Study: Weddell seal reproduction dropped to unprecedented low during unusual Ross Sea ice events

A Weddell seal at a breathing hole. Photo courtesy NOAA.

Overall population remained stable, but emperor penguins the region hit hard by thin sea ice and shifting icebergs

By Summit Voice

SUMMIT COUNTY — Dramatic changes in Antarctic sea ice extent and thickness had different impacts on species that breed along the edge of the Ross Sea, with Weddell seals weathering the changes well, while emperor penguins suffered population losses.

A team of Montana State University ecologists who recently published their findings from last year’s observations are headed back to Antarctica to continue their Weddell seal research as part of an important long-term effort to monitor ecological changes in the region.

Last year, the scientists found ice that was only three feet thick instead of the usual 12 to 16 feet in the Erebus Bay region of the Ross Sea, according to co-author Bob Garrott. Large cracks and active breaks threatened snowmobile travel. As a result, the faculty members and students moved their base camp to a safer spot and set up emergency camps around their study area. When they couldn’t cross the ice on snowmobiles, they flew by helicopter.

In the course of their work the researchers saw how the Weddell seals faced challenges from massive icebergs that broke off and dramatically changed sea-ice conditions in a number of recent years, said researcher Jay Rotella.

Data from 29 years of monitoring showed that reproduction dropped to unprecedented lows during the peak of the iceberg event, but that the overall population appeared stable, as the seals adapted to changing conditions by lowering their breeding efforts during years of iceberg presence. The seals tended to avoid breeding colonies when sea-ice conditions were particularly unfavorable.

By contrast, emperor penguins continued normal activities during the worst of the iceberg event. The result was dramatic, with dying penguins, as well as breeding failures, Rotella said. Moving ice crushed eggs and even some adults at the peak of the iceberg event. Exhaustion and starvation might also have been an issue for penguins that walked across the ice from open water to their nesting colonies.

“These results reveal that, depending on their ecology, different species can suffer different impacts from an extreme environmental disturbance,” said Rotella, the new leader of the Weddell seal study.

“The results also reveal the importance of having long-term data to evaluate possible effects,” Rotella continued. “Without the data, we couldn’t have known whether this extreme environmental event had extreme consequences for the seals or not. Fortunately for the seals, it did not. We learned that the seals were quite capable of riding out the massive changes in ice conditions as long as they didn’t persist too long.”

Rotella said the thicker sea ice provides protection from predators like orcas and leopard seals. It also serves as a platform for Weddell seals in the first few weeks of their lives when they have little fat for staying warm in the water and can’t swim well yet.

When the ice is thinner, predators have better access to the breeding areas used by penguins and Weddell seals for rearing their young. It is also easier for storms to shatter the ice sheets and for the area to have open water.

To make the research accessible to the public the team maintains a Weddell seal blog and also provides video updates on YouTube.

Price will again produce a variety of videos and other materials that will be available to the public. For more information, go to the video blog at http://inmotion.typepad.com/weddell_seal_science and the YouTube channel at http://www.youtube.com/user/WeddellSealScience.

This will be the 45th season for the study that Garrott and Rotella took over around 2001 from Don Siniff at the University of Minnesota. Initiated by Siniff, the study is one of the longer running animal population studies and the longest marine mammal study in the southern hemisphere. It not only focuses on changes in the Weddell seal population, but it yields broader information about the workings of the marine environment. The study incorporates information on sea ice, fish, ecosystem dynamics, climate change, and even the Antarctic toothfish, which is marketed in U.S. restaurants as Chilean sea bass.

The MSU study concentrates on pups and adult breeding females that live in the Ross Sea, which is the most pristine ocean left in the world and the only marine system whose top predators – including the Weddell seal – still flourish.

The researchers start the season by weighing and tagging every pup when it’s about two days old. Later in the season, they visit every colony in their study, collecting genetic samples and recording every tag they find. Weddell seals are relatively gentle for being a top predator in the ecosystem, but they can weigh over 1,000 pounds and have a set of teeth like a bear’s, Garrott has said in the past.

The paper describing last year’s observations was published Sept. 26 in the international journal, “Proceedings of the Royal Society B: Biological Sciences.” Lead author was Thierry Chambert, a doctoral student supervised by co-authors Bob Garrott and Jay Rotella in the MSU ecology department. Rotella and Garrott have just received a National Science Foundation grant for $867,272 that will extend their long-term study by five more years.

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