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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...

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The crustacean trawl fishery off the Algarve coast (southern Portugal) takes place on the lower continental shelf and upper continental slope at depths between 150 and 600 m. This is a multi-species fishery targeting the shrimps Parapenaeus longirostris and Aristeus antennatus and the Norway lobster Nephrops norvegicus, with the latter two species the most important in the landings. The fishery is characterised by significant by-catch and discarding of a large number of species. As part of a study on the fate of trawl fishery discards, this component of the study focused on the quantification of the by-catch and discards of crustacean trawlers. Sampling took place on board seven commercial trawlers from June 1998 to October 1999. Data was collected from 48 tows in 22 fishing trips. The observers collected all of the catch that was discarded by the crew during the sorting operation and samples were taken to the laboratory for identification, weighing and measuring. The quantities of target species were recorded along with the presence of retained by-catch. Commercially valuable species that were retained included Plesiopenaeus edwardsianus, Aristeomorpha foliacea, Plesionika sp., and the fishes Lophius piscatorius and Merluccius merluccius. However, most of the species had no or little commercial value and were almost always discarded to the sea (90%). A total of 91 species were identified, 47 vertebrates and 44 invertebrates corresponding to 65 families. The Teleostei (78% and 68%) were the dominant group, both in number and weight. The species Micromesistius poutassou (34%), Gadiculus argenteus (10%) and Hoplostethus mediterraneus (8%) were the most important in weight. Ten species represented more than 82% of all discards in weight. Gadiculus argenteus (29%), Hoplostethus mediterraneus (21%) and Nezumia sclerorhynchus (10%) accounted for 60% of all discards in numbers. Data on the landed species composition is also presented.