The importance of retention processes in upwelling areas for recruitment of Octopus vulgaris: the example of the Arguin Bank (Mauritania)

The relationship between recruitment of octopus (Octopus vulgaris) populati ons and environmental conditions off the Arguin Bank (Mauritania) in the ma in nursery ground was investigated between 1990 and 1996. Three environment al indices (coastal upwelling intensity, coastal retention and wind-induced turbulence indices) are derived from satellite infrared imagery (METEOSAT) and from the GOADS (Comprehensive Ocean-Atmosphere Data Set) data to quant ify the coastal retention process and productivity, both believed to be imp ortant factors for recruitment success. The octopus recruitment index as we ll as environmental indices fluctuate annually and seasonally. Linear regre ssion and generalized additive models (GAM) are used to relate recruitment indices and the environmental conditions prevailing during the early-life p lanktonic stage, known to be the main critical period of the octopus life c ycle. Coastal retention especially appears to he a key factor for recruitme nt success. Owing to seasonal variations in enrichment and mixing processes , larvae benefit from retention in the spring but are negatively affected b y a breakdown in retention in the autumn. Increasing upwelling intensity is beneficial for octopus recruitment, as the Arguin Bank limits the detrimen tal dispersive effects linked to upwelling.