BIOLOGY AND FISHERY OF OCTOPUS-VULGARIS CUVIER, 1797, CAUGHT BY TRAWLERS IN MALLORCA (BALEARIC SEA, WESTERN MEDITERRANEAN)

Some aspects of the biology and fishery of Octopus vulgaris caught by trawlers in the Balearic Sea (Western Mediterranean) are studied. The analysis of the size-frequency distribution followed the growth of spe cimens from January (6-7 cm ML) to August (11-12 cm ML). The sex ratio was estimated for each season and it was not significantly different from 1 : 1 in any of them. The stomach contents revealed that the octo pus fed predominantly on crustaceans and fishes. Another octopus speci es, Eledone moschata, is present in this fishery but its catches were clearly lower than those of O. vulgaris. The analysis of the importanc e of these two species in relation to the rest of the commercial catch showed that octopuses represent between 20-40% of the total catch for trawlers. The highest catch rates (kg/h) were obtained in spring and at the beginning of summer. Time-series analysis of monthly catches fr om January 1981 to August 1996 showed two main oscillations. The lower one, with a periodicity of 12 months, reflects the annual biological cycle of the species; on the other hand, the higher one has a periodic ity of 92 months, the time series available being too short to confirm the significance of this period. (C) 1998 Elsevier Science B.V. All r ights reserved.