Harbor porpoise a rare sight in Puget Sound

SHARON WOOTTON

Originally published Tuesday, March 12, 2002

It was the color that caught my eye.

The gray was out of place, a bit too far out to be a rock on the shoreline, the wrong color to be part of the log against which it bumped so gently.

Peering through binoculars triggered a suspicion. Wrestling it to land confirmed it. The out-of-place color was a dead harbor porpoise.

If harbor porpoises and orcas were in the same movie, the orca would be the star and the harbor porpoise an extra. We know more than we can remember about orcas, but comparatively little about harbor porpoises.

Wildlife biologist Brad Hanson of the National Marine Mammal Laboratory in Seattle, part of the National Marine Fisheries Service, can be very creative when it comes to studying marine mammals.

In 1996, he used a wind tunnel and a porpoise model to study the aerodynamic drag on radio telemetry tags.

Harbor porpoises were the most commonly observed marine mammal in Puget Sound in the 1940s. Since the '60s, they've been essentially extinct from central and south Puget Sound.

There are many possible causes, Hanson said, citing gillnet fisheries of the 1940s and 1950s, boat noise, possible change in food base, and contaminants.

Increased human population in the San Juan Islands, Bellingham and Victoria, British Columbia, may put the northern population at risk.

Population surveys haven't been conducted in Puget Sound by the agency since 1994, which led to the conclusion that the resident population is near zero, Hanson said.

It's estimated that there are 1,600 in the San Juans, 1,900 in the U.S. straits and 1,200 in the Canadian straits, Hanson said.

Family ties of the smallest cetacean in the Pacific Northwest are basically a mystery, except that the social structure is very different from killer whales.

"My impression in the tracking work (is) that there may be a larger group structure, but it's all spread out over a larger area. They don't group up in tight formation like killer whales," Hanson said.

Through autopsies, biologists know that harbor porpoises eat small schooling fish such as herring, pollack and hake. And the tiny black-bellied eelpout. Solitary as adults, they must be schooling as juveniles.

"The bottom line is that virtually every stomach that we get (of the 50 percent that have food in them) has black-bellied eelpout. One Dall's porpoise had 1,600 in its stomach."

Harbor porpoises are relatively short-lived, about 10 years. Adults are about 5 feet long, but large females may reach 6 feet. On long dives, they may go as deep as 600 feet, but lack of studies makes that more guesswork than fact.

Biologists have discovered that Dall's and harbor porpoises have hybridized.

"Hybrids look like a harbor porpoise except the coloration is like a cup of coffee with some cream in it," Hanson said. "They act like and hang out like Dall's porpoises. It's very bizarre."

So what happened to my porpoise? I called the San Juan County Marine Mammal Stranding Network at the Whale Museum, and Albert Shepard and Soundwatch coordinator Kari Koski Wirka motored over to retrieve the body.

It was sent to the National Marine Mammal Laboratory, where Hanson will perform an autopsy in the next few weeks.

Sharon Wootton lives on Shaw Island. She can be reached at songandword@ rockisland.com or 360-468-3964.

The Olympian Copyright 2002

back to Critters index