Could San Francisco Bay help the sea otter thrive?
1-million-acre bay has food — crabs, clams, mussels, worms — and fewer sharks
“The idea with reintroduction is to put otters back in an area where they used to be. From the aquarium’s side, it’s one of our main goals to contribute to sea otter recovery in California.” — Jessica Fujii, assistant manager of sea otter research At the Monterey Bay Aquarium
When most people think of California sea otters, the kelp beds of Monterey Bay and Big Sur’s rocky shoreline often frame the backdrop.
But an increasing amount of scientific research is suggesting that if the fuzzy, frolicking mascots of the Central Coast are ever going to expand their population enough to be removed from the endangered species list, some of them may need to be relocated north, to a new home inside the protected confines of San Francisco Bay.
It’s a place they haven’t inhabited for nearly 200 years, but some fishermen might not be ready to welcome them back.
The otters, whose population has stalled in recent years at around 3,000, are stuck. They can’t expand their coastal range any farther north than Pigeon Point in San Mateo County because the area is thick with great white sharks. When the otters try to swim through what marine biologists call “the gauntlet,” they are regularly bitten and often don’t survive. The thinking: What if several dozen otters were moved under the Golden Gate Bridge into the bay? Could they flourish, reproduce and spread to a new part of the state?
“In order for the population to increase they need to expand into more territory,” said Jane Rudebusch, a marine researcher with San Francisco State University. “White sharks are preventing that from happening.”
A new study published this week found that some parts of the bay would be safer for otters than others.
The research analyzed hazards — including large commercial ships, high
speed ferries, oil spills, fishing gear and toxins such as mercury. The areas with lowest risk are in the North Bay, including San Pablo Bay National Wildlife Refuge and China Camp State Park near San Rafael, the study found, and in the South Bay, particularly the Don Edwards National Wildlife Refuge. Big cities, ports and heavily trafficked areas, such as the Golden Gate and Bay bridges, and the Oakland waterfront, pose the highest risk.
“San Francisco Bay is a busy place with a lot of things going on,” said Rudebusch, lead author of the study. “For sea otters to succeed, it’s definitely a challenge. Ultimately, the sea otters will show us if it is possible for them to re-colonize the bay. But the potential is definitely there.”
The concept is still in the early stages. To happen, it would require approval from the U. S. Fish and Wildlife Service, and probably several state permits.
But there is a growing momentum, with backing from prominent institutions such as the Monterey Bay Aquarium.
“The idea with reintroduction is to put otters back in an area where they used to be,” said Jessica Fujii, assistant manager of sea otter research at the Monterey Bay Aquarium.
“From the aquarium’s side, it’s one of our main goals to contribute to sea otter recovery in California,” she said.
The aquarium has proved that otters don’t need rocky shorelines and kelp forests to thrive. Every year, its scientists take in several orphaned sea otter pups whose mothers have died or been separated. Using “surrogate mother” otters that live at the aquarium, the orphans learn how to feed, groom and socialize.
The aquarium has released dozens back into the wild, most notably at Elkhorn Slough, an estuary near Moss Landing full of tidal marshes, creeks and muddy channels — similar to San Francisco Bay. From 2002 to 2016, the aquarium released 37 otters there. Of those, 31 stayed in the slough. They found food. They reproduced. And they have flourished.
Setting up a similar program in San Francisco Bay could be five to 10 years away before all the studies and permits are completed. But the 1-million-acre bay has enough food — crabs, clams, mussels and worms — to support up to 6,600 otters, a major study last December found.
“It would essentially end up lifting the sea otter out of its endangered species status,” said Brent Hughes, assistant professor of biology at Sonoma State University and lead researcher in that study. “For the conservation of the sea otter, this would be huge.”
But there are political challenges. Sea otters eat 25% of their body weight a day. Many of the species they eat, such as Dungeness crab, are prized by commercial fishermen. Dungeness crab was a $51.8 million fishery last year, said Mike Conroy, executive director of the Pacific Coast Federation of Fishermen’s Associations in San Francisco.
“The question that should be addressed before we buy into this is what impact will it have?” Conroy said. “Will it result in negative impacts to other species? I don’t think we know yet.”
Historically there were about 16,000 sea otters from the Oregon- California border to the Baja peninsula in Mexico. But they were hunted relentlessly in the late 1700s and early 1800s by Russian, British and American fur traders for their pelts, which are denser and softer than mink fur. Many lived in San Francisco Bay, but by the Gold Rush, they were all but gone.
They were feared extinct until the 1930s, when about 50 were discovered in remote Big Sur coves. Protected by the Endangered Species Act in 1977, they began a slow comeback. Over the last decade, however, the number of shark attacks on otters has grown. Some researchers think it’s because federal laws have protected elephant seals, sea lions and other marine mammals that the sharks eat, growing their numbers.
Scientists believe that otters in San Francisco Bay would increase tourism and could expand the number of fish.
That’s because they eat crabs, which eat sea slugs, which in turn eat algae on eel grass. When the number of crabs drops, the sea slugs expand in number, and they eat more algae, allowing the sea grass — where young fish hide — to flourish. But there are many unknowns, from whether transplanted otters would stay in the bay to how they might handle a crowded area with 8 million residents.
“They were in San Francisco Bay historically,” Rudebusch said. “There’s a great interest in restoring this animal to an ecosystem that has been missing one of its key parts for more than 150 years. To put the missing link back would be fascinating.”