Researching the impacts of climate change on marine mammals
Learn how climate change is impacting animals in the Arctic, Hudson Bay, Gulf of St. Lawrence and Northwest Atlantic.
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Arctic sea ice
We expect the Arctic to show the fastest changes from global warming.
In Arctic ecosystems, sea ice helps regulate ocean and atmosphere exchanges of:
- gas
- heat
- water
Sea ice also:
- restrains access to some areas for other marine mammal species, such as beluga whales
- serves as a habitat for some marine mammal species for haul-out (leaving the water for reproduction or rest), including walrus and ringed seals
Over the last 4 decades, we've seen a decline in sea ice:
- extent
- duration
- thickness
Climate change scenarios predict that this current trend will continue.
Hudson Bay animals
We predict the rate and intensity of climate change to be greatest at the southern and northern distribution limits of ice-obligate and seasonal migrant species, respectively. Studies aiming to anticipate the consequences of climate change on marine mammals and Arctic ecosystems have focused on Hudson Bay, which has both conditions.
Hudson Bay is a large (around 1.2 million kilometres squared), seasonally ice-covered inland sea. It's inhabited by:
- seasonally ice-associated migrant species
- a variety of Arctic or ice-obligate resident marine mammal species
Top predators in the Hudson Bay include Inuit hunters and polar bears.
Polar bears
Hudson Bay represents polar bears southern range limit. This species uses ice from freeze-up to breakup to:
- forage, primarily on ringed seals
- fast throughout the summer on land
The ice-covered period is important for helping polar bears get the energy they need to survive the summer. However, climate change is decreasing feeding opportunities due to less prey supply and shortened foraging periods.
Ringed seals
Ringed seals depend on fast-ice for their reproduction. They give birth and nurse their pups in subnivean (under the snow) caves for about 6 weeks.
Reductions in fast-ice cover and duration will likely result in:
- a reduced lactation period
- increased predation on young
- higher pup mortality
- a decline in ringed seal abundance
Harbour seals
Although considered as a northern temperate species, small numbers of harbour seals are found in Hudson Bay.
This species prefers ice-free waters. They give birth and nurse their young on land. The reduction in ice coverage and duration in Hudson Bay leads us to believe that harbour seal abundance could:
- increase in this area
- eventually replace ringed seals as a primary food source for polar bears
However, harbour seals prefer nearshore, shallow water areas. This limits the ability for population growth to high enough numbers to replace ringed seals in polar bear diets.
Moreover, ringed seals are more accessible prey for polar bears, as throughout lactation:
- pups remain relatively passive in their caves
- adults return to breathing holes in the ice
In contrast, harbour seal pups are highly aquatic from birth to weaning. Their use of ice-free waters makes them less predictable and vulnerable to predators.
Killer whales
Killer whales haven't always been present in Hudson Bay. There were some sightings from as early as 1900 in Hudson Strait. In the 1940s, the number started to increase. Killer whales are now regularly seen in Hudson Bay.
Unlike beluga and bowhead whales, killer whales have high profile dorsal fins. This makes it hard for them to move through heavy ice. Evidence suggests that sea ice in Hudson Strait acted as a choke (stopping) point, restricting killer whale access to Hudson Bay. With the decline in sea ice, the species population has now been able to expand.
As temperate waters shift to higher latitudes due to climate change, killer whales are expected to expand their range farther into Canadian Arctic waters. This may result in an ecological shift, with killer whales replacing polar bears as the top marine predator in some areas.
Killer whales in Hudson Bay feed on:
- seals
- whales, including:
- bowhead whales in the summer
- narwhals and belugas in the spring and fall
Inuit harvest polar bears for food and offset their expenses through the sale of the hide. Scientists expect that the replacement of polar bears by killer whales as top predators will result in complex ecosystem and social changes.
Harp seals in the Gulf of St. Lawrence and Northwest Atlantic
The most abundant marine mammal in the North Atlantic is the harp seal. They play a key role in the ecosystem.
Harp seals also represent social and economic interests, as they're harvested for commerce and subsistence in the Northwest Atlantic.
This species depends on pack-ice to:
- give birth
- nurse their young
- moult (shed their hair)
The nursing period lasts on average 12 days, after which the weaned animals continue to remain on the ice for several weeks.
For harp seals to successfully reproduce, the presence of pack-ice pans of sufficient size and thickness are required. They need it from whelping (mid-February) until young of the year have developed their swimming abilities and migrate northward to the Arctic.
Pack-ice presence and thickness has been decreasing in the North Atlantic and the Gulf of St. Lawrence over the last 40 years.
Climatic simulations predict a 70% decrease in ice duration in the Gulf of St. Lawrence by 2050. From 2009 to 2010, and from 2010 to 2011, ice conditions were the lowest in the Northwest Atlantic since the Canadian Ice Service began compiling daily ice charts in 1969.
Responses to ice conditions
The way in which harp seals responded to these extreme ice conditions provides insights into how this species may respond to future changes.
In March and April 2010, ice was absent from the Gulf of St. Lawrence at the time females usually give birth. No significant whelping was observed to occur in the Southern Gulf in this year. Instead, females moved to more suitable ice, outside of the Gulf, to an area referred to as the Front, off the southeast part of Labrador.
From 2010 to 2011, ice formed late in the Gulf and Northwest Atlantic, but the ice was thin. Pupping occurred in the normal areas, but broke up rapidly after most of the females had given birth. Mortality in March and April 2011 was considered very high.
Observations from these 2 years suggest that if ice is:
- destroyed, mortality could be high
- not present, females will attempt to move elsewhere in search of suitable ice
- suitable at the beginning of the pupping season, females will give birth in the traditional breeding areas
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