California Sea Lion

The California sea lion is a highly gregarious species, hauling out in large groups, although tending to feed individually or in small groups, unless large quantities of food are present. They feed on a large number of different fish species (including some commercial species), such as northern anchovies, pacific whiting, mackerel and are known to also take some cephalopod species. Dives usually last about two minutes, but can last up to ten minutes, and average depths of 26 to 98 metres, although California sea lions have been known to dive to well below 200 metres (2). The breeding season starts in May, at which time adult males begin to fight for a territory. Most males are unsuccessful and retreat to the sea, or to bachelor beaches nearby. Successful males guard their territory and maintain boundaries with routine displays and frequent barking. A male may maintain his territory for up to 45 days depending on other competitive males and on fat reserves. Females give birth to a single pup throughout May and June and are ready to mate again about 28 days after giving birth, although this interval is more variable among the population in Mexico. The mothers spend the first week after birth with their pup and then begin alternating feeding trips at sea (two to three days) with suckling bouts on land (one to two days), until the pup is weaned, at about ten to twelve months. The mothers and pups recognise each other after separation by sound and smell (2). The breeding season ends in August after which time most males migrate north and the females and juveniles disperse, but stay close to the breeding islands. Average lifespan is 15 to 24 years with the young reaching sexual maturity at about four to five years. However, males will generally fail to hold a territory until they are older (2).

The California sea lion is currently classified as Lower Risk / Least Concern on the IUCN Red List and at present the population is quite capable of recovering from limited conflict with humans and the occasional El Niño event. As long as there is enough food, and some level of protection remains, it is thought that there is no immediate threat to the survival of the California sea lion. The extinction of the Japanese sea lion, however, reminds us that there can be limits to the recovery of populations from high mortality, especially for the smaller population in Mexico, where human interaction combined with natural stress may make recovery more difficult (2).

This highly social and intelligent species is well adapted to a semi-aquatic life-style. California sea lions swim using their fore-flippers and are particularly agile on land as they are able to control their hind flippers independently (3). Male and female California sea lions differ significantly in appearance. Males are substantially bigger than females and have an enlarged sagittal crest, which is usually topped with white fur. The adult males are generally dark brown with a lighter belly and side colouring, whereas the females can appear more tan coloured. The pups are born with a blackish-brown coat which moults after a month and is replaced with a light brown coat. This coat is shed after four or five months and replaced with the adult coat. The California sea lions found in Mexico appear smaller than those found in California (2).

Breeding occurs on sandy beaches and rocky areas of remote islands where there is easy access to shade, water for cooling down and plenty of food (2). California sea lions generally fish in open waters along the Pacific coast, but are increasingly being found up rivers and often congregate on man-made structures such as jetties and piers (5).

Found from British Columbia in Canada south to Baja in Mexico, including the Gulf of California. California sea lions breed mainly on offshore islands from southern California's Channel Islands south to Mexico (4).

Classified as Least Concern (LC) on the IUCN Red List (1).

The California sea lion faces a number of threats, most notably through human-animal conflict and climate change. In the 19th and early 20th centuries California sea lions were extensively killed for commercial purposes, and although later afforded some protection, were still killed in large numbers until hunting was banned between 1969 and 1972. Population numbers have now recovered, but growing numbers are being killed in fishing nets. California sea lions are also increasingly thought to be damaging commercial fish stocks and in 1999 the federal National Marine Fisheries Service released a report recommending that Congress allow wildlife managers to kill California sea lions that are preying on endangered fish species (6). California sea lions are also negatively affected byEl Niño, which causes a shortage in food supply and increased mortality (2). Other causes of mortality include infection, disease, poisoning, pollution and toxic phytoplankton blooms (2) (6).