Integration of fishery-dependent data sources in support of octopus spatial management

Abstract

Octopus vulgaris is the most important target species in Portuguese fisheries in terms of economic value, when all official and non-declared landings are considered. Around 10% of the landings in national waters come from the trawl fleet, which is both the least selective and the best documented métier in the fishery, allowing the simultaneous assessment of distribution and population structure. This study represents a first attempt to integrate different sources of information obtained at commercial trip-level, with the objective of providing a perspective of octopus population structure and relative distribution, together with information on the exploitation pattern in 2003. High-quality resolution of sequential geo-referenced data were obtained from the Portuguese Vessel Monitoring System for the fishing trips targeting octopus. Intensive fishing activity was observed inshore of two regions, one to the north of Peniche (from Cape Carvoeiro to Portuguese border) and the other between Cape St. Vicente (Sagres) and Cape St. Maria (Faro) in the South coast. Fishing trips undertaken between 39.5 and 42°N were used to provide information on volume and size distribution of landings. These show that smaller individuals (=<12cm ML) are mainly concentrated between 40.5 and 41.5°N, whereas larger individuals (>12cm ML) concentrate south of 41.5 and north of 40.5°N.