Preliminary results on the effect of otter trawling on hyperbenthic communities in Heraklion Bay (Eastern Mediterranean, Cretan Sea)

Although the benthopelagic fish species are a focus of commercial exploitation, relatively little attention has been paid to the small-sized invertebrates (0.5-20mm) living on or very close to the seabed, thus inhabiting the same biotope, known as well as “hyperbenthos”. Recently interest in this faunal group has increased, as many demersal fish and epibenthic crustaceans have been found to feed on hyperbenthic animals, for at least part of their lives. Otter trawls, the most common gear used for demersal fishing, result in significant disturbance of the sediment-water interface. Animals that are disturbed by the passage of a trawl may become more available to predators and scavengers. We have been unable to find any reports of studies of the impacts of towed fishing gears, including otter trawls, on hyperbenthos. We studied these effects on the Mediterranean continental shelf in Heraklion Bay (Cretan Sea), using a novel apparatus to simulate the contact of otter trawl groundrope with the sea bed. A modified three-level hyperbenthic sledge was used for collecting disturbed (groundrope present) and undisturbed (without groundrope) macrofaunal samples at a towing speed typical of the local commercial vessels. Observations were made in an area being actively fished, before and during the trawling season. The preliminary results reported here indicate that trawling causes significant changes in the structure of hyperbenthic communities.