CALIFORNIA SEA LION
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Mother With Pup |
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Male |
The
California sea lion is a coastal
eared seal native to western North America. It is one of the six species of sea
lion. Its natural habitat ranges from southeast Alaska to central Mexico,
including the Gulf of California. California sea lions are sexually dimorphic;
males are larger than female, and have a thick neck, and protruding sagittal
crest. They mainly haul-out on sandy or rocky beaches, but they also frequent
manmade environment such as marinas and wharves. California sea lions feed on a
number of species of fish and squid, and are preyed on by killer whales and
great sharks.
The
California sea lion is the well- known performing “seal” of zoos, circuses, and
oceanaria. It is a sexually dimorphic species, with males reaching three to
four times the weight of adult females and 1.2 times their length. Males become
very robust in the neck, chest, and shoulders. As males become sexually mature
the sagittal crest enlarges. The crest first appears as a bump on the crown,
then grows to become a large prominent ridge, often steep in the front that
creates a tall forehead. The canine teeth of adult males are larger and thicker
than those of females.
Adult
and sub adult male California sea lions bark in often long, repeated sequences.
The bark is loud, moderate in pitch, and often delivered while the head is
waved from side to side. Females and juveniles do not produce the repetitive
bark. Juveniles and sub adults of both sex’s growl, and when alarmed produce a
loud shriek-like bark that is high pitched. The growl of adults is
low-frequency and roar-like, and can be explosive, when the animal is angered
or startled.
Both
sexes have a long and somewhat narrow muzzle that tapers to a blunt nose. In
profile, the face of younger animals is dog-like. Adult females and juveniles
do not have a sagittal crest, and in profile have a flat head that smoothly
transitions into the muzzle with a slight drop. In contrast to adult males,
adult females have a long, relatively thick neck and a wide body behind the
fore flippers.
The
fore flippers have a sparse short fur that extends beyond the wrist onto the
middle of the dorsal surface of the flipper in a “V” pattern that does not
reach the round tip. The rest of the dorsal surface, and the palms of both fore
flippers are covered with a hairless black leathery skin. There is a small
opening in the skin at the end of each digit for a claw that is usually reduced
to a vestigial nodule, and rarely emerges above the skin. The claw openings are
set back from the free edge of the flippers by cartilaginous rods that extend
the length of each digit, and expand the size of the flippers. The hind
flippers also have cartilaginous rods that extend the length of each toe. The
bones of the three central toes terminate at the position of the small nails
that emerge through the skin on the dorsal surface, set back from the end of
the flippers. The first and fifth toes are longer than the three middle toes,
and the first toe, or hallux, is longer and wider than the fifth toe. The hind
flippers have short hair covering part of the proximal end of the flipper; the
rest of the dorsal surface and the entire sole is covered in black, leathery,
hairless skin.
The coloration of California sea lions is variable. When dry, the coat of most adult males is dark brown, and when wet they appear blackish. Males being to darken as sub adults, and complete this change when they reach physical maturity. However, some males do not darken completely or even extensively, and remain various shades of tan to light brown on the sides, belly, and rear quarters. Adult females are tan above, and various shades of tan to light brown below. They are usually the same colour on the underside of the neck as on the back, and somewhat darker, on the rest of the ventrum and around the base of the flippers. Adult and large sub adult males are light-coloured on the muzzle, around and above the eyes, on the ear pinnae, and on the sagittal crest. Coloration of juveniles and young sub adult males is similar to adult females. Pups are born with a thick brownish-black lanugo that is generally molted by the end of the first month. The succeeding light brown juvenile coat is shed 4-5 months later, and is replaced by adult coloration. California sea lions appear duller and greyer as they get close to the time of the annual molt. The dental formula is I3/2, C1/1, PC5/5 (~79%), and PC 6/5 (~21%).
Dental Formula I3/2, C1/1, PC5/5 and PC 6/5.
Size
Male California
sea lions reach lengths of 2.4m, and weights of more than 390kg. Females only
reach 2m, and weight an average of 110kg. New born pups are about 80cm long and
6-9 kg.
Life span
Live up to 15- 20 years in the wild and Average25-30 years in human care.
Gestation
period 259 days.
