California sea lions probably live an average of 15 to 25 years. California sea lions in zoological habitats have been known to live 30 or more years.
Pup mortality may be 10% to 15% during the first month. Pups may be abandoned, wash away from pupping areas during high seas, or become ill during their first year.
As a California sea lion ages, it periodically produces growth layers of dental material. Age can estimated by examining the growth layers of dentine in the roots of the canine teeth.
Predation is not a significant threat to healthy adult California sea lions. Killer whales and large sharks occasionally prey on weaker California sea lions. A Steller sea lion bull was recently observed preying on a California sea lion pup.
Hunting by Humans
- More than 7,000 years ago, California sea lions were hunted by the Chumash and Nicoleño Indians on the Channel Islands for subsistence. In the late 1800s they were hunted commercially for their hides. The impact of harvesting on sea lion populations has never been clear; it may have caused a slight decline.
- In 1899 the United States Fish and Game Commission concluded that California sea lions were too numerous, and several thousand were killed intentionally for bounties. Killing sea lions in the Santa Barbara Channel was banned in 1909, but indiscriminate killing continued.
California sea lions continue to be shot by fishermen over competition for fish, particularly salmon. California sea lions often are seen in salmon spawning grounds, but in some cases, eat more lampreys than salmon. Lampreys (a type of fish) are parasites of salmon.
Pesticides and heavy metals in the ocean may impact sea lions. In one study, the tissues of females that had aborted pups had much higher concentrations of DDT than females who carried their pups to term.
Marine debris is a threat to sea lions. They can become entangled in nylon fishing nets or plastic packaging materials, causing severe injury or drowning. Sea lions also ingest plastic debris, which can cause obstructions in the digestive tract.
Disease and Parasitism
California sea lions are susceptible to gastric disorders, viral, and bacterial infections. Leptospirosis is a type of bacterial infection commonly found in California sea lions. Leptospirosis primarily attacks the kidneys and can lead to permanent kidney damage, kidney failure, and even death.
California sea lions are host to a variety of parasites. Internal parasites include those that infect the respiratory tract, heart, liver, and stomach. One such parasite, the lungworm, Parafilaroides decorus, is ingested by sea lions when they feed on opaleye, a host fish for the lungworm. External parasites include lice, mites, and ticks.
In 1982, 1993, and 1998 marked declines in sea lion numbers was attributed to El Niño events. This cyclic event is characterized by a number of atmospheric changes, including an unusually warm current that prevents the upwelling of nutrient-rich cold water and causes fish populations to shift. A 25% to 35% decline in birth weights in the Channel Islands during this time was also traced to El Niño, which caused poor nutrition in pregnant and nursing females.
Domoic Acid Toxicity
Domoic acid is a naturally occurring toxin produced during harmful algae blooms (red tides) by phytoplankton of the genus Pseudonitzchia. Sea lions and other marine mammals develop neurological problems and even die after consuming anchovies, sardines, and shellfish containing this biotoxin. Since the late 1990s, hundreds of sea lions have stranded due to domoic acid poisoning.