Spatiotemporal variation of fishery patterns, demographic indices and spatial distribution of European hake, Merluccius merluccius, in the GSA 01 and GSA03

European hake, Merluccius merluccius, is one of the most commercialized species in the Alboran Sea and elsewhere in the Mediterranean Sea. In the Alboran Sea, European hake stocks are regularly assessed as shared stocks. However, there are no scientific evidences for shared or separate any stock in this area yet. As in most stocks on earth, boundaries of stocks (and the geographical subareas in the case of the Mediterranean Sea) have been established by the General Fisheries Commission for the Mediterranean, GFCM, based on political and statistical considerations rather than biological factors. In this respect, the multidisciplinary project TRANSBORAN, was built with the overall aim of reviewing stock units boundaries of the Alboran Sea stocks of the most relevant species, including European hake. In this study and in the framework of the aforementioned project, published information and available data on European hake in GSA 01 (Spain) and GSA 03 (Morocco) are compiled to analyze the spatiotemporal variation of fishery patterns, demographic indices and length distributions of this species applying several methodologies. First, generalized additive models and dynamic factor analysis were applied on monthly time series of Landings Per Unit Effort (LPUE) of 13 ports in the study area to describe the seasonal and inter-annual variability and underline common trends between the two GSAs. Second, length distribution of the species was compared between GSAs and years. Finally, spatial distribution metrics in longitude, latitude and depth were calculated for both GSAs to compare the spatial distribution of the species and then examine their temporal variability and the potential density-dependent influence. The present study shows that there is a clear seasonal and inter-annual variability on hake LPUE mainly associated to two common trends. The first is associated only to northern ports of Alboran evidencing a south-north difference. The second is associated only to eastern ports of both Alboran shores. Spatial metrics showed marked density-dependent inter-annual fluctuations in hake distributions, which were asynchronically related between GSAs, suggesting potential but intermittent linkages between GSAs driven by early life stages connectivity. Significant differences are also observed in hake length distribution within and between GSA 01 and GSA 03. The results of this study shed new light on spatial dynamics of European hake population at the Alboran Sea and may have implications to provide scientific basis to future definition of the hake population structure and the differentiation of stock units in the Alboran Sea.