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Publication
Fate of discards from deep water crustacean trawl fishery off the south coast of Portugal
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Advisor(s)
Abstract(s)
Trawling for crustaceans takes place on the south coast of Portugal at depths between 200
and 800 m. Large amounts of discards are released back to sea, reaching the bottom in the general area
where trawling occurs. The objective of this work was to study the time taken for decomposition of the
discards, to identify the most important scavenging species involved, and to evaluate the impact on the
species targeted by the fishery. We conducted a series of 22 trials, using traps baited with samples of
the discards. The time of immersion varied between 1 and 40 h. The amount of tissue removed from the
discards was evaluated on a qualitative scale of 1–3, and quantitatively. The species caught in the traps
were identified. Considerable consumption of the bait had occurred after 5 h of immersion. After 24 h
of immersion only fish bones were left; past 40 h, consumption was complete. The conger eel (Conger
conger) was the most common fish species present in the traps. Two species, the amphipod Scopelocheirus
hopei and the isopod Natatolana (Cirolana) borealis, were identified as most important for the
recycling of organic matter in the system. The stomach contents of a sample of species caught in trawls
were analysed for the presence of small scavengers. Preliminary results show that S. hopei and N. (C.)
borealis are part of the diet of some of the target species of this fishery, such as the Norway lobster,
Nephrops norvegicus and the rose shrimp Parapenaeus longirostris.
Description
Keywords
Fate of discards Food subsidies Impact of trawling
Citation
Publisher
Royal Society of New Zealand