Pollution Kills California Sea Otters

Exceptionally high levels of PCBs have been measured in sea otters that died along the California coast of infectious diseases, suggesting that accumulating toxins compromised the mammals' immune systems. Marine pollution seems to be why populations of the California subspecies of sea otter have not rebounded to the extent their relatives to the north have.

Female sea otters picked up dead or dying off of beaches from San Francisco to Santa Barbara between 1992 and 2002 were all contaminated with toxins, although concentrations varied enormously among individuals. Those otters with the highest levels of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in their livers also had other characteristics in common.

Many otters had enough PCBs to interfere with their physiological functioning. The greatest PCB concentrations were in sea otters that died of infectious diseases.

Often dead sea otters also showed obvious signs of starvation. The most severely emaciated animals had the highest levels of PBDEs and PCBs. This points to the toxins ultimately interfering with normal physiological processes involving the breakdown of fat.

The findings help explain why this sea otter subspecies has such unusual population dynamics. Among the hundreds of otters found dead on California beaches, an unusually large percentage, 40 percent, have succumbed to infections caused by bacteria, parasites or fungi. Instead of mainly the young and aged dying, most diseased otters are adults that should be in their prime.

These animals are exceptionally contaminated with pollutants. Although PCB levels declined somewhat over the decade, they still were found in the sea otters at concentrations well above those reported in most other marine mammals around the world. PBDEs had also accumulated in sea otters from the entire study period at levels often greater than those detected elsewhere in marine mammals.