Abstract
As part of two research projects for analysing bycatch and discards, we quantified catch composition, catch rates, bycatch and discards in two important commercial bottom trawl fisheries (crustacean and fish trawls) off the southern coast of Portugal (Algarve). Stratified sampling by onboard observers took place from February 1999 to March 2001 and data were collected from 165 tows during 52 fishing trips. Commercial target species included crustaceans: blue and red shrimp ( Aristeus antennatus ), deep-water rose shrimp ( Parapenaeus longirostris ), Norway lobster ( Nephrops norvegicus ); and fishes: seabreams ( Diplodus spp. and Pagellus spp.), horse mackerels ( Trachurus spp.) and European hake ( Merluccius merluccius ). The trawl fisheries are characterised by considerable amounts of bycatch: 59.5% and 80.4% of the overall total catch for crustacean and fish trawlers respectively. A total of 255 species were identified, which belonged to 15 classes of organisms (137 vertebrates, 112 invertebrates and 6 algae). Crustacean trawlers had higher bycatch biodiversity. Bony fish (45.6% and 37.8%) followed by crustaceans (14.6% and 11.5%) were the dominant bycatch components of both crustacean and fish trawlers respectively. The influence of a number of factors (e.g. depth, fishing gear, tow duration and season) on bycatch and discards is discussed.
Highlights
Concern about bycatch in commercial and recreational fisheries can be found in the scientific literature from the mid-1970s, it became the most critical fisheries issue in the 1990s (e.g. Alverson et al, 1994; Kennelly, 1995; Alverson and Hughes, 1996; Hall et al, 2000)
Bottom trawling off the southern coast of Portugal generates significant amounts of bycatch, with the great majority
Part of the total bycatch includes non-target species of high commercial value, but a considerable portion consists of non-marketable target species, represented by undersized or poor quality specimens, and bycatch species with low or no commercial value that are discarded at sea in relatively similar proportions in both trawl types (Monteiro et al, 2001)
Summary
Concern about bycatch in commercial and recreational fisheries can be found in the scientific literature from the mid-1970s, it became the most critical fisheries issue in the 1990s (e.g. Alverson et al, 1994; Kennelly, 1995; Alverson and Hughes, 1996; Hall et al, 2000). Concern about bycatch in commercial and recreational fisheries can be found in the scientific literature from the mid-1970s, it became the most critical fisheries issue in the 1990s Given the overfished state of many of the worlds most important stocks (Pauly et al, 2002), there has been great in-. The worldwide interest has given rise to a significant number of research papers, reviews and conferences Saila, 1983; Alverson and Hughes, 1996; FAO, 1996; Hall, 1996, 1998; Zann, 2000; Sánchez et al, 2004; and many others). There is growing international concern for the conservation of bycatch species (Nakano et al, 1997). Alverson et al (1994) estimated an annual shrimp trawl bycatch of around
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