Evolution de l’activité des flottilles ciblant le Lieu noir en Mer du Nord. Quels impacts sur les captures par unité d’effort de pêche de la flottille de tuning ?

The 2011’s stock assessment pointed out an important decrease in the biomass of the North Sea saithe within 2009, while it was regarded for several years as a symbol of the sustainable management of the North Sea stocks. Meanwhile, an increasing spatial competition with other fleets has been reported since 2008 in the North of Shetland, where the majority of catches occur. This study was carried out to confirm and assess the extent of the changes in the distribution of fishing effort and to define if it could be linked to the collapse of the Catch Per Unit Effort (CPUE) in 2009. Exploratory analyses were held to calibrate the tuning fleet and to identify areas of the North Sea specific to certain species. These factors were then used as explanatory variables to assess the impact of the fleet’s dynamics on its CPUE. Due to the large number of low catches in the data, standardization was conducted using a double generalized linear model. The study showed that the lack of calibration of the French tuning fleet tends to underestimate its CPUE. It also highlighted an expansion of the fishing effort’s spatial distribution and a decrease in the stock abundance in 2009, which, coupled with a renewal plan of the fleet by less efficient vessels, resulted in a hyperdepletion of the CPUE of the French tuning fleet. On the other hand, the representativeness of Obsmer sampling was studied for the first time for North Sea saithe, and numbers-at-ages were raised using COST. The results were compared with those from the current raising procedure. Data were reliable when a sufficient number of sampling was carried out, giving a wide range of possible uses of Obsmer data.