With the nation busy fighting a war, the kinetic pace of [San Francisco Bay] had a profound impact on the wildlife that called the bay home, marine biologists say. So-called apex predators such as the harbor porpoise were seen less and less.
“We don’t know why they disappeared. … It’s very possible that they just abandoned the place because it became too hard to feed, reproduce and raise their young,” said William Keener, a co-investigator and spokesman with the nonprofit Golden Gate Cetacean Research group.
Then all of a sudden, the porpoises were back.
Local marine biologists began noticing the presence of the shy creatures inside the bay a few years ago, Keener said. By the fall of 2009, members of his group were regularly observing them underneath the Golden Gate Bridge and around the Angel Island area.
Scientists conjecture that bay water quality may have had something to do with the disappearance. If anything, it got profoundly worse in the decades after the war, but it’s started to improve in recent years.
Others have theorized that global warming and rising sea temperatures are the reason for the shift.
And yet others say that as less freshwater comes downstream from the Sacramento-San Joaquin River Delta and its tributaries, the bay holds a greater percentage of saltwater. Such a change could mean more cetacean prey species inside bay waters. According to Keener, at least one other larger marine mammal has been spotted inside bay waters: the California bottlenose dolphin.
Now, more than 65 years after the war, the exact reason that harbor porpoises have returned remains a mystery.