Science Advisory Report 2009/067
Science Advice on Harvesting of Northwest Atlantic Grey Seals (Halichoerus grypus) on Hay Island
- Grey seals form a single genetic population that is divided into three groups based on the location of breeding sites. Most pups (81%) are born on Sable Island, 15% are born in the Gulf and 4% are born along the Eastern Shore of Nova Scotia. This distribution has changed over time, with a decline in the fraction of the population born on the ice compared to that born on small islands, and an increase in the proportion of animals born on the Eastern Shore, compared to the Gulf.
- Using aerial surveys, total production of Northwest Atlantic grey seals in 2007 was 67,500 (SE=1,400). This includes 54,500 (SE=1,300) pups born on Sable Island, 3,000 (SE=40) along the eastern shore of Nova Scotia (mainly Hay Island), and 9,900 (SE=600) in the Gulf of St. Lawrence.
- To determine the date of weaning and departure of pups from Hay Island, data on changes in the proportion of pup in age-related stages and stage durations were used to model the distributuion of births and weaning. Data on proportions in different stages were collected from Hay Island in 2000, 2007, and 2008.
- Pupping on Hay Island begins in late December, and 50% of births occurred on average by 10 January. Given that lactation lasts for 19 days, about 90% of pups will be weaned by 11-15 February. Fully moulted pups (beaters) will be encountered on the island beginning in February, assuming a mean age of 25 days, Beaters begin entering the water at about 8 February and almost all animals will have left by 4 March.
- A conceptual model provides guidance on when harvesting might occur. If harvesting activities begin too soon the pupping season may be disrupted, Waiting too long will result in animals dispersing from the island. Harvesting after 10 February would encounter few adults still nursing, would have a large proportion of beaters present and very few beaters are likely to have dispersed by that time.
- Date modified: