Sea Lions breed and bear young in the spring, usually in May and June, although some breeding occurs as late as July or even August. The coincidence of breeding and bearing was once thought possible because female Sea Lions have a twin uterus, a characteristic of all pinnipeds. Also, it was assumed that the Stellar Sea Lion bore a pup each year like it's close relative the Alaska Fur Seal.
However, through close observation, it has been concluded that the females generally bear every other year, as half-grown pups have been seen nursing at their mother retractable dugs well past bearing time. This variation from the Otariidae family pattern may well have developed to give the young sea lions a better diet and thus a better chance of survival.
Gestation has been timed at nine months. There is apparently some system of delayed impregnation which makes bearing time conform to the mating season. Cows that lose their pups soon after birth probably breed again immediately and bear the following season.
During the breeding season, the bulls fight for territories on the rocky ledges just outside the cave. Only the largest and strongest bulls maintain harems of fifteen to thirty cows. The remainder are called bachelor bulls and are driven away to live elsewhere during this period. From April until about mid-July, the family structure is plainly evident with the young born on the rocky ledges outside the cave. It is very rare for a cow to give birth inside the grotto.
Until late in July when the harem structure dissolves, the herd bulls keep constant vigil over their females. Occasionally a young, strong bachelor succeeds in besting an older bull thereby acquiring the herd. The herd bulls do not leave their harems even for food for perhaps three months. Only the largest ocean waves can drive them from the ledge into the sea. Females display no loyalty and when a harem is broken by a storm, the bull may never recover all of his chosen mates. Therefore, much of his work involves keeping his "wives" from slipping away in search of food or because of high waves and rough ocean. Naturally, the bulls have lost weight and are exhausted by the end of the breeding season and they generally spend the remainder of the summer by themselves, resting and regaining their strength.
The variety of sea lions which live at Sea Lion Caves is commonly called the Northern, or Steller, sea lion. This sea lion is named after George Wilhelm Steller, an eminent German naturalist who accompanied the Danish explorer Vitus Bering in 1741 on his second Alaskan expedition. Steller was the first qualified observer to study and classify these animals.
The Steller sea lion is a member of the Otariidae family, or eared seal. It is characterized by an external ear which can be closed when entering water and by hind feet or flippers that point forward. In contrast, Phocidae, or true seal, has no external ears and it's rear flippers point backward. Also belonging to the Otariidae family is the California sea lion and the Alaska fur seal.
The Alaska fur seal (Callorhinus alascanus), is not found at Sea Lion Caves. The California sea lion (Zalophus californianus) is seen all along the Pacific Coast and is generally found at Sea Lion Caves from late fall to early spring. It readily adapts to captivity and is trained for circus acts.
The largest of the eared seal family and the principal tenant of Sea Lion Caves is the Steller sea lion. This animal is also considered non-migratory because there is no mass movement to summer or winter grounds, although individuals or small groups may travel hundreds of miles in search of food. It is found from the central California coast, north to the Bering Sea and back south into northern Japanese waters. A recent U.S. Fish and Wildlife Survey indicates a possible total population of nearly 80,000 Steller sea lions. Most of these animals live on the offshore islands and rocks of British Columbia and Alaska. Some Stellers live along the California coast and about one thousand reside in Oregon Waters. The number of Steller sea lions in the Sea Lion Caves area varies from season to season and from year to year with the herd averaging about 200 animals.
Sea Lions are mammals, or warm blooded animals which give birth, nurse their offspring, and must breathe air. Sea Lions are a lso pinnipeds - literally, feather-footed - meaning they have finlike members for propulsion. Their pelvic bone structure allows independent use of their flippers, and therefore, they can walk on their four weblike flippers which contain the same bony structure as the legs of land animals. In the water, the Steller sea lion swims by using a breast stroke and may reach a top speed of about 17 m.p.h. In contrast, other marine animals, such as the whale, depend on fishlike body action to move through the water. The true fur seal folds its front flippers and swims by the force of its trailing rear flippers.
Young sea lions called pups seem to be immune to most diseases as long as they are breast fed. As they mature, pups become susceptible to internal parasites such as round worms and tape worms which are a deterrent to both growth and longevity. Population increases are also somewhat checked by adult sea lions inadvertently trampling their young and also by accidental drownings of the newly born which have not yet learned to swim.
Sea lions are carnivorous. Their skulls are similar to those of bears and their jaws contain sharp teeth much like those found in dogs, cats, and other flesh eaters. They feed exclusively on fish they catch themselves; their diet varying with whatever is abundant in the area. In the vicinity of Sea Lion Caves, they appear to subsist chiefly on bottom fish such as skate, small sharks, squid and various species of rock fish. Sea lions may descend in search of food to a depth of 80 to 100 fathoms, and normally remain submerged no longer then four or five minutes.
Possible sea lion predation on commercially valuable fish has been of some concern. Because of the animal's remote and rugged habitat, and because collecting specimens at sea is difficult, much is unknown about its diet habits. However, recent scientific studies indicate that valuable fish such as salmon constitute a very minute part of the sea lion diet. Although sea lions are good swimmers, they find it much easier to capture more sluggish victims than game fish.
If provoked, the Steller sea lion would not deliberately attack a human; however, a descent by man into the midst of a harm during the mating season would be foolish. Precautions are taken at Sea Lion Caves to prevent this from happening.
Sea lions pups are about four feet long at birth and weigh from 40 to 50 pounds. They are slate gray in color for about six months, turn dark brown until approximately two years of age, and they begin to assume the lighter tan color of the adult. They remain with their mothers well over a year and grow rapidly, averaging about six feet long at the end of their first year. The pups continue to grow, perhaps all of their lives, but the growth rate decreases each year. Mature cows are identifiable by their size and long slender shape. They average about eight or nine feet in length and weigh from six to seven hundred pounds. The bulls are much larger and have massive shoulders. They average twelve feet in length and weigh around 1500 pounds. Many extremely large bulls have been known to weigh well over a ton. The average life span of these animals is believed to be about 20 years.
The Steller sea lion has no fur, but instead is covered with a course, short hair about one inch long on its body, and the mature bull has slightly longer hair resembling a mane around his neck. Therefore, the Steller is of no commercial value except that some natives in remote northern parts of Alaska occasionally take the animal for food or for the skin which is used in boat making.
For some reason, experts have found that the stomachs of many adult sea lions contain stones! These stones very in number and size from pebbles to three inches in diameter. No one knows whether the stones serve some useful function to the sea lion or whether they might have been swallowed accidentally, possibly in play.