This article originally appeared on hakai Magazine, an online publication on science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.
In Antarctica, the sea lion population is booming. Having recovered from near eradication by hunters in the early 20th century, Antarctic fur seals are making their way to new frontiers. Their recovery has been so successful that the animals are outgrowing their known historical range, causing “unexpected terrestrial conservation challenges” for Antarctica’s fragile vegetation, a new study warns.
As of 2010, fur seals have expanded from their center on South Georgia Island to the Antarctic Peninsula, reaching the southern side of Marguerite Bay. “That’s much 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 led mainly by juveniles and non-breeding males. When they come ashore, these fur seals trample the fragile coastal vegetation that thrives in the limited ice-free terrain of Antarctica.
Convey points to the damage fur seals have caused 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, Convey says, there were about 1,600 seals on Signy Island. By the mid-1990s, there were more than 20,000. In addition to trampling the vegetation, seals that defecate and urinate near the island’s freshwater lakes have contributed to its eutrophication.
Convey and his colleagues are raising the issue to stimulate discussion. He worries that current plans overseeing the protection of Antarctica, administered by the multi-state Antarctic Treaty, only take into account human impacts on the continent. But to him, the scale of the seal’s impact far exceeds that of humans. Convey says the situation raises a fundamental question: is it the job of the Antarctic Treaty to provide physical protection for the continent’s inhabitants from each other? “There’s no easy answer,” says Convey. But he believes that it is a debate that must be had.
Brian Silliman, a marine biologist at Duke University in North Carolina who was not involved in the research, suggests that the expansion of the seals may be a case of recolonization over their full historical range. When looking at bouncing species, it’s common to think they’re “doing things we thought they shouldn’t be doing,” Silliman says. 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 levels of Antarctic fur seals were, or where exactly they were distributed, prior to the historical overhunting. Convey, however, stresses that there is no evidence that seals made their way through these particular shorelines, even before they were exploited.
Convey is careful to emphasize that culling the seals is not and should not be on the table. However, the question of how to respond to the growing population of sea lions is a management headache that requires difficult decisions. In essence, the situation calls into question whether Antarctic terrestrial ecosystems should take precedence over expanding 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 difficult decisions based on rather limited information. Potential identification of vegetation hotspots that need to be protected from roaming sea lions may be one approach. Convey agrees that this is a possible solution. However, taking measures to safeguard this land, such as installing fencing, would be another human intervention with possibly unforeseen consequences. Billboards have been deployed in some locations, with mixed success.
Another approach, Christian suggests, is to figure out what it takes for this new normal to thrive “rather than trying to make it what we want to see,” he 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 wary of implementing control methods in a population that has already been affected so greatly and disastrously by human impact”. .” Regardless of where they used to live, Kristan says, fur seals now find themselves in an ecosystem altered due to past and current impacts. There’s no way things are going back to “normal,” she adds.
This lack of simple answers unites those who care about protecting Antarctica with those who work to manage changing environments elsewhere, such as in the Indian Ocean, where declining shark populations have allowed green sea turtles to recover rapidly. and overgraze on seagrass beds. Along the west coast of North America, recovering sea otter populations have come into conflict with the local population. As other marine predators recover, they may do the same.
Inadvertently or not, humans have been picking the winners and losers of ecosystems for millennia. As populations recover from historical exploitation and struggle to adapt to already altered environments that are further changing due to anthropogenic warming, taking a hands-off approach seems less and less feasible.
This article first appeared on hakai Magazine, and is republished here with permission.