San Francisco State University
Geography 316: Biogeography
The Biogeography of California Sea Lion (Zalophus californianus)
by Breana Delight Wheeler, student in Geography 316, Fall 2001
| Kingdom: Animalia
Phylum: Chordata Class: Mammalia Order: Carnivora* Family: Otariidae Genus: Zalophus Species: Zalophus californianus *See Evolution Subspecies: |
 Figure 1. Female sea lion. Picture taken at Pier 39 San Francisco, CA |
Description of Species:
There are three subspecies of Zalophus californianus: Z. c. californianus, Z. c. wollebaeki
and Z. c. japonicus. (Martin 1977) Z. c. japonicus is generally believed to be
extinct. (Orr and Helm 1989)
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 (TMMC 2000). The flippers are long and leathery with nails
(British Columbia Adventure Network 2001). Males
are darker and larger than the females. Males
weigh between around 850 lbs. and possibly over 1,000 lbs.
They can grow up to 6 feet in length. Their
necks are quite thick (Orr and Helm 1989) and they “have a mane of longer hair on the
neck” (Ridgway 1972). Females grow to
around 220 lbs. and up to 6 feet length (TMMC 2000).
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 which can be as high as 1 ½
inches in height by the time the male is ten years old (Bonner 1994). Vocalizations are frequent and play an important
part in maintaining territorial boundaries. The
barking is also used as a signal for danger (Ridgway 1972).
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 (Martin 1994). The mating season, which occurs from May to July,
affects the appetites of the adult animals, the males in particular. This appetite loss occurs in individuals in
captivity as well (Ridgway 1972).
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 (Orr and Helm 1989) 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. (CERES 2001)
Males will mate with an average of 16 females in one season. The female actively solicits a male to copulate with her and she actively terminates copulation. (RWPZ 2000) The bulls patrol territory ferociously and defend their harems of up to forty cows. (Martin 1977) 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. (RWPZ 2000) 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. (DRC 2001)
Cows of Z. c. californianus and Z.
c. japonicus give birth in May and June. The Galapagos sea lion gives birth at the end
of year because of the equatorial location of their habitat. 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 (Ridgway 1972).
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." (DRC 2001)
The California sea lion is flourishing. Population
figures for the California sea lion are estimated at between 50,000 and 150,000
individuals for Z. c. californianus and that they are growing at an annual rate of
up to five percent (Orr and Helm 1989 and Martin 1994 respectively) and around 25,000 of Z.
c. wollebaeki (Orr and Helm 1989).
In the early 1800s, the California sea
lion was hunted extensively, mostly for the oil from their blubber, which had various
uses. One barrel of this oil was made from
the blubber of three sea lions (Martin 1977). Commercial
fishermen and the 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 will put pressure on the total population (Orr and Helm 1989).
Evolution:
There are many debates in the scientific
community about the classification of all species described in the world. For the California sea lion, there is a debate on
whether it should be classified under the Order Carnivora as it always has been or if it
should be given its own rightful Order Pinnepedia. Martin
(1977) refers to Pinnepedia but a later reference by Bonner (1994) keeps them in the
Carnivora order. Many refer to Pinnipedia as
a suborder. The California sea lion is a
descendent of “bear-like” carnivores and dogs. (Bonner 1994) They originated on land but entered the sea. The earliest fossils were found in California and
were dated during the beginning of the Miocene epoch, some 22.5 million years ago. Atkins (1999) concurs with this time line.
Figure 2. Evolution of Zalophus genus,
based on assumption of Carnivora as correct Order classification.
Classification of Zalophus is still under debate. While some of the
literature classifies Pinnipedia as its own Order (Amador 1999), many still believe they
should be classified as Carnivora (IMMA 2001).
Distribution
Map of Distribution:
| Z. c. californianus is continuously distributed from
Vancouver Island, British Columbia (about 50° N) to the Tres Marias Islands off Mexico,
at 21° N. (Bonner 1994). There have been rare sightings in Alaska. (Orr and Helm 1989)
Males move seasonally up and down the Pacific Coast of North America, north in the winter
and south in the spring. The females usually do not venture beyond the Channel
Islands in southern California. (DRC 2001) Sea lions need to be close to land
because they must come out of the water to rest and to breed. Their food sources live
close to the shore as well. Z. c. wollebaeki lives in the Galapagos Islands. They tend to be smaller than Z. c. californianus and also stick close to land for resting areas and food sources. Z. c. japonicus, a subspecies that was found on the coast of Honshu Island, Japan, near Korea is very likely to be extinct (Bonner 1994). 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. Z. c. japonicus, a subspecies now considered extinct, once was distributed on the western side of Honshu Island near Korea. Honshu Island is the main island of Japan. |
Figure 3. Distribution in North America of Z. c. californianus |
Other interesting issues:
The Marine Mammal Protection Act of 1972-
By passing this act, Congress recognized that certain species and populations may be in
danger as a result of man's activities; these species must not be allowed to drop
below viable numbers; all efforts must be made to return these species to healthy
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. (NMFS 2001)
In the Spring 2001 issue of The Newsletter of The Marine Mammal Center, Sue Spong
reported that The Marine Mammal Center has found a high rate of cancer among California
sea lions. 18% 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 its way up the food chain to the sea lion. While the California sea
lion population is not endangered, this species could serve as a indicator species on the
overall general health of the coastal food chains.
Bibliography
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State Academy of Science. [Online].
Available: http://www.il-st-acad-sci.org/mammals/mami001.html
Atkins, David L. August 26,
1999. Chordate Biology: Mammalian Order
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Available: http://gwis2.circ.gwu.edu/~atkins/newwebpages/Mammalia/carnivora/carnivora.html#evolution
[2 November 2001]
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[12 October 2001]
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[16 October 2001]
San Antonio Zoo. Date Unknown. "California Sea Lion". [Online].
Available: http://www.sazoo-aq.org/sealion.html [12 October 2001]
Spong, Sue. Spring 2001. "Cancer in California Sea
Lions". Release: The Newsletter of the Marine Mammal Center Vol. 21, No.
1: 1-3.
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Sea Lion. [Online].
Available: http://www.tmmc.org/csealion.htm
[12 October 2001]
University of Texas-Austin. Perry- Castaneda Map Collection. North America Reference Map 2000. [Online]. Available: http://www.lib.utexas.edu/maps/americas/northamerica.jpg [15 November 2001]
send comments to bholzman@sfsu.edu
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