Northward migration of small pelagic fish off West Africa : the barrier of the Sahara Bank in the context of climate change [résumé]

2015

Colloque

Brochier Timothée, Machu Eric, Pecquerie Laure, Thiaw M., Mbaye B.C., Braham C.B., Ettahiri O., Charouki N., Auger P.A., Brehmer Patrice

PREFACE-PIRATA-CLIVAR Tropical Atlantic Variability Conference

[s.l.] : IRD, 2015, p. 38

PREFACE-PIRATA-CLIVAR Tropical Atlantic Variability Conference, Cape Town (ZAF), 2015/08/25-27

The Northwestern coast of Africa shelters is a wide part of the Canary Current Large Marine Ecosystem (CCLME). Small pelagic fisheries are of major interest for the economics of the coastal states and food security of Sahel region. Furthermore, small pelagic fish are keystone species for the energy transfer from primary production to large predators in the upwelling ecosystems. Along the CCLME system, different small pelagic fish species dominates the catch. In the Northern part of the CCLME combining seasonal and permanent upwelling, Anchovies (Engraulis encrasicolus) and sardines (Sardina pilchardus) dominate the catches from Gibraltar to Cape Blanc, while in the Southern part, from Cape Blanc to Cape Roxo, where occur a seasonal upwelling, the main small pelagic species is the round sardinella (Sardinella aurita). Understanding the factors responsible of this ecological barrier is essential to address the potential effects of climate change on the spatial patterns of fish distribution. We address this issue using a new individual based bio-physical model for round sardinella where the environmental forcing is taken from archived hydrodynamical and bio-geochemical simulations of the upwelling system from 10 to 35°N, with a 1/12° spatial resolution. The model reproduces the main patterns of S. aurita seasonal migrations and inter-annual fluctuations. The sensitivity tests performed with the model suggest that the northward limit of the S. aurita population is strongly related on the strength of the southward current in the Sahara Bank region. More generally, the collective fish swimming capacity may be a determinant factor for small pelagic fish species presence over the Sahara bank. North of 26°N, our bio-energetic model suggest that the combination of food limitation and low temperatures prevent the growth and maturation of S. aurita individuals. The observed decreasing trends of the wind intensity and the increasing catches of sardinella reported South of Morocco and in the Canary Islands fit well with such outcome, and should be considered in climate change scenario.

Climatologie / Météorologie [032CLIMET] ; Milieux physico-chimique [032MILPHY] ; Poissons [034BIOVER01]

Fonds IRD [F B010091462]

fdi:010091464