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. 

The biggest monetary payoff from
sea otters was from increased tourism. The researchers combined park visitation
data with surveys detailing people’s willingness to pay to see otters, and estimated
that otter-dominated ecosystems could generate an additional $41.5 million
dollars a year in tourism revenue.

Of course, there is a lot of
uncertainty around these estimates. Tourism can dry up due to unforeseen events
(like the COVID-19 pandemic). And
market prices for fish can change with demand. But the researchers present a
range of possible futures, and in all scenarios, the benefits outweigh the lost
revenue from shellfish harvesting. 

This study represents “a beacon of
hope,” says coauthor Kai Chan, a conservation scientist at the University of
British Columbia in Vancouver. “It shows that when people invest in restoring
ecosystems, including by restoring top predators like sea otters, it can have
large positive benefits for people,” though he and his colleagues acknowledge
that those benefits won’t always be shared equally.

“This is a beautifully done study,” says Anne Salomon, a marine ecologist at Simon Fraser University in Burnaby, Canada. But she notes it doesn’t factor in the effects of climate change, which threatens kelp forests with more frequent and intense ocean heat waves (SN: 4/10/18). Nor does it account for the deep history between sea otters and First Nations communities. For thousands of years, sea otters enabled rich kelp forests in some areas, and indigenous communities managed productive shellfish beds through traditional hunting practices. The researchers “start from this assumption that historically the coasts weren’t exploited, but that’s not the case,” she says.

Moving forward, “indigenous
communities need to have the collaborative authority with federal governments
to manage their relationship with sea otters,” Salomon says, which could lessen
the costs for indigenous communities. “Incorporating traditional knowledge can
help us maintain resilient otter and kelp populations as well as shellfish
fisheries,” she says. “We can have both.”