A sea otter and her pup in California’s Morro Bay. Photo: Anchor Lee
By 1911, sea otters had almost been hunted to extinction. Prized for their rich fur pelts, populations dwindled to less than 2,000 individuals, less than one percent of their original global population, spread out across eleven isolated groups in Russia, Alaska, and California. Unsurprisingly, the removal of the sea otter had cascading effects on the ecosystems in which they once thrived.
According to a new study published on Nature.com, the recolonization of sea otters into their traditional habitats slows down the erosion of salt marsh edges in estuaries. The study observed the wetlands of Elkhorn Slough in California’s Monterey Bay and found that the otters’ predation of burrowing crabs led to strengthening of the marshes’ edges and reduced erosion.
The burrowing crabs dig into the marsh banks, compromising its structural integrity. Eventually storms or large swells can cause these banks to collapse. Along with analyzing erosion rates since the 1930s, researchers isolated several marsh creeks from the sea otters for three years and found that those creeks with sea otters eroded at slower rates than those without sea otters.
Sea otters first returned to Elkhorn Slough in 1984, in part due to the Monterey Bay Aquarium’s program for raising and releasing orphaned otters. Otter populations, between the northern and southern subspecies, once ranged from Baja California, Mexico all the way north to Alaska, and across the Pacific to Russia and the northern islands of Japan. Today, the southern sea otter is found only on the Central Coast of California, while the northern sea otter is found in areas of Washington state, Canada, Alaska, Eastern Russia, and Northern Japan.
While populations are stable and slowly growing, the sea otter is still protected under the endangered species act and incredibly vulnerable. The Monterey Bay Aquarium says an oil spill is the biggest threat to sea otters, given that the southern subspecies in particular lives in a relatively small geographic area.
The study bolsters the arguments that predators have cascading effects on the vegetation of their ecosystem. The researchers compared their findings to the famous example of how the reintroduction of wolves in Yellowstone National Park reduced the erosion of stream banks, among other improvements.
