Survivability of discarded Norway lobster in the bottom trawl fishery of the Bay of Biscay

Abstract

Abstract In the context of the landing obligation set by the new Common Fisheries Policy (CFP), Norway lobster Nephrops norvegicus was identified as a species likely to have high survival rate when discarded in the bottom trawl fishery of the Bay of Biscay. Previous studies in this area reported a survival rate between 30% and 51%, but the experiments were done on a limited monitoring period and the seasonal variations were not investigated. This study was designed to obtain a reliable value for survival rate after a 14-day monitoring period in onshore tanks allowing considering delayed mortality. The study also tested the effect on the survival rate of using a discarding chute system, a sorting device that was made mandatory on the 1st of January 2017 for Nephrops trawlers in the Bay of Biscay. This device, which enables fishermen to discard undersized Nephrops back to the sea while sorting, led to an increased average survival rate (51.2%) compared with the standard sorting practice (36.9%). The impact of biological, environmental and fishing operation related variables on survival from the first day of captivity to the end of the monitoring period was examined using a generalized linear model. The results of the GLM indicate that injuries, season and duration of the air exposure, significantly influence the survival from the 1st day of captivity to the end of the monitoring period. The survival rate was higher for non-injured Nephrops as well as for Nephrops that have undergone short air exposure, in summer and autumn.