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Threats
Rapidly declining
numbers -- cause
uncertain
STATUS:
ESA -- THREATENED
IUCN -- ENDANGERED
SIZE:
Weight:
550-2200 pounds (250-1000 kg)
Length:
8-10 feet (2.4-3.1 m)
HABITAT:
Coastal waters near
rocky islands
POPULATION:
116,000 worldwide
(1989 figure)
CURRENT RANGE:
Aleutian Islands and
Gulf of Alaska;
high latitudes of North Pacific and Bering Sea,
from California to Japan
CONSERVATION:
Critical habitat designated
in Alaska
Sea lions like to hunt in relatively shallow waters -- up to about 650 feet
(200 m) deep -- where they can feed on fish, octopus, and crustaceans. Seals and sea lions are also capable of making extraordinarily deep dives, going straight down for 20 minutes or more, then rapidly surfacing with no ill effects.
Genetic samples taken from the blood of a group of animals can reveal how many different ancestral lines have contributed
to the animals' genetic makeup. If there is little genetic variation, then these animals have descended from a limited number of ancestors, which implies that the population must have been quite small
in the past. If there is
a great deal of genetic variation, then they've had lots of different ancestors,
and have come from a once plentiful population.
In 1972, the Marine Mammal Act prohibited the taking of sea lions
in U.S. territorial waters.
Sea lions can rotate their hindfeet forward; seals (specifically phocid seals) cannot.
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The Incredible Ritual
of the Rookery
The rocky, fog-bound Aleutian Islands stretch for more than a thousand miles (1,600 km) from the southwestern coast of Alaska. They are one of the principal gathering places of Steller's sea lions, the largest of the eared seals (fur seals). Every spring, Steller's sea lions come to the islands and form huge groups known as rookeries. This gathering is at the core of sea lion life and is one of the mammal world's truly amazing rituals.
The adult males arrive first. These are big bulls, 10 feet (3 m) long, weighing a ton or more. They haul out onto beaches and stake out their individual territories -- rocky strips that they defend against other males in ritualized displays with barks, and occasional fighting. This is their springtime obsession. For two months, they don't even eat! They devote themselves completely to territorial defense and to mating with females that pass through their selected strips of beach. The largest males are usually the most successful in securing and holding on to territory, making them the likeliest to breed. A male may mate with up to 30 females, but the physiological price is steep. The stress of defending territory and mating is so great that few males can keep their place in the rookery breeding ritual for more than three or four years.
The females arrive at the rookeries shortly after the males. Within two or three days they give birth to their pups. Two weeks later, the females go into heat. This remarkable transition allows the sea lions to combine two of life's most essential activities -- giving birth and mating -- into one brief season.
Mysterious Decline
Steller's sea lions are suffering massive, inexplicable population losses. In the Gulf of Alaska and central Aleutian Islands 140,000 animals were counted in
the late 1950s. By 1965, this figure had shrunk to 68,000 -- a drop of more than 50 percent. Sea lion populations in other areas all around the world are suffering similar losses.
Could this be part of a repeating cycle? Perhaps sea lions have experienced dramatic population fluctuations throughout their evolutionary history. Scientists have explored this possibility, using genetic evidence, but have found no indication that this has occurred.
Disease is another possibility -- but no diseases have been recorded among any sea lion populations that would account for such a steep decline. Are they running out of food? Commercial fisheries have made significant inroads into the numbers of fish that sea lions eat -- but probably not enough to cause a drop of this size. pollution? Natural predators? Residual effects of the harvesting of sea lion pups in earlier times? To date, none of these potential causes can be conclusively identified as the reason for the decline in the sea lion population. Certainly there have been major changes in many aspects of sea lions' environments, but we simply don't know why they are disappearing so fast. |
