Saving fur seals could wipe out Antarctica’s endangered plants

This article was originally featured on Hakai Magazine, an online publication on science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.

The seal population is booming in Antarctica. After being nearly wiped out by hunters in the early 20th century, Antarctic fur seals recovered as they made their way to new frontiers. Their recovery has been so successful that the animals are exceeding their known historical range, causing “unanticipated terrestrial challenges for the protection of Antarctica’s vulnerable vegetation,” warns a recent study.

Since about 2010 fur seals have been spreading from their center on the island of South Georgia along the Antarctic Peninsula and reaching the south side of Marguerite Bay. “That’s a lot further south than we would have seen them before,” says Peter Convey, an ecologist with the British Antarctic Survey and lead author of the new study. This expansion is mainly led by juveniles and non-breeding males. When they come ashore, these fur seals trample the fragile coastal vegetation that thrives on Antarctica’s limited ice-free terrain.

Convey points to the damage caused by fur seals on Signy Island, one of the South Orkney Islands, where the landscape, including the fragile mosses and lichens that grow there, has been badly affected by seals. In 1977, says Convey, there were about 1,600 seals on Signy Island. In the mid-1990s it was over 20,000. In addition to trampling on vegetation, seals defecating and urinating near the island’s freshwater lakes have contributed to their eutrophication.

Convey and his colleagues address the issue to stimulate discussion. He is concerned that the current plans overseeing the protection of Antarctica – administered through the multi-state Antarctic Treaty – only consider the human impact on the continent. But for him, the magnitude of the seal’s impact far outweighs that of humans. Convey says the situation leads to a fundamental question: is the Antarctic Treaty’s job to physically protect the continent’s inhabitants from each other? “There’s no easy answer,” says Convey. But he believes it’s a debate that needs to be had.

Brian Silliman, a marine biologist at Duke University in North Carolina who was not involved in the research, suggests that the seals’ spread may be a case of reintroduction throughout their historical range. When looking at recovering species, it’s common to think that they’re “doing things we thought they shouldn’t be doing,” says Silliman. Studying populations at their nadir after decades of overhunting or loss can give a false impression of their past range and behavior, he adds.

It is unclear what the population of Antarctic fur seals was before historic overhunting, or where exactly they were distributed. However, Convey stresses that there is no evidence that seals ever padded across these particular shores – even before they were exploited.

Convey is emphatic that seal culling is not and should not be on the table. But how to respond to the exploding fur seal population is a management headache and requires difficult decisions. The core question is whether Antarctica’s terrestrial ecosystems should take precedence over the encroaching fur seals.

Claire Christian, executive director of the Antarctic and Southern Ocean Coalition, an NGO dedicated to protecting Antarctica and its surrounding waters, says the Antarctic treaty system has to make tough decisions based on fairly limited information. A possible approach could be the identification of vegetation hotspots that should be protected from roaming fur seals. Convey agrees that this is a possible solution. However, taking action to protect this terrain – such as erecting fences – would be another human intervention with potentially unforeseen consequences. Fences have been erected in some places, with mixed success.

Another approach, Christian suggests, is figuring out what it takes for this new normal to thrive, “rather than trying to make it what we want to see,” she says.

Ally Kristan, a marine biologist who studied recovering populations on South Georgia Island while at Louisiana State University and was not involved in the research, is “very cautious about using control methods on a population that is already so severe and catastrophic by human influences.” Regardless of where they used to live, fur seals are now in a changed ecosystem due to past and current influences, says Kristan. There’s no way to make things “normal” again, she adds.

This lack of simple answers unites those working to protect Antarctica with those working elsewhere to cope with changing environments, such as in the Indian Ocean, where dwindling shark populations have allowed green sea turtles to recover quickly – and to overgraze seagrass meadows. Along the west coast of North America, recovering sea otter populations have come into conflict with local populations. As other marine predators recover, they may do likewise.

Inadvertently or not, humans have been picking ecosystem winners and losers for millennia. As populations recover from historical exploitation and struggle to adapt to already changing environments that continue to change due to anthropogenic warming, a hands-free approach seems less and less viable.

This article first appeared in Hakai Magazine, and is republished here with permission.

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