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

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.

1999年克莱德海齿式扒网调查由米尔波特大学海洋生物站、欧洲海洋大学研究所海洋观测站、ICRAM、基亚奥贾渔业研究服务处、阿伯丁海洋实验室联合实施。本项目为为期18个月的REEFS研究计划，旨在调研欧洲用于扇贝（*Pecten*、*Aequipecten*属）捕捞的三类主流齿式扒网作业装备。研究通过野外调查评估扇贝扒网作业的生态影响，并开展了试验性捕捞研究。
本次调研覆盖三处配对采样渔场：意大利北亚得里亚海、法国西北部布雷斯特湾，以及苏格兰西海岸克莱德海海域。研究对比了不同类型齿式扒网对扇贝渔场的影响：亚得里亚海扇贝渔场以沙质底质为主，作业采用Rapido拖网；法国与苏格兰的扇贝渔场均以藻形珊瑚（maerl）底质为主，前者使用Brenton扒网，后者则采用Newhaven拖网。
重量更轻的Rapido拖网可穿透表层沉积物至2厘米深度，以驱离海床表层的扇贝与比目鱼；Brenton与Newhaven拖网的穿透深度可达10厘米，这类装备设计重量更大，以适配作业条件更严苛的渔场。
齿式扒网野外操控试验明确了扇贝捕捞作业的主要生态影响：研究证实，齿式扒网作业会改变沉积物表层物理特征、再悬浮粉砂组分，并破坏固着表栖生物与栖息地表征。作业拖曳轨迹上遍布死亡或受损的生物，进而吸引食腐生物聚集；拖曳轨迹可在数月至数年的时间内保持可见。沉积物活动性较强的区域，其受扒网作业影响的痕迹清除速度快于受庇护的泥质或藻形珊瑚底质区域。
本研究开展了试验性影响评估，以确定扒网作业对表层栖息生物与固着生物的影响。试验在亚得里亚海、法国及苏格兰的非商业捕捞样地中进行，采用抽吸提升技术采集海床以下至多60厘米的底质样本：亚得里亚海样地使用水提装置，法国与苏格兰样地则使用气提装置；此外还采用采泥器开展补充采样。
调查结果显示，海床表层栖息的生物会受到扒网作业的干扰，但体型足够小的生物可规避损伤并存活；深穴居生物、大型长寿物种（成体）则可免受齿式扒网的影响。大型固着表栖生物受扒网作业影响最为严重，且构成副渔获物的主体。受损生物与捕捞丢弃物会被食腐生物利用。
齿式扒网被公认为欧洲海域拖曳类捕捞装备中对环境破坏最严重的一类。本项目证实，齿式扒网对不同海床区域的影响存在差异，因此对底栖生境生态系统的影响也各不相同。