Climate variability and fisheries of black hakes (Merluccius polli and Merluccius senegalensis) in NW Africa: A first approach

Fish populations and fisheries fluctuations are closely linked to climate dynamics through environmental variability that determines distribution, migration, and abundance. Fisheries science has largely focused on the larger fisheries of the northern hemisphere, some of which fluctuate at decadal time scales and show patterns of synchrony with low frequency signals, as reflected by climatic indices such as the North Atlantic Oscillation (NAO). However, there is limited information on these patterns for the NW African coast, where important international fisheries have been established for decades. In order to improve our understanding of the impacts of climate variability (in particular the NAO) on black hake dynamics in northwest Africa, we used catch-based relative abundance indices from commercial fisheries off Mauritania and Senegal as dependent variables in correlation analyses with the NAO index. Then we tested the mechanistic dependence between the NAO index and north–south (v) component of the wind stress as a proxy of upwelling variability. Black hake abundance was highly and negatively correlated with the NAO index, with a time lag of 3 years. The NAO explained around 40 to 50% of abundance variability between 1960 and 2003. At the same time, the wind stress fields were positively correlated with NAO during the same year, which was responsible for 53% of their variability. In contrast to what we expected, these results suggest that black hake abundance is inversely related with intensified and extended upwelling processes along the Mauritanian and Senegalese coast, causing the cold oceanographic season to extend more southwards than normal.