Sea otters were once in great abundance, with between 150,000 and 300,000 of them living in coastal waters from northern Japan to the Alaskan Peninsula and south to Baja California. The population of California's southern sea otter before the arrival of Europeans has been estimated at 16,000 to 20,000. Otters are among the few animals to use tools while feeding. They dive to the sea bottom, pull up a rock, place it on their bellies, and then, while swimming on their backs, use the rock as an anvil to break hard-shelled prey.

Their thick pelts made them prime targets for human hunters, however, and over-hunting eliminated the sea otter from San Francisco Bay some 150 years ago. In 1911, with the species on the brink of extinction worldwide, the International Fur Seal Treaty put some protections in place. The Marine Mammal Protection Act of 1972 and the Endangered Species Act of 1973 strengthened those protections. These measures saved the sea otter in California, allowing its numbers to increase from approximately 50 in the 1920s to 2,161 in 2001.

Currently, the greatest threat to the survival of the sea otter is a catastrophic oil spill. (The Exxon Valdez spill spread oil over an area much larger than the otter's entire California range.) Other threats include parasites and pollution, to which biologists attribute the recent dip in Bay Area sea otter numbers, as well as disease and entanglement in fishing gear. Some commercial fishermen are strongly opposed to the expansion of the sea otter population because the mammals consume significant amounts of seafood -- up to 25 percent of their body weight each day.

The absence of an important and once-flourishing species is an indication of how much work remains to restore the health of San Francisco Bay. Over time, however, if the sea otter continues to expand its current range to the north, it will return to the bay.

Reviving the Sea Otter Population
Successful recolonization in San Francisco Bay will depend on many factors, including:

• Healthy habitat. Sea otters need clean waters and a robust ecosystem to flourish.
  
  
• Enough food. Many of the shellfish, bottom-dwelling fish, and other creatures in today's San Francisco Bay are not native to its waters. That's particularly true of invertebrates, which would be a large portion of the sea otter's diet. It is impossible to know how well otters would adapt to such now-common species as the mitten crab and the Chinese clam.
  
  
• Good natural-resource management. Conflicts with human activities, including fishing and oil spills, are a constant threat.
  
  
• Protection of water quality. Sea otters eat shellfish, which often accumulate contaminants, including mercury, lead, copper, diazinon, dieldrin, and PCBs. At high enough levels, these contaminants could threaten the sea otters' ability to reproduce.
  
  

Previous    Next