The effect of discards and survival rate on the Maximum Sustainable Yield estimation based on landings or catches maximisation: Application to the nephrops fishery in the Bay of Biscay

MSY objectives are being adopted as major fisheries management targets worldwide. However, in fisheries where discards account for an important share of the catches, the yield, effort, and biomass at MSY can be significantly different when accounting or not for discards and thus when, basing the yield estimations on landings or catches. Also whether accounting for a certain survival rate, of discards can lead to different MSY targets estimates. Hence, both decisions have important, implications on catch and effort reduction recommendations, and consequently on the quota, calculations for fisheries managed by quotas. Results from the Bay of Biscay nephrops fishery confirm, that the optimal exploitation level can vary significantly when optimising for catches or landings, and, by assuming a certain survival rate of the discards. By doing this, the present study also allows to, explore the basis to clarify the definition of MSY in fisheries where discarding takes place.