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The Sea Otter & Climate Change

Breakfast with a sea otter; Seward, Alaska

The sea otter is the largest of the weasel family; it is also the smallest marine mammal. Adult males average five feet in length and ninety pounds. Females are about the same length, but run about thirty pounds lighter.

Life span is between 15-20 years in the wild. Sexual maturity happens at 2-3 years for females, and 4-5 years for males. It should be noted, it may take several more years for a male to breed, until one holds a breeding territory. Breeding can happen at any time of the year, and young can be born during any and all seasons, but in Alaska, birth usually occurs in the spring. The female raises one pup per year.

In order to maintain body weight, a sea otter must eat 25% of its mass, every day. They have the densest fur of any mammal, with between 800,000 – 1 million hairs per square inch.

Sea otter range in Alaska

Alaska has three distinct populations of sea otter: The Southwest, South-central and Southeast. Alaska is home to 90% of the world sea otter population.

The Southeast and Southcentral population is stable, but the Southwestern population has been listed as threatened since 2005. This population, which runs from Kodiak Island west throughout the Aleutian Chain, has lost roughly 65% of its numbers since the 1980’s.

Kelp forest in the Aleutian Islands; Photo credit: UAF

Sea otters are considered a keystone species in the Alaska coastal environment. Now, they are proving to be the protectors of the underwater kelp forests. As the sea otter population plummeted in the Aleutians, the sea urchin population exploded. The sea otter is the number one predator of the sea urchin; sea otters will eat them like popcorn.

Sea urchins along an Aleutian reef, no kelp forest; Photo credit: UAF

The number one predator of the kelp forest, is the sea urchin. Without the sea otters to keep the sea urchin population under control, the urchins have decimated the kelp forest along the Aleutian Chain. Now, the sea urchins are destroying the reefs along the Chain. With the drop in kelp, the sea urchins are eating the algae that creates the reef. These reefs are disappearing right before researchers eyes.

The kelp forest are now gone from the central and western Aleutians. In their place are often 400 sea urchins per square meter. The loss of the kelp is huge on several fronts. It is a home and safety zone to numerous fish species, cod among them. The 1200 mile Aleutian Chain supports two multi-million dollar fisheries: Bristol Bay and the Bering Sea.

Kelp is also an extremely efficient absorber and holder of CO2. Like all land plants, kelp forests take CO2 out of the air during photosynthesis. Without kelp, the oceans lose a tool in lowering carbon in the atmosphere. Kelp forests also help reduce the force of storm surges, which Alaska is facing more and more.

According to the Alaska Department of Fish & Game, there are several potential drivers for the western sea otter population drop. Overharvest, disease and predation. The new predator on the block in the Aleutians is the killer whale. Prior to 1991, there was not a documented case of an orca singling out sea otters for a food source. Now, it seems to be common. What changed? Something else changed in the diet of orcas that now makes the sea otter worthwhile. There are several theories, but no definitive answer.

Currently, sea otters are protected under the Marine Mammal Protection Act.

Sources: University of Alaska – Fairbanks; Alaska Department of Fish & Game; Fairbanks Daily-News Miner; Alaska SeaLife Center; Ocean Conservancy.