Science Advisory Report  2012/054

Assessment of the impact of northern shrimp trawling on benthic habitats communities in the Estuary and northern Gulf of St. Lawrence

Summary

• The shrimp trawl used until now in the Estuary and Gulf of St. Lawrence is designed to maintain contact with the seafloor throughout a tow. Dragging the foot gear and doors along the seafloor disrupts the substrate, affecting benthic communities and habitats.
• The footprint of shrimp trawling was analyzed by reviewing the distribution of the cumulative fishing effort since 1982. Shrimp fishing generally takes place at water depths of 200 to 300 m in the Esquiman and Anticosti channels as well as along the two slopes of the Laurentian Channel as far as in the Estuary. The traditional fishing grounds are located in areas where surface sediments are fine and consolidated and where natural disturbances have minimal impact.
• Coral and sponge fields constitute vulnerable marine ecosystems that are sensitive to bottom trawling due to the sessile nature and low growth rate of these organisms. In the Gulf of St. Lawrence, significant concentrations of sea pens (soft corals) are observed in deep water in the Laurentian Channel, while sponges are distributed in aggregations throughout the area. Benthic communities may also constitute fragile ecosystems in that bottom trawling can reduce their diversity and modify their structure. The great majority of habitats suitable for the establishment of highly diverse benthic communities are found in coastal areas.
• The cumulative impact of shrimp trawling has likely been low on sea pen fields and highly diverse benthic communities since the depths targeted for fishing (200 – 300 m) are not optimal depths for the establishment of sea pen fields (>300 m) or highly diverse benthic communities (<200 m).
• Because sponge aggregations are found in a large range of depths, regular fishing activity may have affected their distribution. Moreover, important concentrations of sponges are observed in areas that were intensively fished in the 1980s but where little fishing activity has since been documented. Therefore, some recovery potential seems to be possible after a period of intensive trawling.
• The likelihood that shrimp fishing activities cause harm to vulnerable or fragile marine ecosystems is low to moderate. High concentrations of sea pens and sponges and habitats suitable for the establishment of highly diverse benthic communities are found on the periphery of traditional fishing grounds. The overlap between trawling activities and these vulnerable or fragile habitats could occur occasionally, as has been the case in the past.

This Science Advisory Report is from the May 17, 2012 Assessment of the impact of northern shrimp trawling on habitat and benthic communities in the Estuary and northern Gulf of St. Lawrence. Additional publications from this process will be posted as they become available on the Fisheries and Oceans Canada Science Advisory Schedule.

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