Bringing otters back really paid off.

Science News breaks down the costs and benefits of restoring a predator like otters to an ecosystem, and finds that the ecological conservation approach pays for itself and then some (unless you happen to eat the same shellfish otters do):

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.

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.

You can read the study in Science here.