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 ) populations and environmental conditions off the Arguin Bank (Mauritania) in the main nursery ground was investigated between 1990 and 1996. Three environmental indices (coastal upwelling intensity, coastal retention and wind-induced turbulence indices) are derived from satellite infrared imagery (METEOSAT) and from the COADS (Comprehensive Ocean–Atmosphere Data Set) data to quantify the coastal retention process and productivity, both believed to be important factors for recruitment success. The octopus recruitment index as well as environmental indices fluctuate annually and seasonally. Linear regression and generalized additive models (GAM) are used to relate recruitment indices and the environmental conditions prevailing during the early-life planktonic stage, known to be the main critical period of the octopus life cycle. Coastal retention especially appears to be a key factor for recruitment success. Owing to seasonal variations in enrichment and mixing processes, larvae benefit from retention in the spring but are negatively affected by a breakdown in retention in the autumn. Increasing upwelling intensity is beneficial for octopus recruitment, as the Arguin Bank limits the detrimental dispersive effects linked to upwelling.