Effects of experimental otter trawling on surficial sediment properties ofa sandy-bottom ecosystem on the Grand Banks of Newfoundland

We conducted a 3-year experiment on the effects of otter trawling on benthi c habitat and communities on a sandy-bottom ecosystem of the Grand Banks of Newfoundland that has supported commercial fisheries. Each year; three 13- km-long corridors were trawled 12 times with an Engel 145 otter trawl, crea ting a disturbance zone 120-250 m wide. Using a variety of oceanographic in struments, measurements were made before and after trawling to document eff ects. Trawling had no detectable effect on sediment grain size. Tracks made by trawl doors were readily visible on the sea floor immediately after tra wling and 10 weeks later; in some cases they were still faintly visible aft er I year Acoustic data indicated that trawling increased the topographic r elief or roughness of surficial sediments and changed small-scale biogenic sediment structures down to depths of 4.5 cm. Video observations in trawled corridors revealed that organisms and shells tended to be organized into l inear features parallel to the corridor axis. They also demonstrated that t rawling reduces both surficial biogenic sediment structure and the abundanc e of flocculated organic matter; untrawled sediments had a hummocky, mottle d appearance whereas trawled sediments were smoother and cleaner. These cha nges combined to give the trawled corridors a lighter appearance in color. It appears that the physical effects of otter trawling observed in this exp eriment are moderate and that recovery occurs in about a year The biologica l effects of this experimental trawling have yet to be examined.