Influence of the Climatic Oscillations on the Sardine off Northwest Africa during the period 1976-1996

– Studies on the impact of climate change on exploited marine fishes are numerous. However, the response of fish stocks to these effects is hard to predict, due to the inherent uncertainty in these models, and the lack of knowledge of the biological response of species in short time periods. Thus, some authors have modelled the response of marine species to largescale climate phenomena. The main aim of the current study is to analyze the possible effect of the main large-scale climate indices: Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO), and Arctic Oscillation (AO) and Southern Oscillation Index (SOI) (as measured to El Niño/La Niña episodes) on the variability of the NW African sardine (Sardina pilchardus) stock. The sardine fishery data has its origin in the fishing activity of Spanish purse seine fleet in NW Africa from 1976 to 1996 developed within the Fishery Agreement between Spain-Eu and Morocco. These fisheries data refer to one FAO statistical area along the African coast between the parallels 29°N and 26°N. The results indicate that there is an effect driven by AO affecting sardine relative abundance in the study area, at least for the period 1976-1996. Moreover, this relation between AO and sardine relative abundance could involve the Sea Surface Temperature. AO CECAF FISHERIES SMALL PELAgIC 72 J.C. BÁEZ, M.T. g. SANTAMARÍA, A. gARCÍA, J.F. gONZÁLEZ, E. HERNÁNDEZ, F. FERRI-YÁÑEZ Vie milieu, 2019, 69 (1) the Western coast of Africa, sardines are an important resource for the countries in the region. The main aim of the current study is to contribute to the knowledge on the possible effect of climate variability described by the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and El Niño Southern Oscillation (ENOS) on the Sardina pilchardus fishery along NW African coast, both in regard to the variability of this resource, and in its possible biological implications. MATERIAL AND METHODS The sardine fishery data source is the fishing activity of Spanish purse seine fleet in NW Africa from 1976 to 1996, developed under different Fisheries Agreement between Spain-Eu and Morocco. These fishery data refer to FAO Zone B (along the African coast between the parallels 29°N and 26°N). The agreement ended in 1999, but from 1996 to 1999 was mandatory fishing in Zone C (south of 26oN). Sardine stocks are highly influenced by the eastern boundary upwelling system (EBuS) of the Canary Current, constituting the most abundant small pelagic resource in the study area. We consider that CPuE, in this particular scenario, reflects the local relative abundance or at least available biomass of sardine stocks. The annual CPuE of Spanish statistics available during this period was used. These data use fishing days as fishing effort unit (FAO 2016b). Monthly values of the AMO, AO, NAO and SOI index were downloaded from the website of the National Oceanic and Atmospheric Administration: http://www.cpc. noaa.gov/. Firstly, we analyzed the time series for each variable. In order to identify periodicity or autocorrelation, we searched for common time trends and cyclicity in the time series using spectral analysis. Spectral analysis was performed with the software PAST (available from web site: http://folk.uio.no/ohammer/past/) (Hammer et al. 2001, Hammer & Harper 2006). Different curve regression models were applied using the CPuE of sardine versus the climatic oscillations used as independent variables. We selected the best fit among several significant regressions when different degrees of freedom were involved, in accordance with the high-