and fishery yields from increasing age/size-at-selection are still being challenged and the relative importance of selectivity compared to that of exploitation rate remains unclear. Consequently, exploitation rate regulations continue to dominate management. Here, an age-structured population model parameterized for a wide range of stocks is used to investigate the effects of selectivity on spawning stock biomass (SSB) and yield. The generic effect of selectivity on SSB and yield over a wide range of stocks is compared to the respective relative effects of exploitation rate and several biological parameters. We show that yield is mainly driven by biological parameters, while SSB is mostly affected by the exploitation regime (i.e. exploitation rate and selectivity). Our analysis highlights the importance of selectivity for fisheries sustainability. Catching fish a year or more after they mature combined with an intermediate exploitation rate (F ≈ 0.3) promotes high sustainable yields at low levels of stock depletion. Examination of the empirical exploitation regimes of 31 NE Atlantic stocks illustrates the unfulfilled potential of most stocks for higher sustainable yields due to high juvenile selection, thus underscoring the importance of protecting juveniles. Explicitly incorporating selectivity scenarios in fisheries advice would allow the identification of optimal exploitation regimes and benefit results-based management.