Characterising Essential Fish Habitat using spatio‐temporal analysis of fishery data: A case study of the European seabass spawning areas

Fish habitats sustain essential functions for fish to complete their life cycle, such as feeding, growing and spawning. Conservation is crucial to maintain fish populations and their exploitation. Since 2013, the spawning stock biomass of the northern stock of European seabass (Dicentrarchus labrax) has been in a worrying state. A series of low recruitments with a persistently high level of fishing has been blamed, raising concerns about the processes involved in seabass reproduction and settlement in nurseries. Here, we characterise seabass spawning areas along the French Atlantic coast using vessel monitoring system (VMS) data. A non‐linear geostatistical approach was applied, from 2008 to 2014, to detect locations where seabass aggregate for spawning. Occurrence maps of spawning distribution were combined into probability maps to quantify the seasonal and inter‐annual variability and to highlight recurrent, occasional and unfavourable spawning areas. We identified three main spawning areas: the Rochebonne Plateau in the Bay of Biscay, the Western English Channel and the North of the Cotentin peninsula in the Eastern English Channel. The correlative link between this geographical distribution and environmental factors was investigated using a Bayesian spatio‐temporal model. The spatio‐temporal structure accounted for the vast majority of the model predictive skills, whereas environmental covariates had a negligible effect. Our model revealed the persistence of the spatial distribution of spawning areas with intra‐ and inter‐annual variability. Offshore areas appear to be essential spawning areas for seabass, and should be considered in spatial management strategies