Grey seals
Sable Island National Park Reserve
Sable Island National Park Reserve has the world's largest grey seal breeding colony.
Sable Island: The World's Largest Grey Seal Colony | Parks Canada
Transcript
Sable Island is home to the world’s largest breeding colony of grey seals.
Every winter, thousands of seals arrive to give birth to more than 80,000 pups.
The pups will nurse for 17 days and increase their body mass by almost 2kg every day.
Mature males stay close to the females, defending them from competing males.
Towards the end of lactation, the female will enter “oestrous” and mate.
She will then leave her weaned pup and head to sea.
At this point, the pups begin to lose their white coats.
They grow dense adult-like fur and remain on Sable Island for another three weeks.
Pups born early in the season are the first to leave the beach.
They will stay on the island for another three weeks, and with nothing to eat, they start slimming down.
Now they must teach themselves how to swim and hunt for food.
On this page
Morphology
Males may reach 2.3 metres in length and weigh up to 350 kg. Females can reach up to 2 metres in length and weigh up to 230 kg.
Behaviour
Several hundred thousand grey seals come to the island to mate and give birth each year in December and January. During the rest of the year, seals use the island to shed and regrow new skin and fur (moult) and to rest.
Breeding and pup stages
Breeding season occurs in December and January, during some of the coldest months of the year. Sable Island accounts for about 85% of the total grey seal pups born in Canada.
Newborn
Pups are born with white fur called lanugo. The newborn pups rely solely on their mother’s milk for their first 16 days, and during this time, they triple their birth weight.
Weaners
By the end of their first 16 days, the young ones have lost their white coat exposing a spotted juvenile coat. They are now called weaners. The mother grey seals return to the sea and the weaners are left to fend for themselves.
Weaners are seen all over Sable Island in the following months. They spend a large portion of their time sleeping. At times, they dig burrows for shelter and warmth while their fat converts to muscle.
After a month on the island, the weaners enter the water to feed for the first time. These juveniles are often spotted on the island all year long.
Diet
Grey seals consume a variety of fish species and invertebrates, and feed throughout the offshore banks.
Foraging
Sable Island’s male and female grey seals forage in different areas prior to the breeding season. Male grey seals forage closer to the mainland, in the western half of the Scotian Shelf. Females prefer to forage further out in the mid-shelf regions of the eastern shelf. This reduces competition for food between the two sexes.
Grey seals and horses
There is no direct competition for resources between horses and grey seals on Sable Island.
Grey seals bring large amounts of marine nutrients on land through their feces and urine. This promotes vegetation growth on the island. As horses on the island are dependent on vegetation for food, they benefit indirectly from the presence of seals.
Increased grey seal numbers may help explain the increase in horse population over the same period.
Population
Grey seals are found in the Gulf of St. Lawrence and on the Scotian Shelf (including the Bay of Fundy and the north-eastern United States). The breeding colony of grey seals found on Sable Island is of the same genetic population as those found elsewhere in Canada and the United States.
Population size
Grey seals and harbour seals have lived on Sable Island for hundreds of years.
In the 1950s, grey seals were rare in Canada and nonexistent in the north-eastern United States.
Population growth
Their numbers have greatly increased on the island in the last 60+ years. In the early 1960s, one hundred pups were observed on Sable Island, and in 2015 approximately 80,000 pups were observed!
The portion of Sable Island used by the grey seals has also increased. In the 1970s, most pups were born in a small area on the north beach at the eastern end of the island. More recently, grey seal pups are born all over the island, including inland. The only exception is that seals avoid the inland heath vegetation community.
The population growth has recently begun to show signs of slowing down. One explanation is the increased competition for resources, such as food and space.
Human interaction
Hunting
In the past, grey seals were harvested for fur, fresh meat, and other seal products on Sable Island.
Text version of the document
Sable Island May 28, 1819
Received from Edward Hodgson, on board the Schooner Two Brothers in good order and well conditioned, nine casks of Seal Oil, four casks of Black fish oil, and four barrels of Seal Skins, which I promise to Deliver to Michael Wallace, Halifax. Dangers of the Sea excepted.
Witness my Hand, Joseph Darby
Protection
Since the passing of the Marine Mammal Protection Act, grey seals have been protected throughout their range.
Research methods
Grey seals have been extensively studied at Sable Island National Park Reserve, with important discoveries made in several fields of biology. Research methods include indirect observation, seal cameras, and satellite tagging.
Indirect observation
Seals are free-ranging marine mammals that feed underwater, which means there are very limited opportunities to observe directly what they eat. Most research on their diet is done through indirect observations.
Researchers examine:
- hard bits present in their feces (such as squid beaks and fish ear bones)
- undigested stomach content
- lipids present in their blubber
- isotope ratios
- DNA present in feces
Seal cameras
Recently, scientists fitted cameras on Sable Island grey seals to observe what and how they forage. Early results suggest that grey seals eat a variety of fish species and invertebrates, including sand lance in particular.
Satellite tagging
In June, grey seals moult on Sable Island. Scientists use this opportunity to attach scientific monitoring equipment to the seals. The equipment is glued onto their fur. The devices are retrieved from the seals when they return to Sable Island to breed.
The monitoring equipment captures useful information like:
- seal diving depth and location
- physical and biological conditions of the deep ocean: water temperature, pressure, light intensity, and depth
- the presence of other tagged marine animals nearby
The information captured by the equipment allows scientists to study:
- seal movement and diving behaviour
- the physical and biological conditions in the deep ocean
- seal interactions with other animals and to identify ocean hotspots
More information
FREEDMAN, B., LUCAS, Z. et S. BLANEY. 2016. Marine Mammals. Dans Freedman, B. (éd.) 2016. Sable Island: the Ecology and Biodiversity of Sable Island. Fitzhenry and Whiteside, Markham, Ont.
BOWEN, W. D. et HARRISON, G. Seasonal and interannual variability in grey seal diets on Sable Island, eastern Scotian Shelf. NAMMCO Sci. Publ. 6, 123, 2007.
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