Science Advisory Report  2012/066

Importance of bycatch in the northern shrimp fishery in the Estuary and northern Gulf of St. Lawrence

Summary

• The shrimp fishery is carried out using small-meshed trawls that catch and retain several fish and marine invertebrate species. Although large fish are released from trawls due to the mandatory use of a separator grate since 1993, catches still contain a certain number of small specimens.
• Bycatches in the shrimp fishery were estimated using at-sea observer data for the 2000–2011 period (14 185 fishing tows). Catches noted by observers were weighted by total fishing effort in order to extrapolate the results to the entire shrimp fleet.
• Bycatches represent between 1.0 and 2.3% (in weight) of Northern shrimp catches for the entire period. Bycatches noted by observers were grouped under 97 taxa. A total of 16 of these were present in at least 10% of the tows whereas 59 were observed in less than 1% of the tows.
• The 10 most common species are Greenland Halibut, capelin, redfishes, Atlantic herring, American plaice, witch flounder, barracudina, thorny skate, Atlantic hagfish and marlin-spike. The 10 species with the largest bycatches (in weight) are capelin, Greenland Halibut, Atlantic herring, redfishes, American plaice, white shrimp, witch flounder, Atlantic cod, thorny skate, and barracudina.
• Bycatches of the most common groundfish species were compared with the results of the research survey in the Estuary and the northern Gulf of St. Lawrence for the same size ranges. Bycatches represent less than 1% in number and weight of the survey abundance and biomass estimates for each species.
• Catches of pelagic fish and invertebrates cannot be compared to the survey results. For the species that are harvested, there are much fewer bycatches than commercial landings. Bycatches of the other species that are not harvested totaled only a few tons over 12 years.
• Bycatches of vulnerable species (found in less than 0.25% of the fishing tows) and species at risk (found in 0.4% of the tows) are considered marginal compared to northern Gulf populations because they range from a few specimens to a few hundred kilograms per year.
• Although bycatches in the shrimp fishery are frequent and diversified, they remain low and should not have had an impact on Estuary and northern Gulf populations for the 2000–2011 period. Bycatches contribute to increasing mortality, but this increase is marginal in relation to the normal mortality rate for these populations.

This Science Advisory Report is from the Regional Science Advisory Meeting of October 23, 2012 on the Importance of Bycatch in the Northern Shrimp Fishery 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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