Can be confused with
California
sea lions share their range with three other otariids: Steller sea lions, and
northern and Guadalupe fur seals. Juvenile, sub adult, and smaller adult female
steller sea lions fall within the size range of California sea lions. Careful
attention to head and muzzle size and shape, overall coloration, and length and
width of fore- and hind flippers permits differentiation. Smaller steller sea
lions in the size range of large California sea lions will look like they are
more muscular and powerfully built than similar- sized California sea lions,
which look more rounded and streamlined. Also, smaller steller sea lions have
no sagittal crest development and a nearly flat-topped head, whereas
comparably-sized adult and sub adult California sea lion males have a moderate
to large sagittal crest and more pronounced forehead. Steller sea lion eyes
appear smaller and set farther apart, due to the proportionately larger head
and wider muzzle.
Both
northern and Guadalupe fur seals have thick pelage and look shaggier than the
more sleek California sea lions. Males of both fur seals are dark in colour,
often with light tips to the long hairs that impart a greyish cast to the dark
colour. Adult females, juveniles and sub adults are multi-coloured with dark
grey or brown dorsal, tan to buff ventral coloration, and a pale band across
the chest. Both fur seals have a more pointed face and proportionately longer
ears that stand out farther from the head when they are in the water or
otherwise wet. Adults of both fur seals have conspicuous long, pale vibrissae.
Northern
fur seals have a very short pointed muzzle, very long hind flippers with long
cartilaginous extensions all of equal length and width. The fur on the dorsal
surface of the fore flippers stops abruptly at the wrist line, or bend point,
and the top of the flippers has a smooth “clean shaven look”. This is in
contrast to the California sea lion, which has fur on the top of the flipper
extending in a “V” beyond the wrist.
Guadalupe
fur seals have a long, pointed muzzle. The somewhat bulbous nose contributes to
an upturned silhouette of the muzzle. The hind flippers are longer than those
on California sea lions, but lack the extreme length of northern fur seal hind
flippers. The fore flippers have short hair extending in a “V” beyond the wrist
line on the dorsal surface.
Distribution
The
California sea lion occurs in the eastern north pacific from the Tres Marias
islands north of Puerto Vallarta, Mexico, north throughout the gulf of California,
and around the end of the Baja California peninsula north to the gulf of
Alaska. Vagrants have been reported from the Bering Sea in the north to
Acapulco in the south. Most rookeries are south of point conception, southern
California. Many islands free of predators and sources of human disturbance
throughout their range are used as haul outs. The California sea lion
population is currently expanding, and is extending its breeding range
northward. Females, which were only very rarely found north of point conception
in the early 1980s, are now routinely found in northern California, where
former breeding sites have been reoccupied. They are now occasionally found in
Alaska, in the northern part of the species range.
California sea lions are usually found in waters over the continental shelf and slope, however, they occupy several landfalls far offshore in deep oceanic areas, such as Guadalupe Island and Alijos rocks off Baja California. Large numbers of adult and sub adult males and juveniles undertake a post-breeding season migration north from the major rookeries in southern and Baja California and winter from central California to Washington State. Smaller numbers of animals migrate to British Columbia and southeast Alaska, making it to the northern Gulf of Alaska coast. California sea lions occupy the Gulf of California year round. Those residing there do not appear to make long migrations. Throughout their range, California sea lions frequent coastal areas including bays, harbors, and river mouths, and regularly haul-out on buoys, jetties, boat docks, and even on anchored boats. They traditionally haul-out on certain coastal headlands and under cliffs that limit access and approach by terrestrial predators.
Ecology and behavior
Pupping and breeding take place from May
through July. Males are highly polygynous and hold territories both on land and
in shallow water near shore for periods up to 45 days. Females stay ashore with
their newborn pups for about 7 days before they depart for first of many
foraging trips that usually last 2-3 days and are followed by attendance of the
pup at the rookery for 1-2 days. Most pups are weaned at 10 months, but long
before this, they start making foraging trips to sea with their mothers. Some
pups continue to receive care as yearlings, and even as 2- years-olds. Estrus
occurs around 27 days after giving birth. California sea lion females often
gather in “milling groups”, where they roll in the surf and sand, mounting each
other and even nearby bulls. Often the females from the milling group disperse
after one or more of them copulates with a bull.During breeding season they are referred to as a rookery
and when several females are in one male territory, they are called a harem.
