Climate variability and recruitment success of European hake (Merluccius merluccius L.) in NW Africa

Recently it was stated a strong dependence of European hake abundance with climate variability in NW Africa. This relationship was explained by the North Atlantic Oscillation (NAO) driving the upwelling temporality and its geographic coverage, which could be responsible of changes in survival rate during early life stages of this species. Following this hypothesis, this work focuses on the relative importance of climate variability on recruitment dynamics of European hake. Interannual variability of recruitment success were analyzed through two types of time series: (i) from monthly and annual length distribution fishery data (1982-1999) of Spanish trawling fleet that worked under Spanish or European-Moroccan fishery agreements and (ii) recruits annual abundance from scientific Moroccan surveys (1982-2004). The time series were compared with the annual smoothed NAO index to evaluate the type of relationship, persistence and their relative contribution as a variation source of recruitment success. The recruitment to the fishery took place during all year with peaks in spring and summer, but the seasonal component was weak. The time series were in synchrony with NAO index of the previous year and showed strong positive correlation. The variation of recruitment success explained by NAO was 25 to 82 % depending on time series size. The main NAO effect in recruitment dynamics was the widening-contraction of Recruitment Window. During NAO+ phase several success cohorts were recruited by year, while in NAO- the success cohorts were scarce and weak. The climate signal in recruitment dynamics of European hake was robust, recurrent and persistent independently of fishing effort

Occurrence and distribution of Black hakes Merluccius senegalensis Cadenat 1950 and Merluccius polli Cadenat 1950 off Mauritania

There are two species of hakes distributed in waters off Mauritania, that are commonly known as black hakes, Merluccius senegalensis Cadenat, 1950 and Merluccius polli Cadenat, 1950. Both species overlaps their bathymetric distribution on the continental shelf and slope where they are fished by Spanish trawling and bottom longliner fleets, which implies mixed fishing statistics. During 2003 and 2004 there were conducted several scientific watching campaigns onboard of trawler ships as well as two experimental campaigns onboard in a longliner ship. Based on obtained data, in the present work there are analyzed general aspects of time-space variation of both species population. It is stated a dependence distribution on depth. M. senegalensis was found in poor quantities deeper than 500 m. The overlapping between both species took place from 150 to 500 m, and M. polli were caught by trawling in deepest waters, more than 900 m. M. polli was the predominant specie of the trawling fleet catches (88 % in weight) that fishing on deep waters, whereas M. senegalensis was the most abundant specie into the longliners fishing area, reaching 67 % of the catches. The specimens of both species increase in size with depth, being the average lengths of M. senegalensis larger than M. polli . It was found significant difference between the length frequency distributions of both species in all the strata of depth

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.Publicado

NAO related small pelagic fisheries fluctuations off Morocco and Senegal

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