Sea Lion Caves News

Sea Lion Count Reveals Pup-ulation Boom Off Coast

posted on 02-21-1978

The West Coast has more seals and sea lions than was thought.

Earlier estimates were based on observations t only a few places. The new figures come from a comprehensive count made by Bruce Mate, Oregon State University oceanographer and international authority on marine mammals. Findings will also provide valuable management guidelines for the future.

In a small rented plane, Mate flew the full length of the West Coast 11 times (from upper Canada to central Mexico), taking pictures monthly of seals and sea lions along the shore line and on offshore islands. This work took 1,100 hours of flying time, covered 90,000 miles, and produced 12,000 photos and slides from which seal-sea lion counts were made.

The study, started in 1974, produced these findings:
1. The harbor seal population was counted at 12,000. This is three times the total that had been projected from earlier estimates and counts made at only a few sites along the coast.
2. The count of 88,000 California sea lions was twice previous estimates. Big seasonal differences in numbers were noted at various sites. Largest numbers were counted during the breeding season (June and July) in southern California and Mexico, when mature animals are found ashore. During the non-breeding season, males undertake an unexplained northward migration all the way up into Canada.
3. The northern (or Steller) sea lion count was just over 5,000. This is similar to historical estimates, but the southern extent of the species range is shrinking to the north.

All three mammals are found along the Oregon Coast, Mate noted.

The northern sea lion breeds along the Oregon Coast. It is seen at the Sea Lions Cave and from state parks, particularly a Cape Arago, near Coos Bay, in the late spring and through the summer. Larger numbers are found in Alaska, where a quarter of a million are estimated to live.

The harbor seal also breed off Oregon but can be more elusive, says Mate. It can be found in most estuaries and on many offshore rocks. The animals seem to be getting more numerous in the Columbia River and some other Oregon rivers. They can be seen at low tide in Tillamook, Netarts, Siletz, Alsea, Winchester and Coos bays as well as the Columbia and Rogue Rivers.

The California sea lions come to Oregon in the fall and winter from their June-July breeding spots in southern California and Baja, Mexico. Smallest of the sea lions, it is known for its bark and for its talent as a trained circus and carnival animal.

The first-ever comprehensive census of this species by Mate also showed some changes taking place in the distribution of the seals and sea lions. The Steller sea lion population, for example, was found not to be breeding in some of its historic southern areas. The reason is unknown, but may be related to competition from California sea lions, says Mate.

Interactions of the species have also been spelled out better than ever before by the study, the scientist added.

"Seals and sea lions mix much of the year but stay in separate, discrete colonies at mating times," Mate observed. All are members of the family known scientifically as pinnipeds. Walruses are also pinnipeds, but are not found in the OSU research area.

"There's an easy way to tell seals from sea lions," says Mate. "Sea Lions walk on all four flippers and have external ears. Seals drag their hind flippers on land and are without external ears."

Despite widespread interest in seals and sea lions, "very few studies have been made on entire species populations and migrations," it was noted.

Mate ranks as one of leading researchers in the world on marine mammals, having published extensively on the subject.

"All seals and sea lions have one pup a year," he continued. "Twins are very rare. Seals can give birth in water. Their pups are instant swimmers. Sea lion babies doesn't know how to swim very well at birth, however, and stay close to mother for quite a while. They may suckle for periods up to one year."

The largest of the pinnipeds is the elephant seal. Some have been reported to be as long as 22 feet and to weigh more than two tons. They are concentrated from San Francisco to the middle of Baja, Mexico. Mate?s special study ?found? them in some places where they had not been reported before, including some new breeding areas. ?It was the first time some areas had been looked at in a serious, scientific way,? he stated.

An official count of elephant seals was not announced because ?the circumstances under which we surveyed that area didn?t provide a meaningful figure,? Mate said. The numbers are estimated in the 30,000-65,000 range.

Elephant seals almost became extinct during the late 1800?s, Mate said. Because they do not flee when approached by man, whalers hunted elephant seals for their high grade and yield of oil. Now the elephant seals and other marine mammals are protected by the Marine Protection Act in the U.S. and by Mexican laws.

Mate?s research was supported by the national Marine Mammal Commission, established in 1972, to encourage research on marine mammals and to develop wise management programs, and by the Marine Mammal Division of the National Marine Fisheries Service.

In his combined role as scientist-pilot-photographer, Mate also made some ?opportunistic observations? of whales, porpoises and dolphins, which make up the ocean family called cetaceans. ?But there hasn?t been time to put that information together yet,? he said.

The seal-sea lion count was made in ?painstaking fashion,? he observed. The photos and slides were mostly taken of breeding ?rookeries? and ?hauling? areas, place where seals and sea lions rest out of the water.

The photos-slides were then projected onto a screen and the marine mammals counted one by one after each months flight. Robin Brown, a master?s degree candidate in oceanography, assisted in this phase of the project.

Mate soon found that to avoid disturbing and scattering the seals-sea lions, the plane had ?to come in flat? without making turns or dives increase motor noise. He flew at heights of 500-800 feet. Plane speeds of about 90 miles an hours allowed him to take a sequence of photos out of the open window.


?It?s the only way an accurate count can be made over a large area in a short time,? Mate stated.

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