The impact of Rapido trawling for scallops, Pecten jacobaeus (L.), on the benthos of the Gulf of Venice

Rapido trawls are used to catch sole around the coast of Italy and to catch scallops in the northern Adriatic Sea but little is known about the enviro nmental impact of this gear. Benthic surveys of a commercial scallop ground using a towed underwater television (UWTV) sledge revealed an expansive ar ea of level, sandy sediment at 25 m characterized by high population densit ies of scallops (2.82 m(-2) Aequipecten opercularis but fewer Pecten jacoba eus) together with ophiuroids, sponges, and the bivalve Atrina fragilis. Ra pido trawls were filmed in action for the first time, providing information on the selectivity and efficiency of the gear together with its impact on the substratum and on the benthos. The trawls worked efficiently on smooth sand with ca. 44% catch rate for Pecten jacobaeus, of which 90% mere >7 cm in shell height. Most organisms in the path of the trawl passed under or th rough the net; on average by-catch species only formed 19% of total catch b y weight. Of the 78 taxa caught, lethal mechanical damage Varied from <10% in resilient taxa such as hermit crabs to >50% in soft-bodied organisms suc h as tunicates. A marked plot surveyed using towed UWTV before, then 1 and 15 h after fishing by Rapido trawl showed clear tracks of disturbed sedimen t along the trawl path where infaunal burrow openings had been erased. Abun dant, motile organisms such as Aequipecten showed no change in abundance al ong these tracks although scavengers such as Inachus aggregated to feed on damaged organisms. There were significant decreases in the abundance of slo w-moving/sessile benthos such as Pecten, Holothuria, and Atrina. Juvenile p ectinids were abundant on the shells of Atrina. The introduction of a schem e of areas closed to trawling would protect highly susceptible organisms su ch as Atrina and enhance the chances of scallop recruitment to adjacent are as of commercial exploitation. (C) 1999 International Council for the Explo ration of the Sea.