ABSTRACT. Four 100 m lengths of both monofilament gill nets and trammel nets were deployed at depths between 15 and 18 m off the coast of the Algarve (south of Portugal) between April 1995 and June 1996. The nets were set on a natural rocky bottom with one end cut loose to simulate lost nets.Changes in net structure (net height, effective fishing area, movement, colonisation, wear and tear) and their catches (species, sizes, numbers, and biomass) were monitored by divers. Similar patterns were observed in all the nets, with a sharp decrease in net height and effective fishmg area, and an increase in visibility within the first few weeks. Net movement was negligible except in the case of interference from other fishing gears. Catch rates were initially comparable to normally fished gd.l nets and trammel nets in this area, but decreased steadily over time. No sea birds, reptiles or mammals were caught in any of the 8 nets. Catches were dominated by fish (89% by number, at least 27 species), in particular by sea breams (Sparidae) and wrasscs (Labridae). Under the conditions experienced throughout the study the fishlng hfetime of a 'lost' net is between 15 and 20 wk. Based on an exponential model, we estimated that 100 m lengths of gill net and trammel net will catch 314 and 221 fish respectively over a 17 wk period.However, we consider this to be an underestimate due to high rates of predation and scavenging by octopuses, cuttlefish, moray eels, conger eels, and other fish such as the wrasse Coris julis. When the nets were surveyed in the following spring. 8 to 11 mo after being deployed, they were found to be completely destroyed or heavily colonised by algae and had become incorporated into the reef.KEY WORDS: Lost gear. Ghost fishing. Gill n e t . Trammel n e t . Catches. Incidental mortality INTRODUCTIONThe impact of lost fishing gear on the environment has aroused considerable concern in recent years (Laist 1995). Of particular concern is the danger posed to rare and endangered species of marine mammals, sea birds and turtles (Degange & Newby 1980, Henderson 1984, Millner 1985, Perrin et al. 1994. It has been estimated that millions of sea birds and thousands of turtles and marine mammals may die each year when entangled or trapped in lost gear (Colema et al. 1983). In commercial fisheries, incidental mortality due to gear over which the fisherman has lost control, may be highly significant (Chopin et al. 1995). 'Ghost fishing' can be defined as the capacity of a fishing gear to continue to fish after it has been lost and the fisherman has lost control. For example, Breen (1987) estimated that ghost fishing traps caught a n amount equivalent to 7 % in weight of the reported commercial catch of Dungeness crab. Similarly, lost fish traps were estimated to catch a quantity equivalent to 3-13.5% of the total Kuwait landings (Mathews et al. 1987), and the decline in Gulf of St. Lawrence Queen crab has been partially attributed to mortality associated with lost crab traps (Blois 1992).In addition to being a source...

Weight and length descriptive statistics are reported for 73 fish species discarded in the commercial fisheries from the south coast of Portugal. Parameters of the weight-length relationship were estimated for 57 of these species. These are the first weight-length parameters reported for 20 of these species. For an additional 16 species for which no weight-length parameters have been reported, the parameter a was estimated by setting b ¼ 3.0. Samples were used from five gear types: crustacean trawler, fish trawler, pelagic purse seine, demersal purse seine and trammel net. Samples were obtained from depths ranging from <30 m to >500 m and included pelagic and demersal species.

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Discards from five of the most important fisheries (crustacean trawling, fish trawling, demersal purse seining, pelagic purse seining and trammel netting) in southern Portugal were studied and compared. A total of 236 species of all taxa were discarded, with fish and cephalopods accounting for more than 90% of the discarded biomass, except trammel nets (81%). Although there was some overlapping of species, multivariate analysis using cluster analysis for classification and multidimensional scaling (MDS) for ordination, showed that there were significant differences between the five gears in terms of species composition and biomasses discarded, with the least similarity between crustacean trawling and all other fishing operations. The differences between fisheries were probably as a result of a combination of gear selectivity and depth fished. The results suggest that discarding practices are likely to have different, yet significant impacts on the marine ecosystem, warranting further studies on the fate of discards, the factors influencing discarding and mitigation.

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