1999 UMBSM/ IUEM/ ICRAM/ MLA Clyde Sea Toothed Dredge Impact Survey - Grab and Suction Sampling

Basic Metadata

DOI Maintainer:
Megan Mardle

Creator:
(University Marine Biological Station - Millport (UMBSM))

Publisher:
The Archive for Marine Species and Habitats Data (DASSH)

Year of Publication:
2023

Resource Type:
Dataset

Abstract:
1999 University Marine Biological Station, Millport, Marine observatory of the European University Institute of the Sea, ICRAM, Chioggia, Fisheries Research Services, Aberdeen Marine Laboratory Clyde Sea Toothed Dredge Survey An 18-month REEFS research project was undertaken to investigate the three main types of toothed dredge gear used for scallop (Pecten, Aequipecten spp.) fishing in Europe. Field investigations were carried out to assess the ecological impact of scallop dredging and experimental fishing studies were performed. The three scallop grounds which were investigated during the study were: Northern Adriatic (Italy); the Bay of Brest (North-Western France); and the Clyde Sea area (West coast of Scotland), which were paired sites. The study compared the effects of different types of toothed dredges on scallop grounds. Rapido trawls were used on the sandy bottom encountered in the Adriatic scallop fishing grounds. Brenton dredges were used in the French scallop grounds and Scottish grounds used the Newhaven trawl. Both scallop grounds were maerl based. The lighter weight rapido trawl penetrates surface sediment to 2cm to dislodge scallops and flat fish in the surface of the sea bed. Both the Brenton and Newhaven trawls penetrated the sediment surface down to 10cm. They are designed to be heavier to cope with more difficult fishing grounds. Toothed dredging field manipulation experiments identified the major ecological impacts of scallop fishing. The study established that toothed dredging had an impact on the sediment surface physical features, re-suspended silt fractions and disrupted sessile epifauna and habitat characterization. Dredging tracks were littered with dead or damaged organisms which attracted scavengers. Dredging tracks can be visible for a period of months to years. Areas with highly mobile sediment characterization were able to erase the effects of dredging faster than areas of sheltered mud or maerl. Experimental impact assessments were performed to determine the effects of dredging on surface living and sessile organisms. The experiments were conducted on sites in the Adriatic, France, and Scotland where commercial fishing was not possible. Bottom samples (up to 60cm below the sea bed) were taken via suction-lift techniques. Water lifts were used in the Adriatic site while air lifts were used in the French and Scottish sites. Sampling was also conducted using grabs. The investigations revealed that organisms living in the surface layer of the sea bed are disturbed by the process of dredging, however organisms are small enough to deter damage and survive. Deep burrowing organisms, large and long-lived species, are protected from toothed dredges (as adults). Large, sessile epifauna are the organisms which suffer the most impact of dredging and form the bulk of by-catch. Damaged organisms and discards of dredging are exploited by scavenging organisms. Toothed dredges are renowned to be the most environmentally damaging of the fishing gear which is towed in European waters. The project has established that toothed dredges affect the same sea bed area differently and therefore impacts the ecology of the substrata differently.

Description:
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