Weddell seal long-term study continues despite pandemic | Polarjournal
At birth, a newborn Weddell seal pup weighs only about 30 kilograms. Within five to six weeks, the pup grows to over 100 kilograms. Photo: Mike Lucibella, National Science Foundation

One of the few research teams that continued their projects despite the pandemic has been studying Weddell seals near the US McMurdo Station on Ross Island in Antarctica for decades. The team led by Professor Jay Rotella, an ecologist at Montana State University, is trying to understand what behaviors mother seals use to positively or negatively influence the later lives of their pups. An interruption in their research would have torn a big hole in the 52-year data series.

The pandemic is forcing many scientists to postpone their field research because of travel restrictions and the danger of introducing the virus into the few virus-free regions and research stations. But there are research projects that cannot simply be put on hold for a year or two. Some of these projects have collected a treasure trove of data, sometimes over many years or even decades, and it would be a great loss if the long-term series were interrupted. This includes the long-term study of Weddell seals in Antarctica’s McMurdo Sound, which are among the best-studied mammals on Earth thanks to decades of research. And so, last year, the American team decided not to interrupt the valuable data series and to continue its studies on the seals under the more difficult pandemic conditions.

Each year, all 500 to 600 newborn pups in the colony around McMurdo Station are counted, measured and tagged by scientists. Photo: Parker Levinson

The project provides important insights into the health of the Antarctic ecosystem in the face of climate change. Many other research groups rely on its data, and even a one-year interruption would do irreparable damage to the dataset, according to the research team. In order to continue the study during the pandemic, the size of the team was kept to a minimum. Likewise, the usual field camp had to be dispensed with and the work carried out from McMurdo Station.

Counting and tagging
The central focus of the project is population dynamics. In the past, Rotella and his colleagues learned a lot about how an animal’s body mass is related to its ability to survive and reproduce.
“The current project is about what does a mother do for her baby and how does that affect the baby’s prospects for surviving and producing offspring,” Rotella explains. His graduate student Kaitlin Macdonald adds, “We tag every single pup that’s born in the study area and that’s pretty much the most important thing we do. That allows us to know how many pups were born and it allows us to associate mothers with pups so we know what seals had a pup in a given year, and what females didn’t. That allows us to estimate reproduction rates and it also allows us to have known ages of individuals when those pups come back as adults.” The tags are a different color each year, so in subsequent years, when the young females return to their birthplace to give birth on their own, determining age and survival rates is easy. The scientists also record when the females first reproduce, when their reproductive rate is higher and when it is lower, and whether this changes over the course of their lives.

Each newborn gets a tag with a number that allows researchers to identify the animals individually even years later. The tag’s color is different each year to make age determination quick and easy. Photo: Mike Lucibella, National Science Foundation

Over the years, this has allowed researchers to build up a very accurate picture of the lives of Weddell seals and they are now able to assess what factors are affecting the population. “By keeping the data intact, we’re doing two things. Every year we know how that population is doing and how it’s responding to whatever the sea ice conditions were each year, and what was going on with fishing and other activities,” Rotella said. “We’re also putting lifetime reproductive histories together for all the females that were born in the study area.”

If the team had not been able to travel to Antarctica, the 500 to 600 newborn seals would have remained untagged last year and subsequent age determination would have been impossible. This would have meant an irretrievable loss for the data set.

“This project has been collecting data this way since the 1960s and it’s one of the longest-running projects on a long-lived mammal in the world. [Sie sind] a sentinel of the Southern Ocean, a bell wether for how the ecosystem is doing.”

Professor Jay Rotella, project leader and ecologist at Montana State University, Bozeman, MT, USA

Understanding how seals respond to environmental change and what that says about the health of the ecosystem that surrounds them has taken on added impetus as the sweeping changes associated with climate change begin to manifest across the icy continent.

Professor Jay Rotella has been project leader of the long-term study since 2002. With his team, he spends six weeks each year with the Weddell seals. Photo: Mike Lucibella, National Science Foundation

Nothing different for the Weddell seals
For the seals, the world continues to turn as before. As they do every year, the mothers were lying on the sea ice with their pups when the researchers arrived at the station. “It’s interesting to see the colonies just kind of keep going on. They don’t know a pandemic is happening,” Macdonald said.

The scientists, on the other hand, had to accept some limitations. With three researchers, the team was only half as large as usual and the workload was correspondingly higher for each individual, despite neglecting less important aspects. In addition, they could not set up the camp on the sea ice and thus had to drive several hours a day by snowmobile to the seal colony.

Weddell seals resting at a distance from each other on the frozen Ross Sea. Photo: Tien Lai, National Science Foundation

Regardless, the sea ice situation was different than in previous years. The ice was not as thick and the ice edge was much closer than usual, so there was a lot of open water near the colony. Still, the researchers were pleased with the conditions. “This year is a fantastic year to be there from a science perspective, because we have the least ice we’ve had in the time we’ve been on the project, and one of the lowest ice years ever since the late 1970s,” Rotella said. “Getting data for how the population responds in a year like this is really excellent for adding to our ability to see how seals respond to changes in the environment and so we’re really fortunate to be able to be there in a year like this.”

The first results of the last years show that young mothers lose more weight during the rearing of their pups than animals at prime age; the mass transfer thus becomes more efficient with increasing age. This could be due to the fact that females giving birth for the first time are not yet fully developed physiologically. On the other hand, the researchers found only a weak correlation between the weight of the young at weaning and the age of the mother.

Even though not all investigations could be continued to the usual extent last year, Rotella and his team were able to collect the most important data and thus keep the long-term study alive without major gaps.

Julia Hager, PolarJournal

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