Science Advisory Report 2013/008

Stock Assessment of Northwest Atlantic grey seals (Halichoerus Grypus)

Summary

• Grey seals form a single genetic population that is divided into three groups for management purposes based on the location of breeding sites. Most pups (81%) are born on Sable Island, 15% are born in the Gulf of St. Lawrence and 4% are born along the coast of Nova Scotia. This distribution has changed over time, with a decline in the fraction of the population born in the Gulf.
• A population model incorporating estimates of reproductive rates up to 2011 was fitted to pup production estimates up to 2010 to describe the dynamics of the grey seal population in Atlantic Canada. Combining all three herds, the model estimated a total 2012 grey seal pup production in Atlantic Canada of 76,200 (95% CI=60,000-105,000) animals, with an associated total population of 331,000 (95% CI=263,000-458,000). Population size in all three management areas appears to be leveling off.
• The current estimate of population size is slightly lower than what was presented in 2010 due to differences between the types of models used in the assessment. The difference does not represent a change in abundance but rather a change in methods used to estimate abundance.
• Removals from the population during the last five years include animals taken in the commercial harvest, for scientific collections, nuisance seals (seals removed for damaging gear and catches), and incidental catches in commercial fisheries. Estimates of the number of seals killed as nuisance seals are incomplete. There is no data available on incidental catches, but the numbers are thought to be small.
• Projections from the population dynamics model were used to investigate the consequences of a range of harvest strategies. Harvests of 36,700 animals (97% Young of the Year) would maintain an 80% probability of staying above N70 and a 95% probability of staying above N30. Higher harvest levels would be possible, but with lower probabilities of remaining above N70 and N30.
• If the proportion of Young of the Year in the catch declines to 50%, then harvests of 19,900 animals (97% Young of the Year) would maintain an 80% probability of staying above N70 and a 95% probability of staying above N30. Higher harvest levels would reduce the probabilities of remaining above N70 and N30. 

This Science Advisory Report is from the October 29 to November 2, 2012 Annual meeting of the National Marine Mammal Peer Review Committee. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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