California sea lion - Zalophus californianus

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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 and are proportionately smaller in the abdomen. As males become sexually mature they begin to develop an enlarged sagittal crest. The crest first appears as a bump on the crown that 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 subadult male California sea lions bark in often long, repeated sequences. The bark is loud, moderate in pitch, and often delivered while the head is waving from side to side. Females and juveniles do not produce the repetitive bark. Juveniles and subadults of both sexes growl, and when alarmed produce an explosive 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 thin 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 rounded tip. The rest of the dorsal surface, and the palms of both fore flippers are covered with a hairless black leathery skin. The first digit is the longest, widest and thickest, and curves posteriorly, giving the flipper a swept back look. Digits 2–4 are successively shorter. 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 flipper. 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, and the rest of the dorsal surface, and the entire sole is covered in black leathery hairless skin.

Color of California sea lions is highly variable. When dry, the coat of most adult males is dark brown, and when wet they appear blackish. Darkening begins when males are subadults and is generally complete when a bull reaches physical maturity. However, some males do not darken completely or even extensively, and are various shades from tan to dark or rusty brown on the sides, belly, and rear quarters. Adult females are pale colored above, and can be various shades of tan to light brown. They are usually the same color on the underside of the neck as on the back, and can be somewhat darker around the insertion of the flippers, and ventrally on the abdomen and lower chest. There are often light colored areas on the muzzle, around and especially above the eyes, and on the ear pinnae, which highlight these areas. The sparse short fur covering a portion of the tops of the flippers can be the same color as the body or darker. Coloration of juveniles and young subadult 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 grayer as they get close to the time of the annual molt.

Male California sea lions reach lengths of 2.4 m, and weights of more than 390 kg. Females only reach 2 m, and weigh an average of 110 kg. Newborn pups are about 80 cm long and 6–9 kg.

The dental formula is I 3/2, C 1/1, PC 5/5 (~79%), PC 6/5 (~21%).

California sea lions share their range with three other otariids: Steller sea lions, and northern and Guadalupe fur seals. Juvenile, subadult, and small 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 filled-out with fat and streamlined. Also, smaller Steller sea lions have little or no sagittal crest development and a nearly flat-topped head, whereas comparably-sized adult and subadult California sea lion males have a moderate to large sagittal crest and more pronounced forehead. Steller sea lion eyes also seem 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 lion. Males of both fur seals are dark in color, often with light tips to the long hairs that impart a grayish cast to the dark color. Adult females, juveniles and subadults are multicolored with dark gray 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 long white conspicuous vibrissae.

Northern fur seals have a very short pointed muzzle, very long rear 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 in the flipper, and when wet the flipper has a smooth ‘clean shaven look,’ 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 that is slightly upturned at the end. The nasal tissue is somewhat bulbous contributing to the upturned silhouette of the muzzle. The rear flippers are longer than those on California sea lions but lack the extreme length of northern fur seal rear flippers. The fore flippers have short hair beyond the wrist line on the dorsal surface.

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 the 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 are making foraging trips to sea with their mothers, presumably learning by observation where and when to search for food and how to catch prey. Some pups continue to receive care as yearlings and 2–year olds. Female estrous occurs around 27 days after giving birth, and groups of milling females gather in the surf where the females roll in the water and on the sand, and mount each other and the bull until one or more of them copulates with the male, at which time the group often disperses.

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 274 m and the longest dive lasted just under ten minutes. Typical feeding dives are shallower than 80 m, 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.

California sea lions are fast maneuverable swimmers, but are not known for deep or long dives. They will ‘porpoise,’ or leap clear of the water when traveling rapidly at sea, sometimes traveling like this in large groups. Juveniles and subadults may perform acrobatic and high vertical leaps, and individuals of all ages surf breaking waves and sometimes ride in the stern wakes of vessels. When resting at sea, they can be seen rafting at the surface alone or in groups. Animals in rafts frequently raise one or more of their flippers high out of the water, sometimes suggesting a tall slender shark fin at the surface. California sea lions will also float and sleep at the surface within free floating detached rafts of kelp or ‘kelp patties.’ California sea lions will travel with several dolphin species and will swim alongside large cetaceans, such as blue and humpback whales.

California sea lions will haul–out and travel at sea with Steller sea lions wherever the two species co–occur. They will also haul–out near Guadalupe and northern fur seals and elephant seals, and in a few locations, harbor seals. California sea lions will haul–out on buoys, and on boats at anchor or even on boat docks in marinas. Once established, these sites are regularly used and the numbers of animals will expand if space permits. Predators of California sea lions include killer whales, sharks, coyotes and feral dogs, and until they were recently extirpated from the California Channel Islands, bald eagles were known to take young pups.

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. A lower diversity of prey is taken outside the breeding season, when many animals disperse over large areas, as opposed to during the breeding season, when preferred prey can be reduced by intense foraging activity in small areas within traveling range of the rookeries. Principle prey taken by California sea lions 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, cutlassfish, 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, California sea lions 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.

California sea lions are abundant and the population is growing. They were historically important to native people living in coastal areas and on islands used by sea lions for rookeries. Huge middens in southern California and on the Channel Islands, with large numbers of California sea lion and other pinniped bones, attest to the past importance of marine mammals in subsistence cultures prior to the changes that followed the arrival of Europeans on the west coast of North America. In the 19th and early 20&supth; 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 United States 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 lion immune systems and overall health. California sea lions also die from periodic outbreaks of planktonic organisms that cause paralytic shellfish poisoning. Prey availability is greatly reduced during El Niño events, and large numbers of pups born during these periods die of starvation, as do weaker animals from all age classes.

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Antonelis, G.A., Jr., C.H. Fiscus and R.L. Delong. 1984. Spring and summer prey of California sea lions, Zalophus californianus, at San Miguel Island, California, 1978-79. Fisheries Bulletin 82(1):67-76.

Aurioles, G.D. and G.A. Zavala. 1994. Ecological factors that determine distributions and abundance of the California sea lion Zalophus californianus in the Gulf of California. Ciencias Marinas 20(4):535-553.

Feldkamp, S.D., R.L. Delong and G.A. Antonelis. 1989. Diving patterns of California sea lions, Zalophus californianus. Canadian Journal of Zoology 67:872-883.

Francis, J.M. and C.B. Heath. 1991. Population abundance, pup mortality, and copulation frequency in the California sea lion in relation to the 1983 El Niño. pp. 119-128 in F. Trillmich and K.A. Ono, eds. Pinnipeds and El Niño: Responses to environmental stress. Ecological Studies 88. Springer-Verlag, Berlin.

Heath, C.B. 2002. California, Galapagos, and Japanese sea lions Zalophus californianus, Z. wollebaeki, and Z. japonicus. pp. 180-186 in W.F. Perrin, B. Würsig, and J.G.M. Thiewissen, eds. Encyclopedia of marine mammals. Academic Press.

Melin, S.R., R.L. Delong, J.R. Thomason and G.R. Vanblaricom. 2000. Attendance patterns of California sea lion (Zalophus californianus) females and pups during the non-breeding season at San Miguel Island. Marine Mammal Science 16(1):169-185.

Odell, D.K. 1981. California sea lion – Zalophus californianus (Lesson, 1828). pp. 67-97 in S.H. Ridgway and R.J. Harrison, eds. Handbook of marine mammals, Vol. 1: The walrus, sea lions, fur seals and sea otter. Academic Press.

Peterson, R.S. and G.A. Bartholomew. 1967. Natural history and behavior of the California sea lion. American Society of Mammalogists Special Publication Number 1. Allen Press. 79 pp.