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To the delight of animal lovers and cetacean researchers, harbor porpoises and bottlenose dolphins have found new habitats in San Francisco Bay and are now regularly seen foraging for fish and body-surfing in boat wakes under the Golden Gate Bridge.
Harbor porpoises, among the smallest of the world’s six porpoise species, first re-appeared in 2008, after a more than 60-year absence. The appearance of the bottlenose dolphins in 2010, in contrast, is believed to be associated with a range expansion of the species. Prior to the 1982-83 El Niño, the dolphins were rarely found north of Point Conception, according to scientists.
“I am not talking about seeing one or two animals,” William Keener with Golden Gate Cetacean Research said at the recent State of the Estuary Conference in Oakland. “I am talking about people watching a hundred (porpoises) go by in two hours.”
In the last few years, he and colleagues have amassed the world’s most comprehensive photographic catalog for the harbor porpoise. About 600 individuals have been identified by their scars and pigmentation patterns. Similar photographic cataloging has not been possible in other parts of the world.
“We’ve had the luck of having the world’s greatest observing platform that nobody knew about,” Keener said. “From the pedestrian deck of the Golden Gate Bridge, we can watch them go about their business and they don’t know we are there.”
The photographic database is making it possible to address critical questions about the porpoise’s life history, such as whether females give birth yearly, as do their counterparts on the East Coast, or every other year, as has been suggested by others.
About 41 bottlenose dolphins have also been photographically “fingerprinted.” At an upcoming marine mammals conference in New Zealand next month, Isidore Szczepaniak with Golden Gate Cetacean Research and colleagues will report a new longshore movement record of about 1,000 kilometers for one dolphin. “Smootch” was photo-identified in Ensenada, Mexico in 2000 and in Bodega Bay in 2012.
“We are seeing a lot of dolphins go back and forth between San Francisco and Monterey bays,” Szczepaniak said. “We’d like to know how often and their speeds.”
Besides studying the cetaceans’ many fascinating behaviors, scientists also hope to figure out what exactly attracted the top predators to the region.
The leading theory is food. Low rainfall in 2007-09 might have expanded salt-water habitats in the bay for schooling fish such as herring. Dolphins have also been observed snacking on Chinook salmon in the bay.
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Calling all citizen scientists! Golden Gate Cetacean Research is collecting interesting or unusual sighting information on porpoises, dolphins and minke whales in the San Francisco Bay and along the coast. Click to report a sighting. For more information, contact William Keener, Golden Gate Cetacean Research, bill.keener@comcast.net, (415) 297-6139.
Written by Christina S. Johnson