RESPONSES OF BENTHIC SCAVENGERS TO FISHING DISTURBANCE BY TOWED GEARSIN DIFFERENT HABITATS

The aggregation and feeding behaviour of invertebrate scavengers in ar eas disturbed by trawling was investigated at three different localiti es. At each site a fishing disturbance was created using a commercial 4 m beam trawl and scavenger density was quantified using a light beam trawl. At one site two diver surveys were also carried out; along a l ine fished with a scallop dredge or a beam trawl on two separate occas ions. For all experiments the fished and adjacent unfished control are as were sampled before, and at intervals after, the initial fishing di sturbance. Sampling with the light beam trawl revealed that hermit cra bs Pagurus bernhardus moved into areas which had been fished with a 4 m beam trawl at an experimental site near Anglesey. The density of the se hermit crabs increased significantly in the fished area after fishi ng had taken place, but no change in density occurred in the adjacent control (unfished) area. At two other sites (Red Wharf Bay, Anglesey a nd a site offshore from Walney Island) there were no detectable increa ses in scavenger numbers in the fished areas. Furthermore, at the site near Walney Island, numbers of hermit crabs P. bernhardus, swimming c rabs Liocarcinus depurator and starfish Asterias rubens actually decre ased after fishing. Thus the responses of scavengers to towed fishing gears varied considerably between different communities. At Red Wharf Bay, divers observed similar responses of scavengers to both beam traw l and scallop dredge disturbance. Four predatory species were observed feeding in the fished area; starfish A. rubens, hermit crabs P. bernh ardus, brittlestars Ophiura ophiura and whelks Buccinum undatum. These predators fed on damaged bivalves, echinoderms, crustaceans, whelks a nd polychaetes. The proportion of starfish feeding in the fished area was significantly higher after fishing had taken place. Demersal fishi ng activities provide food for scavengers in the form of damaged anima ls which are left in the tracks of the trawl or dredge. The responses of scavengers to fishing disturbance are not always manifested as a la rge increase in their abundance. It is clear that the magnitude of res ponse varies between species and between habitat types. (C) 1998 Elsev ier Science B.V.