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Puzzling story of harbor porpoises

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By Sharon Wootton
Harbor porpoises are a good example of caution about statistics, otherwise known as jumping to conclusions. Sometimes researchers have to keep plugging away at solving a puzzle, one piece at a time.
Washington’s harbor porpoises in inland waters were common in the 1940s in Puget Sound south of Admiralty Inlet. By the early 1970s, they were gone.
“They completely disappeared and no one understands why that happened,” said Joe Gaydos, director and chief scientist of the SeaDoc Society.
Theories include increasing contamination from industrial pollution, boat traffic and noise, and drowning in gill nets. Fortunately, the year-round residents have been on the comeback trail.
“The specific group of harbor porpoises that are familiar to us is distinct to inland waters and different from those off the outer coast,” Gaydos said.
“Population surveys are done every five to 10 years. The most recent survey has yet to be published, but in 2002 to 2003 there were about 10,000 porpoises of that group from the Strait of Juan de Fuca to the South Sound. A repopulated Puget Sound is a cause for celebration,” he said.
So far it’s been impossible to pin down the reason, or reasons, for the comeback, but theories include the efforts to clean up industrial pollution, the decrease in gill-net fishing, and population increasing through births.
Although the population kept rising, harbor porpoise strandings remained consistent until the mid-2000s. Then strandings increased, with 2006 numbers catching everyone’s attention.
“We determined that there wasn’t a single underlying cause. There was no common infectious disease or an episode to cause all of them to (strand),” Gaydos said.
“Last spring, there was a rash of deaths, six in the San Juan Islands and six in British Columbia, which is higher than usual for those months,” he said.
“We have really good data on how many animals we expect to strand. When the number exceeds the long-term average, that does raise a red flag, but it’s not a trend,” he said.
Gaydos is the veterinarian for the San Juan County Marine Stranding Network. He did the necropsies for the spring’s dead porpoises.
“There were some infections in the abdomen, some peritonitis, parasites in ears, and some trauma from an unidentified source,” Gaydos said.
“We’ll continue to do surveys and track the population, learn more about the life history, and where they thrive really well. They winter in the Strait of Juan de Fuca and come back inland in the springtime, so that could be why we’re seeing spring strandings,” he said.
While it’s relatively easy to track orcas because of their size (15-25 feet long), pod numbers and behavior, it’s more difficult with a smaller mammal (about 5 feet long) that avoids the limelight, travels in small numbers, and doesn’t splash.
They can dive hundreds of feet but generally swim near the surface. They breathe air, so have to come up a few times every minute, making a huffing sound as they breathe.
The Puget Sound Partnership, a state agency that coordinates various agencies, citizen groups and researchers to set priorities for a regional recovery plan, is considering the harbor porpoise as an indicator species in relation to clean-up efforts.
The harbor porpoise is protected under the Marine Mammal Protection Act of 1972. It is a Species of Concern in Washington.
Trail work: Work has begun on improvements to Spruce Railroad Trail, now closed from the Lyre River trailhead to just east of Devil’s Punchbowl on the north shore of Lake Crescent in Olympic National Park.
Work to improve the first 1,600 feet of the trail for universal accessibility is expected to be completed by the end of October. The remainder of the trail between the Camp David Jr. Road Trailhead and Devil’s Punchbowl will continue to be open during the project.

Columnist Sharon Wootton can be reached at 360-468-3964 or
Story tags » Wildlife HabitatWildlife Watching

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