The
diving pattern of lactating adult females is consistent with a number of other
otariid species. The deepest dive recorded to date was to approximately 274m and
the longest dive lasted just under 10 minutes. Typical feeding dives are
shallower than 80m, and last less than three minutes. Lactating adult females
are active for most of the time they are at sea and feeding bouts occur during
the day and at night, with peaks of activity at dawn and dusk. Feeding dives
occur in bouts suggesting sea lions are frequently exploiting patches of prey.
They are not known for deep or long dives.
California
sea lions will “Porpoise”, or leap clear of the water when traveling rapidly at
sea. Large, “porpoising” groups of sea lions can resemble a heard of dolphins.
Juveniles and sub adults may perform acrobatic and high vertical leaps, and
individuals of all ages surf breaking waves and sometimes ride in the stern
wakes of vessels. They are often seen at sea, rafting at the surface, alone or
in groups. Animals in rafts frequently raise one or more of their flippers high
out of water, sometimes suggesting a tall slender shark fin at the surface.
California sea lions will also float and sleep at the surface, far offshore in
rafts of kelp. They are known to travel with several dolphin species and are
thought to use dolphins to help them locate food. They will also swim alongside
large cetaceans, such as blue and humpback whales and ride their bow waves.
California
sea lions haul-out and travel at sea with steller sea lions, where the two
species co-occur. They will also haul-out near Guadalupe and northern fur seals
and elephant seals, and in a few locations, harbour seals.
Predation
Predators of California sea lions include killer whales, sharks, coyotes and feral dogs, and until they were extirpated from the California channels Islands, bald eagles were known to take young pups.
Feeding and prey
California sea lions are opportunistic and feed on a wide variety of prey, often taking what is abundant locally or seasonally in the areas they occupy. Principal prey taken in the pacific includes: pacific whiting, market squid, red octopus, jack and pacific mackerel, blacksmith, juveniles of various species of rockfish, herring, northern anchovy, and salmon. Sea lions in the Gulf of California have northern anchovy, pacific whiting and rockfish as prey in common with animals in the pacific, and also take various species of midshipmen, myctophids, and bass, as well as sardines, cutlass fish, alopus, and cusk eels. Because of their boldness and taste for commercially- important fish species, such as salmon and rockfish that are easily taken from fishing lines, they are considered a nuisance by many sport and commercial fishermen. California sea lions will also ascend rivers following spawning runs of anadromous fish, and take advantage of man-made structures, such as canal locks and fish ladders that concentrate prey.
Exploitation
Currently, there is no significant direct catch of California sea lions. Many sea lions, however, are shot by fishermen and certainly many others are taken incidentally during fishing operations. Set and drift gillnets, in particular, appear to be taking large numbers each year. The total population of the California sea lion in 1989 was estimated to be 160 000 and increasing, about equally split between Mexico and the United States. The number of Galapagos sea lions are unknown. Unfortunately, the Japanese race of this sea lion is now extinct.
Threats and status
California
sea lions are abundant and the population is growing. They were historically
important to native people living in coastal areas and on Islands. Numerous
kitchen middens in southern California and on the Channel Islands that contain
large numbers of California sea lion and other pinniped bones, attesting to the
importance of marine mammals in subsistence cultures prior to the arrival of
Europeans. In the 19th and early 20th centuries,
California sea lions were periodically harvested intensively for a variety of
products, and hunted for bounties to such an extent that the population may
have been reduced to as few as 1,500 by the end of this period. Protection that
began in the mid-20th century and solidified with the marine mammal
protection act of 1972 in the United States (and under similar measures in
Mexico) provided the impetus for recovery of the population, which now numbers
an estimated 211,000 to 241,000 animals in the US and Mexico.
California sea lion mortality occurs in conflicts with fisheries, by poaching, and through entanglement in marine debris. Sea lions also accumulate pollutants through the food chain, and large amounts of DDT and PCBs discharged in the past continue to accumulate in coastal marine food chains, as evidenced in part by the burdens many marine mammals carry in their tissues and organs. Large amounts of agricultural and urban runoff and waste continue to be discharged into coastal marine habitats annually from numerous sources, and this pollution is having as-yet poorly-known effects on sea lions also die from periodic outbreaks of planktonic organisms that cause paralytic shellfish poisoning. Prey availability is greatly reduced during EI Nino events, and large numbers of pups born during these periods die of starvation, as do weaker animals from all age classes.
Factors hypothesized include
The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.
IUCN Status Least concern
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