California Sea Lion
Description
of Species:
 California sea lions have long torpedo shaped bodies covered in short coarse
hair. They are distinguishable from seals because they have external ear
flaps. Sea lions have flippers that are used both for swimming and
mobility on land. The flippers are long and leathery with nails. Males are darker and larger than the females. Males weigh between
around 850 lbs. to possibly over 1,000 lbs. They can grow up to six
feet in length. Their necks are quite thick and they “have a mane of
longer hair on the neck”. Females grow to around 220 lbs. and up to
six feet in length.
Photo by Jenn Trunk
Coloring of the species ranges from a
light golden brown to a dark chocolate color. The males tend to be
dark brown, while the females are nearer to golden brown. The genus
name “Zalophus” comes from “two Greek words: za, an intensifying element and
lophos, meaning crest”. Around the fifth year, a male will develop a
high bony crest on its head that can be as high as 1 ½ inches in height by
the time the male is ten years old. Vocalizations are frequent and
play an important part in maintaining territorial boundaries. The
barking is also used as a signal for danger.
Habitat and Diet:
 California sea lions live on rocky coastline, surf and open sea. They
are partial to island habitats and rocky coastline because these areas are
isolated from the mainland and many predators. It also is the home of
their favorite types of food. California sea lions prefer squid and octopus,
but they will eat fish like hake and herring. They have also been
known to eat shellfish and even seabirds. The mating season, which
occurs from May to July, affects the appetites of the adult animals, the
males in particular.
Natural History:
The California sea lion’s breeding range extends from the Channel Islands
off southern California along the coast of Mexico to Tres Marias Islands.
Pups are born on the San Miguel and San Nicolas Islands in the Channel
Island chain. Other birthing areas are a few islands off the Pacific
Coast of Baja California. Occasionally pups are also born on Ano Nuevo
and the Farallon Islands. San Miguel Island, one of the eight Channel
Islands, is the only place in the world where five pinniped
species — California sea lions, Steller sea lions, harbor seals, northern fur
seals, and northern elephant seals — congregate and breed.
Males will mate with an average of 16 females in one season. The bulls
patrol territory ferociously and defend their harems of up to forty cows. Territorial male displays include oblique stares, head shaking, barking and
lunges toward the opponent. Such interaction between territorial males
rarely results in physical damage to either animal. Sea lions have the
ability to delay implantation by up to three months and the average
gestation period is nine months. Sea lions mate twenty to thirty days
after giving birth to their pup. There is only about one month out of
the year that a female isn't pregnant.
 A
newborn pup measures about 30 inches and weighs 13 lbs. The pup swims
on its own at two weeks and weaning is complete after five or six months. Lactation begins about two hours after the birth. The cow’s milk is 36
percent fat and 14 percent protein and lactose-free. Nursing occurs at about
two-hour intervals and lasts about ten minutes. Females return to the
sea to feed in between nursings, leaving their pups on the shore. When
they return, they identify their pups through "vocalizations and/or scent."
The California sea lion is flourishing. Population figures for the
California sea lion are estimated at between 50,000 and 150,000 individuals
and that they are growing at an annual rate of up to five percent.
In the early 1800s, the California sea lion was hunted extensively, mostly
for the oil from their blubber, which had various uses. Commercial fishermen
and fishing nets have also been a factor in California sea lion mortality
rate. Since commercial fisherman continue to overfish the oceans, the
competition between the sea lions and the fishermen is intensifying. Resources are becoming scarcer, which puts pressure on the total population.
Other interesting issues:
 Sea lions are not fully committed to the sea. They must come ashore to
rest and breed. They stick close to the shoreline where their food
sources are abundant and they can relax on a rocky beach if they are so
inclined.
The Marine Mammal Protection Act of 1972 recognized that certain species and
populations may be in danger as a result of man's activities and these
species must not be allowed to drop below viable numbers. This act also
prohibits harassment of any kind of these species. This has helped the
California sea lion population rebound in the United States.
The Spring 2001 issue of The
Newsletter of The Marine Mammal Center reported that The Center has found a
high rate of cancer among California sea lions. Eighteen percent of those examined
post-mortem were found to have cancer, most commonly in the urinary and
genital tracts. This incredibly high rate of cancer could be due to
high concentrations of PCBs and organochlorinated pesticides that run off of
land and work their way up the food chain to the sea lion. While the
California sea lion population is not endangered, this species could serve
as an indicator species on the overall general health of the coastal food
chains. Photo by Paul Riley
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