Abstract
In an attempt to detect changes in the diet and the feeding intensity of demersal fish caused by fishery discarding, two hauls were carried out 22 h apart at a depth of 90 m in an area of the Cantabrian Sea closed to trawling. Before the second haul, dead fauna that were not common in the sampling area under natural conditions, such as Micromesistius poutassou and squat lobster (Munida spp.), which are both usually discarded by the fleet and mainly found in deeper water, were thrown overboard. A total of 319 stomach contents from 12 demersal fish species caught in both hauls were analysed. The percentage emptiness decreased in the second haul (32%) with respect to the first (43%), and at the same time the feeding intensity of scavenger species such as Trachinus draco, Pagellus acarne, Scyliorhinus canicula, Raja montagui and Leucoraja naevus increased. Discards of M. poutassou was actually found in the stomach of a typically planktophagous species, Pagellus bogaraveo. Observed changes in trophic structure of the species analysed as a response to discards are discussed.
Highlights
In the course of fishing operations, species of no economic value are often discarded
When such discarded material is on or near the surface, it can be consumed by birds (Furness et al, 1988; Hudson and Furness, 1988; Camphuysen et al, 1995), but the balance sinks through the water column, where it may be consumed by pelagic scavengers such as fish, sharks and cetaceans
The biomass indices from bottom trawl surveys carried out before and after the creation of the closed trawl area were used to determine the impact of this management measure
Summary
In the course of fishing operations, species of no economic value are often discarded. When such discarded material is on or near the surface, it can be consumed by birds (Furness et al, 1988; Hudson and Furness, 1988; Camphuysen et al, 1995), but the balance sinks through the water column, where it may be consumed by pelagic scavengers such as fish, sharks and cetaceans. Camphuysen et al (1995) and Garthe et al (1996) consider that 20% of discarded material (mainly gadoids and the contents of the body cavity) in the North Sea are consumed by birds, whereas the remaining 80% (e.g. echinoderms, molluscs) sink to the seabed. According to Wassenberg and Hill (1987; 1990), 35% of the discards in a Queensland shrimp fishery (mainly fish and cephalopods) is consumed on the surface and the other 65% (crustaceans, echinoderms) reaches the seabed. Predators and scavengers congregate in such areas disturbed by bottom trawl fishing gear, occasionally changing their dietary preference (Kaiser and Spencer, 1994, 1996; Ramsay et al, 1996, 1998; Kaiser and Ramsay, 1997; Kaiser et al, 1998)
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