Our Ocean Backyard
By Dan Haifley
Dan Haifley, Our Ocean Backyard: Defending Twin Lakes beaches in World War II
According to Dr. Tim Tinker, a UCSC adjunct professor and USGS biologist, the 2,944 southern sea otters that live in California’s near-shore waters do sleep. They slumber eight to 10 hours a day but unlike humans, they spread it out to about four to six rest periods in 24 hours. During their waking hours they feed but also groom, travel and interact with other otters.
By managing their waking activity through the day, otters are better able to maintain their body temperature. They eat as much at night as they do during the day.
The time they spend feeding depends on the abundance of their preferred prey. Tinker says that in areas such as Monterey where sea otters are at high density and there’s more competition for food, they can spend more than 40 percent of their time feeding. But in areas such as Santa Barbara, where they are still at low densities and preferred prey is abundant, otters may only feed 30 percent of the time, or seven hours a day.
Female sea otters can give birth at age three, and can bear pups for the rest of their adult lives, typically 12 to 16 years.
Pups can be born at any time of year, although more tend to be born in fall or early spring, and are dependent on their mothers for six months. After they are weaned, their mother mates again and, after a six-month pregnancy, raises another pup.
Male otters establish a territory at age 5 to 7, Tinker said. That area consists of a quarter mile of coast or less, from which other adult males are excluded.
Not all males are territorial. Some congregate in male-dominated areas, particularly at the north and south ends of the range, and also in some sand-bottom areas such as in Monterey Bay where there is little or no kelp.
Reproduction should build their population if the mortality rate isn’t too high, says Tinker, who said he doesn’t believe that reduced genetic diversity resulting from their reduced numbers in the early 1900s is limiting population recovery. “The rate of reproduction for southern sea otters is identical to that seen in related northern populations, and their rate of range expansion is also very similar to that in northern populations, although due to the nature of (the narrow) coastal habitat in California, they are restricted to expanding either north or south,” Tinker said.
The stalled population growth, according to USGS’s latest report, appears to be mostly due to the increased number of deaths from shark bites at the northern and southern ends of the range.
In the center of the range, there are fewer shark bites. This is where the population is at equilibrium with available food resources, so the numbers are unlikely to increase much more. “Basically, further recovery will require further range expansion and growth of the population at the ends of the range,” Tinker said.
My next column: Moving south, building kelp beds?
Dan Haifley is executive director of O’Neill Sea Odyssey. He can be reached at firstname.lastname@example.org.