On the identity of Octopus vulgaris Cuvier, 1797 stocks in the Saharan Bank (Northwest Africa) and their spatio-temporal variations in abundance in relation to some environmental factors
Abstract:Using data from the Spanish octopus (Octopus vulgaris Cuvier, 1797) fishery occurring on the Saharan Bank (Northwest Africa between 21°N and 26°N), oscillations on the spatio-temporal abundance of the species are analyzed by means of a Geographic Information System (GIS) and by applying Generalized Additive Models (GAM) as exploratory tools. GIS analyses show two differenciated fishing grounds respectively located north and south of Dakhla (25°N). During the recruitment period of octopus, fishing activity tends to concentrate at both areas in relatively small high density spots from where it gradually extends to occupy almost the whole region at the end of the fishing season. The intermediate zone between these two major fishing grounds is rarely exploited at any time of the year. A GAM fitted to the data also reveals the existence of those two zones of high abundance of octopus in the Saharan Bank indicating that its intra-annual variability is mostly related to the latitude, the longitude (depth) and specially to the period of the year being maximum in October–November when sea surface temperature is highest. Nevertheless, major fluctuations in octopus abundance seem to occur at an inter-annual scale and some evidence suggests that they could be related to anomalies in the mean annual sea temperature in the region. Previous observations are reviewed and hypotheses are put forward suggesting possible relationships between spatio-temporal changes in octopus abundance and distribution and environmental factors.
Document Type: Research Article
Publication date: July 1, 2002
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