Harbor porpoise sighting reported in San Joaquin River

Harbor porpoise sighting reported in San Joaquin River

LATEST Oct 24, 5:00 pm The pair of harbor porpoises spotted near the Pittsburg Marina on Sept. 29 may have traveled even farther upstream than previously thought, according to a new sighting reported to the Marine Mammal Center on Monday.

Two cetaceans matching the description of the mother and calf were observed in the San Joaquin River on Sept. 25 by an individual on a boat near Bethel Island, Bill Keener, a field researcher with the center, told SFGATE. The individual was only able to catch a fleeting glimpse of the pair as they breached.

“We’ve never had any sightings there before,” Bill Keener, a field researcher with the center, told SFGATE. “And that’s a long way upriver — 60 miles from the Golden Gate Bridge, and probably a new record.”

Previously, the farthest upstream a harbor Porpoise had been seen was in the lower Sacramento River, about 50 miles inland from the bay.

It’s not necessarily unusual behavior for the animal, which can be found all over the world. In the past, harbor porpoises have been observed swimming up the River Thames to London, Keener said. But that’s not nearly as far as the journey this pair of harbor porpoises made from the bay to the San Joaquin River.

“We want to understand why they’re going up there,” Keener said. “We still think they’re probably chasing food, but what fishes are they after? How might they be affecting the river ecosystem? How are they interacting with it? We don’t really know yet. … It just shows how important it is for the public to keep their eyes on the water, so we can make discoveries like this.”

Oct 23, 4:28 p.m. A harbor porpoise recently found its way far from home, appearing in a Bay Area waterway where the species had previously never been seen before.

On Sept. 14, the lone cetacean was spotted swimming in the Petaluma River near the yacht club with its dorsal fin just visible above the surface of the water. Customers at the nearby Grand Central café gathered outside to try to figure out what it was, as Petaluma 360 first reported, and the Marine Mammal Center subsequently received several reports of the animal.

“They wanted to make sure it wasn’t a shark, or something else,” Bill Keener, a field researcher with the center who specializes in harbor porpoises, told SFGATE on Thursday. “What was unusual about the sighting was that it was the first one ever seen that far up in the Petaluma River. That was new to us.”

On any given day, hundreds of harbor porpoises could be swimming in the San Francisco Bay, but that wasn’t always the case. The species abandoned their home near the Golden Gate Bridge at the start of World War II as large ships, submarine nets, and hundreds of underwater mines inundated and polluted the bay. Decades later, after the Clean Water Act was passed in 1972 and water quality gradually improved, harbor porpoises began to return to the bay in the 1990s.

It was around that time that Keener observed the marine mammals exploring beyond their usual range. One was spotted swimming several miles up the Napa River in 2007, reaching as far north as the Napa Town Center. Another made a similar journey to wine country in 2015 and was seen briefly emerging from the water near the Third Street Bridge.

And in July of 2021, Keener said he received a call from a fisheries biologist about yet another harbor porpoise. This time, one had been spotted in the lower Sacramento River, about 50 miles inland from the Golden Gate Bridge — the farthest upstream the species had ever been recorded in the region.

Several harbor porpoises are pictured foraging near the mouth of San Francisco Bay.

Marc Webber © The Marine Mammal Center

“I think it’s pretty interesting, because it means they’re getting more established in the bay and looking for more locations that could be good for feeding,” Keener said, noting they primarily dine upon small schooling fish like anchovy and sometimes jack smelt. “Even though they’re saltwater animals, they will go up freshwater rivers to find fish, and hopefully they make it down to the bay again. That’s what seems to have happened with the porpoise in Petaluma. It was not seen again.”

However, it wasn’t long before another pair of harbor porpoises ventured north. A suspected mother and calf were observed near the Pittsburg Marina on September 29 — the second-farthest upriver sighting documented in the Bay Area.

“In some sense, it means there are plenty of them in the bay, so there are more mouths to feed. If they’re looking for places to find food, they’ll explore,” Keener said.

He added that harbor porpoises have the shortest life span of any cetacean.

“They live life in the fast lane — they could have 10, 11 or 12 years and that’s it,” he said. “They have to breed fast and they have a high metabolic demand, so they’re always on the go, looking everywhere. The Petaluma River is a long way, but it’s not a barrier to them, by any means. The porpoise probably made that journey in a single day.”

Two harbor porpoises are pictured below the Golden Gate Bridge on December 27, 2012.

Two harbor porpoises are pictured below the Golden Gate Bridge on December 27, 2012.

Bill Keener © The Marine Mammal Center

The Marine Mammal Center encourages people to report sightings of cetaceans on its website, and is particularly interested in harbor porpoises traveling north of the Richmond-San Rafael Bridge or south of the Bay Bridge.

“If they find food, then they might return to these locations,” Keener said. “It will be interesting to see if that happens.”