(San Jose Mercury News)
Porpoises in bay waters
off Marin for first time in
60 years
By Mark Prado Marin Independent Journal
Posted: 01/22/2011 10:03:57 AM PST
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
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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 h
as 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!'"
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