Longevity
Otters live an average of 10 to 15 years. Some individuals have lived more than 20 years in zoological parks.
Mortality for river otter pups has been estimated at about 32% in the first year, and 54% the second year (when most attain independence). Mortality drops after that, but less than one-quarter of all female otters survive long enough to reproduce.
Disease and Parasitism
Otters are susceptible to many diseases, and several have been reported in river otters, including kidney stones, tooth decay, and cirrhosis of the liver.
River otters are also susceptible to parasitic infestations by flukes, roundworms, tapeworms, and possibly ticks.
In the late 1990s the California sea otter population mysteriously declined. Many of the recovered and rescued animals had a higher than normal rate of parasitic, bacterial, or fungal infections that were probably major factors in the slow population recovery rate. The three most common parasites found in California sea otters are Toxoplasma gondii, Sarcocystis neurona, and Acanthocephalans.
Toxoplasma gondii (Toxaplasmosis) is a protozoan parasite that is found in a large number of stranded sea otters. This is the same parasite that cats can shed in their feces. T. gondii probably enters water systems by runoff from storm drains and from people flushing cat litter. This parasite lays its eggs in filter-feeding invertebrates, which are then consumed by sea otters. While not toxic to the invertebrate host, infected sea otters can develop encephalitis (infection of the brain) leading to seizures or even death.
Sarcocystis neurona is a protozoan parasite found in opossum feces. This parasite also lays its eggs in the otter's food source. Sea otters infected by S. neurona develop encephalitis.
Acanthocephalans, or thorny headed worms, are intestinal parasites of sea otters. Seabirds shed acanthocephalan eggs in their feces. The eggs are then ingested by invertebrates, which can then be consumed by sea otters. In sea otters, acanthocephalans puncture the intestinal wall and cause peritonitis (bacterial infection of the abdominal cavity).
Predators
Healthy adult otters have few predators. Very old otters and pups may fall prey to a number of land predators, including wolves, birds of prey, and large reptiles.
Surprisingly, one possible threat to the Alaskan sea otter population is predation by killer whales.
Scientists estimate that since 1990, killer whales have preyed on more than 40,000 Alaskan sea otters. It is believed that because of recent population declines of the killer whales' typical prey of Steller sea lions and harbor seals in the North Pacific, a small number of killer whales have shifted their main diet to sea otters.
Researchers estimate that a single killer whale can feed on up to 1,825 Alaskan sea otters in a year.
Killer whales do not currently pose a threat to California sea otter populations.
Sea otter carcasses in California have been found bearing wounds and tooth fragments identified as those of white sharks, but there is no direct evidence that white sharks consume sea otters. These findings suggest that white sharks may attack, but not prey on, sea otters.
The bald eagle is a significant predator of young sea otters in Alaska.
Human Impact
All otter species have been hunted for their thick, velvety fur. Excessive fur trapping during the 19th and 20th centuries caused severe declines in many populations.
During the 1976-77 trapping season 32,846 North American river otter pelts were reported taken in the U.S. The average selling price was $53 per pelt. In 1991-1992 more than 10,000 pelts were reported taken and sold for a much lower average selling price of $22.34.
Sea otters endured a long history of intensive exploitation. In 1741, Russians began hunting sea otters. They were joined by English and American hunters in the latter part of the century, and uncontrolled hunting continued until 1799. That year, some conservation measures were established, but unregulated killing resumed in 1867, when the U.S. purchased Alaska. During the 1880s, sea otter pelts on the London Market went for as much as $165, but by 1903 the price of a large, good quality pelt shot up to $1,125. By then the species had been nearly wiped out; probably only 1,000 to 2,000 survived worldwide.
Oil spills are devastating to sea otter population.
When crude oil penetrates the fur, it disrupts the interlocking arrangement of the underhairs and displaces the air layer. The fur loses as much as 70% of its insulation.
Otters may reduce heat loss by leaving the water, but unable to forage, starvation occurs rapidly.
When sea otters ingest crude oil they experience numerous severe physiological problems including anemia, shock, seizures, and hypoglycemia (low blood sugar), as well as damage to several internal organs. Toxic crude oil is particularly damaging to the liver.
In March 1989, 11 million gallons of crude oil spilled in Prince William Sound, Alaska. The spill resulted in the deaths of approximately 2,650 Alaska otters - a figure greater than the total California population. Scientists estimate that a similar spill off the Monterey Peninsula would destroy at least half of the California population.
In the mid 1970s and 1980s the California sea otter population declined as a result of sea otters drowning in nearshore, set gill nets. The population recovered slightly after the California Department of Fish and Game banned gill net fishing in shallow, coastal waters within the California sea otter's range.
Other threats to otters include pollution, habitat destruction, and persecution - commercial and game fisheries see otters as competition for resources.
