Bottlenose dolphins seen off Sonoma Coast part of closely watched northward push
Stunning images of bottlenose dolphins leaping and surfing in heavy waves triggered by an underwater volcano earlier this month proved a surprise to some casual observers off the Sonoma Coast.
“What? We have dolphins now?” was one question posed as photos of the pod cavorting at Salmon Creek Beach near Bodega Bay made the rounds.
Yes, is the answer, but only over the past decade, as part of a closely watched shift in the range of near-shore dolphins long common to the warmer waters off Southern California and the border region of Mexico.
A handful of residents at The Sea Ranch on the north Sonoma Coast got a show themselves in mid-January, when a pod of dolphins with a newborn calf spent most of the day frolicking off Walk On Beach.
“It was thrilling,” said Karen Wilkinson, who witnessed the event ― her fifth experience seeing dolphins off the coast in that area.
California Coastal Bottlenose Dolphins, a genetically distinct stock estimated to number only about 650 individual animals, were not even documented north of Point Conception, near Santa Barbara, until 1983.
But with each pulse northward, typically during warm water events, the animals appear to adapt to their new surroundings and linger on, expanding their range by nearly 500 linear miles in less than 40 years.
“It’s a complicated and interesting story that’s unfolding right now in front of us,” said Bill Keener, a member of the Cetacean Field Research Team at The Marine Mammal Center in Sausalito and leader of long-term study of the population’s range expansion. “But also, from a personal point of view, it’s really neat to be able to go out and see really interesting, big animals from the beach, from the headlands. To be able to see these guys go by. I just think it’s fascinating.”
Prodded northward in the past when marine temperatures rose, the projected increase of such events suggest additional progression in the future.
“If seas keep warming, they could make their march north,” Keener said.
Coastal bottlenose inhabit a very narrow band of water along the coast, he said. Their traditional range is from about Eseñada, in Baja California, to Point Conception.
From a few that strayed north to Monterey Bay during an El Niño event in 1983, they continued creeping north over the years, becoming increasingly common off the Central Coast.
The first was one was recorded in San Francisco Bay in 2001, where they became regulars around 2010, inspiring Keener, one-time director of The Marine Mammal Center, and a group of collaborators to launch a study that they hope to publish later this year.
A marine heat wave in the mid-2010s, sometimes known as “the warm blob,” seems to have established the species on the Sonoma Coast, even though the first recorded sighting north of San Francisco Bay was a mere a decade ago, in July 2012.
That summer, a dolphin dubbed “Smootch,” distinguished by its serrated dorsal fin and last observed in Southern California before that, was photographed off Doran Beach. She was spotted twice more closer to San Francisco Bay over the ensuing year.
But it was in the following three years, during a prolonged marine heat wave that disrupted the entire marine environment ― upending normal cycles, spurring marine mammal strandings and severe, sudden population shifts ― that a sizable number hit the Sonoma Coast, Keener said.
Some went beyond, reaching Mendocino County briefly, while a few wandered clear to Puget Sound, in Washington State, including one nicknamed “Miss” and last seen that year.
The animals live up to 50 years, and their dorsal fins become so uniquely weathered, scarred and ragged that scientists are able to track them over time through distinguishing photographs.
About 120 bottlenose dolphins have been documented in the greater Bay Area, and about 453 have been cataloged in total, Keener said.
That’s how scientists know, for example, how well traveled Smootch was between 1984 and her last sighting in 2013.