After being hunted to near extinction in the 19th century, sea otters from southeast Alaska to central California have made a remarkable recovery. But it’s one that is causing anxiety for those who make their living harvesting sea otters’ prey, including Dungeness crabs. While it has long been assumed that a steadily increasing population of sea otters would lead to lower crab catches, a new study shows that—in California at least—that’s just not the case.
Instead, says Andre Boustany, the lead author of the new study and a fisheries scientist with the Monterey Bay Aquarium in California, Dungeness crab landings have actually been increasing in areas that have sea otters. “It doesn’t seem like they have a measurable impact on crab populations.”
The study assessed commercial Dungeness crab landings in California ports from 1980 to 2018, breaking out three regions with sea otters: Half Moon Bay, Monterey Bay, and Morro Bay. Boustany says that despite the presence of sea otters, Dungeness crab populations are increasing in those areas because of improving environmental conditions that are more favorable to larval crabs. Similarly, he says, the decreasing Dungeness crab harvest in Northern California ports, where there are no sea otters, is likely due to climate change and higher levels of ocean acidification.
While sea otters are ravenous eaters—every day they consume around 25 to 30 percent of their body weight—Dungeness crab is not exactly their favorite food. Based on observing 117 otters conduct 57,186 feeding dives, the scientists found that Dungeness crab makes up as little as 1.6 percent of a sea otter’s diet on average.