KCBS News radio reported yesterday that harbor porpoises are returning to San Francisco Bay Area waters after disappearing sometime around WWII.
Historically, the porpoises were near the top of the bay’s food chain, although their remains have been found in shell mounds left by local Native Americans.
Then in WWII an anti-submarine net went up across the mouth of the bay. This, experts believe, combined with increased shipping, manufacturing and pollution, probably led to the harbor porpoise leaving the area around that time.
William “Bill” Keener of the Golden Gate Cetacean Research Center told KCBS News that this is a positive sign for the environmental health of the San Francisco Bay.
Keener said he’s been studying marine animals for many years and although he’s seen these porpoises in the ocean out at the Farallon Islands, he’s never seen them in or around the bay.
“But now they’re here every day,” said Keener. “They’re here because of fish and we can see them engaging in what we believe is feeding activity, where they’re either in areas where there’s upwelling, where the fish are being forced to the surface by the tidal currents. We’ve seen them spinning around and doing feeding activity where they’re chasing fish…. And I’m not talking about one or two animals coming in. We’re seeing thirty, forty, fifty a day.”
Keener said from this past July to November, he and his colleagues have observed both harbor porpoises and bottlenose dolphins feeding “two or three times a week” in the bay off of Fort Point.
He partially credits efforts to clean up the bay and deal with industrial or municipal sewage.
“That kind of environmental activity certainly has been a help,” he explained. “There’s probably some other reasons that are bigger than us, like the multidecadal oscillations of currents, temperatures and ocean waters have an affect on the productivity of our waters. … In addition, we stopped gillnetting along our local waters years ago. The gill nets were having a really negative affect on our porpoise and killing them. They were being caught accidentally in those nets and drowning and when that was banned in the mid-eighties their population had somewhat of a rebound.”
Keener described multidecadal oscillations as a big circulation of water in the Pacific Ocean that changes over many years. It is affected by temperature and where the currents are going and that can have really significant effects on productivity “starting from plankton, going to fish and then on up.”