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Fleet dynamics in multispecies trawlers: a study based on fisheries-dependent data
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Authors
Abstract(s)
Fishery-dependent data from the Portuguese coastal fish trawl fleet were integrated to
examine fleet segmentation and dynamics along a 13-year period, and estimate speciesdirected
effort and abundance. Six landing profiles (LPs) were based on the relative
importance of target and by-catch species, including horse mackerel (Trachurus
trachurus) and blue whiting (Micromesistius poutassou) almost exclusive LPs, three
others corresponding to trips targeting squids (Loligo spp.), horse mackerel and
octopuses, as the main species. LPs were assigned to trawlers, defining fleet
components with specific technical characteristics and fishing strategies. This showed
that large vessels target pelagics along the entire coastline, average-powered units fished
a diverse catch off the Central zone of the western coast, including horse mackerel and
cephalopods and a group of trawlers targeted cephalopods and benthic species off the
south coast.
Vessel Monitoring System (VMS) data, processed by GeoCrust 2.0, was used to
quantify effective fishing effort and define geographic patterns of fishing activity.
VMS-based species-specific effort from 2003 was integrated with landings to estimate
landings per unit effort (landings per day at sea and landings per hour trawled.
Integration of cephalopod size-classes data with VMS information enabled the
estimation of size-dependent effort and analysis of geographical patterns of population
structure.
A group of vessels with landing activity and VMS coverage of trips belonging to
distinct LP were selected to constitute a potential sample fleet for estimating speciesdirected
LPUE. Their representativeness in terms of effort and LPUE was examined by
comparing these results with those obtained for the entire fleet. This reduced fleet was
found to be a possible candidate for a sampling programme under the EU Data
collection Framework. Overall findings highlight the benefits of combining fisheriesdependent
data, to produce information relevant for integrated management, in
accordance with the Common Fisheries Policy and Marine Strategy Framework
Directive objectives.
Description
Tese de doutoramento, Ciências do Mar, da Terra e do Ambiente (Avaliação e Gestão de Recursos), Faculdade das Ciências do Mar e do Ambiente, Universidade do Algarve, 2013
Keywords
Pescas Gestão das pescas Recursos marítimos Frota pesqueira Pesca de arrasto