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Thursday, Jul. 02, 2009

Scientists note slight decrease in local sea otter population

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Scientists report a slight decline in the average number of sea otters living offshore of the Central Coast during the past three years.

The U.S. Geological Survey said this week that 2,654 otters were counted in the 2009 spring survey, representing a 3.8 percent drop since 2008, but just a 0.5 percent decline in a three-year average that dates to 2007.

Threatened southern sea otters, hunted by fur traders beginning in the mid-1700s, were believed to be extinct until a small population was discovered in the Big Sur region in the 1920s. Protected status allowed the population to rebound somewhat, although that seems to have leveled off.

Scientists have tracked the population through twice-a-year surveys since 1982. Population changes have ranged from an annual increase of nearly 10 percent to a decline of 3.82 percent.

USGS scientists say the latest three-year population average dipped 0.5 percent, the first time it has declined in a decade. A similar decline happened in the mid-to-late-1990s.

Scientists consider those averages to be the true measure of the population, rather than year-to-year changes. The drop in the average of counts done in 2007, 2008 and 2009 — about 13 animals — signals a slight “change in direction of the growth trend,” according to Brian Hatfield, a USGS biologist based at Piedras Blancas and who is a key survey coordinator.

“I wouldn’t really call this alarming,” he said, “but it does make you raise your eyebrow a bit and make sure you keep track of all the strandings … and wait for next spring.”

An ill or dead otter found on the shore is said to have stranded. Hatfield estimates that from 40 percent to 60 percent of otter carcasses are recovered. Although this year’s count and averages were lower, so were the number of strandings, which could belie the premise that more otters are getting sick and dying.

There are various opinions about why the counts are down, ranging from a lack of food for the otters, and the effects of pollution to the population outgrowing the “carrying capacity” of its range.

Other reasons could be illness and infections, shark attacks, bad weather impairing visibility during the counts or a shifting of the population.

For instance, Hatfield said that during this survey, some of the largest population decreases were noted at the furthest ends of the range, which stretches along 375 miles of coast between Half Moon Bay and Santa Barbara.

Local comparisons showed the population from Cayucos to Hazard Canyon was up by 64 otters this spring, but from Cayucos to San Simeon, there were 27 fewer otters.

Hatfield said stronger winds and stubborn fog made it tougher to see otters this year, particularly in areas where much of the count is done from a state Department of Fish and Game plane.

An exceptionally lush ocean-top “canopy” of giant kelp also may have made it harder to spot otters playing hide-and-seek among the fronds, where they often rest and nap.

Lab tests show some otters are dying from disease carried by parasites, viruses and bacteria found in sewage as well as urban and farm runoff.

But Hatfield isn’t ready to point a finger toward human causes as the prime reason spotters saw fewer otters this spring. “We just don’t have the hard science to prove it yet.”

The Associated Press contributed to this story.