Bringing Back Sea Otters Benefits People, Too

Science
جمعه 23 خرداد 1399 ساعت 22:46
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Smith sonian mag
Trappers and traders in the 18th and 19th centuries prized sea otters for their thick, waterproof fur—and the high prices they would bring. In 1890, for example, a newspaper reported that Russian noblemen who sought to adorn their overcoats with otter pelts were willing to pay nearly $45,000 in today’s money for a single pelt. And so the sea otter ( Enhydra lutris ), once common from the Baja coast of Mexico to the northern shores of Japan, was nearly hunted to extinction by the turn of the 20th century.
Over the past hundred years, thanks to conservation efforts, sea otters have now recovered across much of their historical range along the Pacific Coast of North America, but they haven’t always been welcomed back. The problem is that sea otters compete with people for the shellfish and urchins that moved in when the otter population were depleted, a conflict that has provoked debate about balancing the need protections for the otters with the economic impact of their presence in the coastal waters.
A study published today in Science finds that in economic terms, the otters' effect on their ecosystem—including increasing populations of fish, carbon capture and tourism—far outweigh the costs to the commercial shellfish fisheries with which they compete for tasty clams and crabs.
“The benefits are apparent to anyone who has spent a lot of time looking in the water,” says Edward Gregr, an ecologist at the University of British Columbia and lead author of the study. “But the need to monetize [these benefits] was becoming increasingly apparent.”
A group or raft of sea otters off the west coast of Vancouver Island, BC, Canada. (James Thompson Photography)
Hidden effects
In the years after otters were hunted to near extinction, now that a chief predator was gone, shellfish and sea urchins exploded in numbers up and down the coast. In addition to the commercial fisheries that formed to harvest the lucrative animals, coastal communities, many of them indigenous, increasingly relied on the seafood for sustenance. The spread of these invertebrates—particularly urchins, which feed on seaweed—came at a cost to kelp forests, which provide nutrition and habitat for diverse populations of fish and other creatures and store carbon, too.
As otter populations recovered, these changes worked in reverse as the otters’ doings as a top predator flow down through the ecosystem. Otters eat up to 30 percent of their body weight each day, and when they prey on lots of shellfish and urchins, kelp forests can regrow and give salmon and rockfish and others a place to stay.
But the competition for shellfish between otters and people creates tensions—sometimes even illegal culling. “People are pretty aware of public perceptions of otters, so nobody wants to come right out and say otters are horrible and we should get rid of them,” Gregr says. Behind closed doors, however, plenty of anti-otter sentiment persists; Gregr has heard them called the “rats of the ocean.”
Problems tend to arise anytime a predator recovers near where people live (reintroduced wolves are a notorious case). But while the predator’s tendency to eat commercially valuable fauna is easily quantifiable in economic terms, some of their intangible benefits go unquantified and are left out of the discussion.
“ The economic effect of predators in general, and otters in particular, has largely focused on competition for food, and conflicts with predator-prey interactions directly,” says James Estes, an ecologist at University of California, Santa Cruz, who is unaffiliated with the study. “And what this study shows is that those effects are much broader than that.” (Estes co-authored a comment on the study also published today in Science. )
To assess all the costs and benefits of the otters’ return, Gregr and co-authors created a model to compare the loss to commercial fisheries on the western coast of Vancouver Island due to otters—an estimated $7.3 million CAN each year—with the estimated value of the otters’ impact on the coastal ecosystem and economy. The resuscitated kelp forests were worth $2.2 million CAN annually for their carbon sequestration effects; increased fish populations supported by the kelp forests were worth $ 9.4 million CAN, and the annual increase in revenue from otter tourism was worth $ 41.5 million CAN. Taken together, the economic benefits of otters were seven times greater than the costs to commercial fisheries.
More than money
The assessment focused only on Vancouver Island, but the authors expect the results to be broadly applicable to ecosystems with sea otters along the Pacific Coast. However, Gregr noted that the assessment did not quantify every cost and benefit. It did not account for the effects of climate change or other factors, such as the impact of the COVID-19 pandemic on tourism, though the model takes pains to express the uncertainties inherent to ecological and economic assessments. Gregr sees this study as a “stepping stone” to more comprehensive economic models that account for ways predators change ecosystems—whether its otters, wolves, seals or dingos.
“Monetary values are just one way to think about and measure these sorts of changes,” Gregr says. “There's a whole basket full of non-monetary values—cultural values, social values that are very difficult to monetize.”
The inability of monetary value to describe the entire otter situation is particularly evident when considering coastal indigenous communities, who are likely to bear some of the highest costs and benefit the least from the otters’ recovery. (Even if it was all about money, she pointed out, it’s not clear the degree to which indigenous communities benefit from increases to tourism or fish populations.) Anne Salomon, an ecologist at Simon Fraser University, co-authored in May a survey of indigenous leaders on the impacts of otters on their communities.
“We found out pretty quickly and clearly that it's not about money for indigenous communities,” many of which count on shellfish and urchins for food security, Salomon says. “You can't eat dollar bills.”
Her survey found the most important factor in how indigenous communities felt about the sea otter’s recovery was the extent to which they felt agency or inclusion in decision-making. And they often have not been included. In the 1970s, for instance, the Canadian government introduced a population of sea otters near the Kyuquot/Chekleset First Nation’s traditional territory on Vancouver Island without consulting any Kyuquot/Chekleset people. Soon thereafter, the otter was listed as an endangered species, preventing Kyuquot/Chekleset people from hunting the otters as they traditionally had.
“If you go back in deep time on our coasts here, people have been facing the same issues for at least 14,500 years,” Salomon says. According to the archaeological record and indigenous knowledge-bearers, she says, people have managed the dynamic between sea otters, shellfish, and urchins ever since there were otters and people on the Pacific Coast. An economic assessment can add an important dimension to management, adds Salomon, but solutions that benefit everyone should involve Indigenous knowledge and possibly traditional methods of managing otters, such as allowing them to be hunted near the most productive beaches.
“We all need to come up collectively with a good solution,” said Daisy Hanson, a language and cultural worker and member of the Kyuquot/Cheklesaht Nation, who was interviewed for a project Salomon created to gather indigenous perspectives on the sea otter. “Because we can’t get rid of them all. That wouldn’t be human. That wouldn’t be right. But if we could have a little bit of control and have a little bit of say in how we utilize and live with the sea otters in our backyard. I just really hope for a better future for both sides: the sea otters and us— cu’ahs people.”
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