Porpoises in bay waters off Marin for first time in 60 years

MercuryNews.com: Porpoises in bay waters off Marin for first time in 60 years
After an absence of more than 60 years, harbor porpoises are returning to the bay waters off Marin in what could be a sign of a healthier ecosystem.

A pair of local researchers -- William Keener of Corte Madera and Jonathan Stern of San Rafael -- have been studying the return of the marine mammals for more than a year.

Historically porpoises were seen off Tiburon and Belvedere; American Indians who lived on the bay would use them as a food source.

But in the 1940s the local porpoises began to disappear. The most common theory is that as World War II raged, there was a hub of activity near the Golden Gate Bridge: There was a net underneath the span to keep enemy submarines out, military ships came and went and the outer Golden Gate was speckled with 600 floating mines.

"You can imagine the porpoises had to maneuver around all this to get into the bay, and they couldn't," said Stern, a member of Golden Gate Cetacean Research, a private research group studying the species. "A bulk of their prey was excluded from the bay as well. Eventually they were squeezed out."

Populations were further hurt by gillnetting in the decades after the war, but as that practice stopped in the 1980s the population grew stronger came back.

Now they have started to reappear in the bay.

"They may be looking for more places to feed now," Keener said. "At the same time the bay seems to be in a period of productivity. There is a lot of crab in the bay right now and a lot of fish, and the porpoises are after food and following fish into the bay."

Porpoises are not rare in Northern California, but their reappearance in the bay has been a surprise.

"Their range is along the coast, so it's not as though they have moved 10,000 miles, but they have moved that important mile and it brings them into a different system," Stern said. "They are following prey, but once they are in the bay they can find other things to feed on."

The porpoises like to eat sardines, anchovies and any type of small schooling fish. More than 125 porpoises are believed to be in the bay; there are an estimated 9,000 along the coast from San Francisco to the Russian River.

The dark gray, 6-foot-long porpoise is hard to see in the wild, but land masses and bridges in the Bay Area give a unique chance to view the species, which travels in small groups of two and three, but sometimes mass to feed. Yellow Bluff near Horseshoe Cove at Fort Baker has been a hot spot for porpoises, but it is treacherous as a viewing area. The best spot to see porpoises is from Cavallo Point near Fort Baker in Southern Marin.

"If you stand right at the end of the point and are there at the beginning of ebb tides you can see them go by," Keener said.

The porpoise behavior in the bay is with purpose, the researchers said.

"They always seem to have some appointment to go to, they are always on the move," Stern said. "They are really squirrely."

But the bay has proved to be a good spot to study the animals. The seas are relatively flat and the bay has defined parameters, limiting where they can go.

"But we are not chasing them," said Stern, noting researchers have a federal permit for their work. "But they seem not to be bothered by vessel traffic, so our little research boat does not bother them."

The researchers want to track the porpoises -- which can live up to 12 years -- over a decade to determine calving rates. Monitoring their behavior and populations could render valuable data.

The federal Gulf of the Farallones Marine Sanctuary, a partner in the project, is interested in the research. In particular it is curious whether porpoises from waters outside the Golden Gate are expanding their range voluntarily, if they are increasing in numbers or being pressured into finding alternate feeding grounds.

"They could be very good environmental indicators of the ongoing health of the bay," said Mary Jane Schramm, sanctuary spokeswoman. "If they suddenly disappear that will tell us something about the bay and the Gulf of the Farallones as well."

The return of the porpoises is a bit of good news in these days of threats of eco-calamities.

"It's something the environmental movement really needs," Stern said. "Everything is so depressing, so it's nice to know everything is not bad. This is like, 'All right, go porpoises!'"