The impact of fish trawls on megabenthos (sponges) on the north-west shelf of Australia

摘要: Abstract We attempted to resolve widely different accounts of the impacts fish trawls on large attached seabed fauna. quantified catch and damage by sponges used a video camera in trawl net observe effects fishing gear sponges. The depth 30 min tows ranged from 25 358 m, with an average 78.3 m. Sponges were caught 85% (n=108). mean was 87.2 kg for half-an-hour ( S.D. =132.9 kg ) . largest single 797 kg. All catches more than 100 kg sponge waters shallower 100 m. On basis our observations, we divided into two types lump = broad base , branched narrow three height classes 500 mm). size composition seabed, as observed video, differed significantly catch: 80% 100% less 300 mm passed under net; 68% between 301 500 mm net. Fewer 3% intermediate-sized broken up they larger high impacted most: only 30% 60% Of 70% that net, at least 20% pieces. either torn off footrope (20%) or smashed rolled (20%). Over 90% another major megabenthic group, gorgonians, Overall, removed about 14% gorgonians. impact commercial trawling megabenthos is estimated year. Our results provide mechanism main otter trawling: (1) reduction especially understanding sponges; (2) changes species trawled areas.