January 10, 2012
Large numbers of porpoise corpses have been washing up along the San Francisco Bay, and biologists claim that bottlenose dolphins are to blame.
When the carcasses of five battered porpoises turned up within the month of August, biologists took note of the spike in brutality between the two mammals. This bizarre event is accompanied by another unprecedented occurrence: the reemergence of harbor porpoises which, until recently, hadn’t been sighted within the San Francisco Bay since the 1930s.
One theory links the porpoise’s disappearance to the ship-building frenzy of World War II. Another claims that water pollution may have been the culprit, and that the species' return is a result of the Clean Water Act of 1972. Whatever the reason, porpoises have returned to San Francisco Bay, only to be fatally bullied and often brutally sexually assaulted by the resident bottlenose dolphin population. The newcomers are allegedly being accosted by young, male dolphins who, for reasons unknown, brutalize the smaller animals physically and sexually.
And the disturbing behavior isn't just playing out in the Bay Area. The dolphin attacks have also been documented in Monterey Bay, as seen in the following video.
"You've got two marine predators who are sharing the bay again. That's really interesting, but when they come into contact, there is going to be some conflict and the loser is going to be the porpoise," said Bill Keener, a Golden Gate Cetacean research scientist, in an interview with SFGate.
Porpicide, the intentional killing of porpoises by dolphins, has been documented worldwide since 1991, but its frequency within the San Francisco Bay has some biologists alarmed, while others have accepted the killings as a natural phenomenon that is unavoidable when two predators share an environment.