The study from Duke University in North Carolina warns climate change and disappearing sea ice off Canada's east coast could prove to be a more dire challenge for the animals going forward, with entire year-classes of seal pups dying as a result of diminished breeding spaces.
The study said a look at the Gulf of St. Lawrence shows that population fluctuation — for better or worse — is dependent on a climatic phenomenon known as the North Atlantic Oscillation (NAO), which controls the strength and path of westerly winds and affects the volume of sea ice in the region. The Gulf region serves as a breeding zone for many harp seals.
"When you account for the good-ice years vs. bad-ice years . . . the result is a long-term decline in sea ice . . . of about six per cent per decade," said David Johnston, a research scientist at the Duke University Marine Lab. "You'll still have good-ice years and you'll have bad-ice years, but it seems over time, the number of bad ice years overwhelms the number of good ice years.
"Harp seals aren't endangered right now, so we're not worried they're going to disappear off the face of the earth . . . but we're all concerned about what's happening with climate change, so it's important to try and anticipate what's in store for these animals over time."
Some years the NAO results in less sea ice, thus reducing population growth, while other years — such as the period between 1973 and 2000 — resulted in a period of "steady recovery."
Johnston said a major question remains surrounding the breeding habits of harp seals and how willing they would be to seek refuge elsewhere to breed should ice levels in more southern regions continue to decline.
Longtime sealer Jack Troake, of Twillingate, N.L., has taken part in the commercial seal hunt since 1952 and has witnessed his share of ice conditions and seal populations. He admits there are issues affecting harp seals of Canada's east coast, but isn't convinced it's exclusive to sea ice.
"It's not that I don't give a rat's ass (about ice levels)," Troake said Wednesday. "There is something drastically wrong with the harp seals, I can tell you that, but I don't think it's because of ice conditions. These animals are pretty smart and cagey and they'll go off until they find the proper ice."
Johnston, however, said it remains unclear how dedicated the seals are to breeding in specific areas, even if the conditions don't always allow for population growth.
"The places they breed, they come back to relatively faithfully," said Johnston, who works with the research team on the study — the third in a series on the issue. It was published in the peer-reviewed journal PLoS ONE.
"The question now is how hardwired is that? How likely are they to choose new areas (with more ice)?"
"We hope the animals are very flexible and that they can move north as we see less ice in the southern parts of their range. It's unclear how that will work and what rate at which they might be able to adapt."
If they do adapt and move to more northern regions to seek breeding grounds, it could work to the benefit of another animal — the polar bear — that is also having difficulty with sea ice levels.
Johnston said the challenges surrounding sea ice for harp seals and polar bears are critical to the population health of both, but are entirely unique of each other.
"It may actually bring more harp seals for polar bears to eat if they're forced farther north," Johnston said. "Both animals rely on sea ice, but the difference is polar bears rely on ice to have access to their prey . . . whereas for harp seals it's a breeding habitat issue. It's kind of works at different ends of the spectrum."
Another stark difference between the two, he said, is the current population health of harp seals compared to the dwindling number of polar bears.
Because similar studies on population health are often not conducted until numbers get to a more alarming rate, Johnston said investigating harp seals while they're numbers are still "robust" offers a rare chance to respond before things spiral out of control.
"We often wait until populations are depleted or in peril before we take action," he said. "This is a really nice situation where we can think ahead of time . . . so we're not backed into a corner where we're dealing with a train wreck. Often we don't see the signs until it's too late."
Original Article
Source: Canada.com
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