New Zealand Journal of Marine and Freshwater Research abstracts

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Fate of discards from deep water crustacean trawl fishery off the south coast of Portugal

MARGARIDA CASTRO
ARTUR ARAÚJO
PEDRO MONTEIRO

CCMAR Universidade do Algarve
8005-139 Faro, Portugal
email: mcastro@ualg.pt

Abstract  Abstract 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.

Keywords   fate of discards; food subsidies; impact of trawling

M04030; Online publication date 31 May 2005 Received 9 February 2004; accepted 26 April 2005
New Zealand Journal of Marine and Freshwater Research, 2005, Vol. 39: 437-446
0028-8330/05/3902-0437© The Royal Society of New Zealand 2005

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