New research indicates that young harp seals cannot cope with the rapidly changing climate.
The scientists base their conclusions on a study in Saint Lawrence Bay. Harp seals come together to give birth to their young. The only problem is that the harp seals use ice for this: they give birth on sea ice. And that is rapidly declining.
To map the consequences, the researchers first studied satellite images of the area. The images covered the years 1992 to 2010. Then it was examined whether there was a connection between the images (which showed the development of the ice) and the number of reports of dead harp seal pups. It also looked at what influence the North Atlantic Oscillation (NAO) had on the situation. The NAO has a major influence on winter weather and the formation of ice.
The researchers found a strong connection. In years with less sea ice, the number of dead harp seal pups increased sharply. The same applied to years in which the NAO was weaker. The NAO appeared to have contributed greatly to the enormous decline that the harp seal experienced between 1950 and 1972. But the NAO was probably also responsible for the recovery that the harp seal was allowed to undergo between 1973 and 2000.
That seems good news: in the past the harp seal was able to recover well from the consequences of the NAO. Then should that also succeed in the future? The scientists wonder. The situation that the harp seals are currently dealing with does not only concern the NAO. "Our models show that the sea ice in this area decreases by six percent every decade during the period of our research," says researcher David Johnston. And that is independent of the NAO and has everything to do with global warming. If the NAO then causes a somewhat colder winter in which more ice can arise, more harp seals will manage. But: "The losses in bad years are greater than the profits in good years".
"The death rate we see in eastern Canada is dramatic," Johnston emphasizes. "In years with little sea ice, entire volumes disappear: practically all puppies die." And that makes the researchers think. Because how much can such a population actually have? "The species is well able to deal with natural climate changes in the short term, but our research suggests that they are not as well able to cope with the effects of short-term changes and long-term climate change and human influences such as hunting and by-catch. "
It seems that some harp seals choose eggs for their money. They have looked for a new place to give birth to their young. But thousands of harp seals do not have that presence of spirit and continue to come to Saint Lawrence Bay. And many puppies are lost there every year. And it can take years for the species to recover from that loss, the researchers conclude in the magazine PLoS ONE.