Washington (AFP)

Otters, reintroduced off Vancouver on Canada's Pacific coast in the 1970s, devoured the crustaceans on which local fishermen depended, but a new kind of analysis shows that the economic benefits are, in reality, positive for the region.

The study, conducted by researchers from the universities of British Columbia and Vancouver Island and published Thursday in the journal Science, is interesting because it could serve as a model for other large hated, exterminated or disappeared predators, whose there are fears that reintroduction will cost local farmers or breeders dear: wolves or bison, for example.

Here is the cascade of events for otters in the Pacific. At the end of the 19th century, they were hunted for their fur until almost extinct.

As otters feed on crustaceans (they must eat a quarter of their weight each day), the population of these invertebrates exploded during their absence, giving rise to a thriving crustacean fishing industry.

In the 1970s, it was decided to reintroduce the otter. Local populations, including Aboriginal First Nations, were not consulted. The otters began to eat crustaceans, which were the livelihood of these fishermen: a typical example of ecological-economic conflict.

But the effect is more profound, say and demonstrate the researchers by speaking of "cascade". Otters also eat sea urchins, but sea urchins devour the forests of seaweed and sea grass called kelp. The size of these algal forests has been multiplied by 20, estimate the researchers.

These algae are protective habitats for many species of fish, such as herring. Which, in turn, benefits fishermen from these fish.

- Wolves, foxes and ticks -

The biggest dollar benefit is tourism: "Otters are a very charismatic species. Tourists love to watch them in the wild, and they're willing to pay for the experience," says Russell Markel, co -author of the study and operator of Outer Shores Expeditions.

And that's without counting the ecological benefits like the absorption of additional carbon.

In total, the team estimates, the profits in dollars are seven times greater than the losses for the shellfish fishery.

"When you restore a predator, it's often controversial, since usually predators compete with people for resources," says Jane Watson, professor at Vancouver Island University.

But the return of algae "increases productivity near the shore, it creates habitat for species dependent on kelp," she said.

"Countless ecosystems around the world are just a shadow of their past glory," said Kai Chan of the University of British Columbia. "The reintroduction of wolves can trigger a chain of beneficial effects for a large number of species, and for humans in the United States or Europe."

How could the return of wolves benefit humans? Their extermination in the western United States favored the coyotes, which in turn reduced the population of foxes: now the foxes ate small mammals, whose population therefore exploded ... causing an increase in ticks, and Lyme disease.

Researchers say you need to take this chain of effects into account, along with other factors depending on regional ecosystems, to calculate the net cost of returning wolves, not just the cost of livestock eaten by predators.

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