Sea otters are staging a comeback along Canada’s North Pacific coast, but not everyone is happy about it.
The disappearance of otters, once trapped for their fur, allowed their food supplies — sea urchins, crabs and clams — to flourish. Now, otters threaten to deplete these profitable invertebrate fisheries, which have sustained coastal indigenous communities. But a new analysis shows that the benefits of bringing back otters may outweigh those costs, researchers report June 11 in Science.
With more otters and thus fewer kelp-grazing urchins, kelp forests can thrive, storing carbon and sheltering salmon, ling cod and other fishes. Plus, tourists will pay to snap photos of adorable otters snoozing on beds of kelp. In all, such increased sources of revenue could total $46 million Canadian dollars (equivalent to nearly $34 million in U.S. dollars on June 11) a year if sea otters fully recover along Canada’s Pacific coast, the study suggests.
Sea otters, which can grow as big as a medium-sized dog, were common from the Baja Peninsula to the Aleutian Islands of Alaska until the fur trade of the 18th and 19th centuries nearly wiped them out. As top predators in coastal ecosystems, these furry floaters gobble down a quarter of their body weight in urchins, crabs and clams each day.
Safe from the capable paws of otters, urchins and other invertebrates ballooned along the Pacific coast, both in body size and number, enabling profitable invertebrate fisheries and sustaining many First Nations communities that rely on this resource for food.
Since being reintroduced in the 1970s, this population of sea otters (Enhydra lutris) has grown from just thousands to about 150,000 by 2019, gradually reclaiming parts of their range and radically transforming these ecosystems. The otters’ resurgence comes at a significant cost — $7.3 million Canadian dollars a year — to the humans who depend on the otters’ prey, especially indigenous communities, which weren’t consulted in reintroduction plans. Rooted to the coasts they’ve inhabited for centuries, these communities, some of which are 50 kilometers from the nearest grocery store, can’t always easily shift to another source of food or business.
But the otters also affect positive change, too. It can be difficult to compare the clear loss of shellfish stock revenue to the more diffuse benefits of having more kelp and sea otters, says Inge Liekens, an environmental economist at Vito, a research institution in Mol, Belgium who wasn’t involved in the study.
“It’s easy to just focus on the negative, but this study does a good job broadening the view and incorporating biological, economic and social factors,” she says, and relating them to a common currency: money. Their framework is applicable to other ecosystems too, she says. “But some losses are emotional or cultural, and you can’t put those in the numbers.”
To tally benefits and losses in otter-free versus otter-full sites, the researchers compared total biomass, the sheer amount and diversity of biological material present. “The best-known effect of sea otters is an increase in kelp,” says Jane Watson, a marine ecologist at Vancouver Island University in Nanaimo. Kelp forests were on average 20 times larger in areas where sea otters have lived for decades on Vancouver Island, compared with bays where the otters were absent, Watson and her colleagues found. With fewer urchins, different kinds of kelp could thrive, creating a more diverse and resilient forest.
Robust kelp forests boost the overall productivity of the ecosystem by providing shelter and food to a whole host of organisms, including commercially valuable finfish like halibut and rockfish. Overall, biomass was 37 percent higher where sea otters thrived. Urchin, Dungeness crab and clam biomass fell when otters were present, but these losses were offset by gains in fish and other invertebrates that rely on kelp.
Using these biological data, the researchers developed a statistical model to estimate the range of possible payoffs of having otters around for fisheries, carbon sequestration and tourism. The team found that with the full recovery of sea otter populations along the Canadian Pacific coast, an increase in commercial fish such as salmon and halibut could provide $9.4 million Canadian dollars annually, while additional carbon stored by kelp forests equates to about $2.2 million Canadian dollars per year, based on European carbon market pricing.