Harbor Porpoises, Back After a Lifetime

 

Bill Keener works as an environmental attorney, is a former director of the Marine Mammal Center in the Headlands, and is a dear friend; we’ve been fellow poets and part of the same 8-member men’s group for 23 years.

After 65 years, harbor porpoise have returned to San Francisco Bay and are now regular visitors to Marin’s shores.  We’re fortunate—few major metropolitan areas in the world are visited by cetaceans every day.

The last time a population census was taken (in the late 1980s, when I worked as field observer aboard the survey boats), not a single porpoise was sighted east of the Golden Gate.  The species was still suffering the effects of gill net fishing, with its lethal “by-catch” of marine mammals.

Accounts say porpoise used the Bay prior to World War II, but ship traffic, pollution and submarine nets may have put an end to that. Until now. In the past couple of years, harbor porpoise have entered the Bay as far as Angel Island and Alcatraz, with reports as far north as the Tiburon Romberg Center, and even the Richmond-San Rafael Bridge.

Because porpoise are here to feed on schooling fish, they tend to stay in deepwater areas: the Golden Gate, off Sausalito, or Raccoon Straits, often waiting for the ebb tide to wash fish down out of the Bay.

The best observation spot at the moment? Cavallo Point at East Ft. Baker in GGNRA.  The best time? High tide—consult a tide table for the Gate, and then be willing to wait and watch a while.  Binoculars are a help, but sometimes the porpoises, including mothers with calves, swim very close to the rocky point.

Harbor porpoise are small dark stocky animals about 5 feet long; when they come briefly to the surface, they show a short triangular dorsal fin. They are rather shy, tend to swim quietly, and almost never “porpoise” (leap from the water).  If the water is calm and quiet, you may be able to hear them breathe (sailors called them “puffing pigs”).

Why are they back? The reasons are unclear, but we are now beginning to study them. I am currently working with two other marine mammalogists to obtain a permit from National Marine Fisheries Service that will allow us to approach the porpoises in boats and photograph them for individual identification.  We want to understand their movements and use of this new habitat.  Theories on the return range from the positive: the Bay is cleaner; restrictions on gill-netting spurred a population increase — to the negative: the drought of the past few years allows saltwater into the Bay, bringing marine fish with it; porpoise could also be fleeing the recent coastal invasion of jumbo squid which may be depleting fish stocks.

To learn more, a good reference guide, with excellent illustrations and photos, is Marine Mammals of the World by Jefferson, Webber & Pitman, Academic Press 2008.

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