Record-breaking rainfall flooded much of the Bay Area in late October and again around Christmas, resulting in flooding, power outages, troublesome traffic – and a great season for a struggling fish. these last years.
For chinook salmon heading for East Bay, which comes up in the fall, which relies on continuous pulses of fresh water to allow it passage to the spawning grounds upstream, the October rain could not have been better. moment.
“This year is a bit of an anomaly, looking at the past 25 years,” said Jeff Miller, founder and executive director of the Alameda Creek Alliance. In recent years, rain in the Bay Area has fallen frequently outside of the main spawning season for fall return chinook salmon. As a result, returning salmon were unable to enjoy the highest freshwater flows during those years and had to contend with drier conditions during their migrations.
But this year was different. The rain fell relatively early, preparing the streams for Chinook salmon to migrate inland. Alameda Creek, which typically sees a small handful of chinook salmon during a typical migration season, has instead seen about three to four dozen chinook salmon this year, Miller said.
On this journey, the fish leave the salty water of the Pacific Ocean behind, swim under the Golden Gate, and move up streams to seek suitable freshwater habitats where they will spawn, lay eggs – a single salmon. can lay up to 20,000 eggs – and eventually die.
During these seasonal migrations, most chinook salmon are instinctively guided to specific freshwater sites where they themselves have hatched, often three or four years before their final return. Salmon spend most of the time in the Pacific Ocean, dodging predators such as seals, sea lions, killer whales, and fishermen, and feeding on crustaceans and small fish such as anchovies.
“Scientists believe that this incredible feat of salmon making their way to their native stream is in large part due to a keen sense of smell,” wrote George Neillands, senior environmental science supervisor for the California Department. of Fish and Wildlife Bay-Delta, in an email. “Salmon’s imprint on the unique chemical makeup of their native stream water, and adult salmon recognize this information as a clue to direction during their migration. “
While the vast majority of chinook salmon that enter San Francisco Bay swim to the Sacramento and San Joaquin rivers, making their way to the Central Valley hatcheries where many have hatched, chinook salmon also occasionally stray to sea. other freshwater coves in the bay area, Miller said. These routes include the Alameda Creek, Guadalupe River, and Los Gatos Creek in the South Bay, and many more – just about “anything that has a decent flow,” Neillands added.
This year’s South Bay salmon counts have been more consistent than in previous years. Steve Holmes, founder and executive director of the South Bay Clean Creeks Coalition, said his organization is on track to see 150-200 salmon this year along the Guadalupe River and Los Gatos Creek, and he notes that he “can only speculate” as to why South Bay’s numbers did not increase this winter like East Bay did.
Even Lake Merritt, a tidal lagoon in Oakland that connects to the bay via a flood control valve operated by the Alameda County Flood Control District, saw about four Chinook Salmon after the October rains. . “Who would have thought there would be chinook salmon in Lake Merritt, and now they’re here.” It’s just amazing, ”said Katie Noonan, Friends of the Nature Center of Rotary co-chair. Noonan said it was not the first time chinooks have been spotted at Lake Merritt, but large fish are rare in the lake, and when spotted it creates a lot of excitement.
While the chinook salmon’s fall migration is largely over, coastal small coho salmon are completing their winter migration in streams such as Lagunitas Creek in Marin. Neillands said an email from the Marin Municipal Water District reported that in two days in December, 195 coho salmon and 67 spawning grounds (spawners) were counted in Lagunitas Creek, San Geronimo Creek and Devil’s Ravine – a good december for the coho salmon in these streams.
While coho salmon prefer coastal streams when migrating to spawn, fall chinook migrate inland, and their passage to suitable spawning habitat often requires several storms. Even with the October rain, numerous obstacles continued to hamper the progress of Chinook Salmon in search of upstream sites in the Bay Area.
Chinook salmon traveling in the South Bay face large amounts of litter, especially in the highly developed parts of the San José area, Holmes said. Noonan said the litter around Lake Merritt also puts the welfare of the lake’s fish and wildlife in question.
Additionally, Holmes said drought-stressed lands tend to easily absorb the first rainwater of the year, leaving less water available to contribute to the constant freshwater flows that fall salmon depend on. to move upstream. Sometimes there is only a “river feather” through which only the smallest fish can swim successfully, Holmes said.
For East-Bay-bound chinooks moving up Alameda Creek, a 12-foot impassable BART cement spillway forms an “absolute barrier”, preventing all migratory fish other than Sucker Lamprey from accessing better quality water. upstream, Miller said.
The chinook salmon that made up Alameda Creek this year have been stuck behind the BART Weir since the October rains. “They jump and jump on this barrier and they cannot cross it. They come back down, get exhausted – it’s just heartbreaking to see it, ”Miller said.
A $ 40 million fish ladder is currently under work at the BART spillway site, and Miller said he expects the ladder to be fully functional for the fall chinook migration of 2022. This fish ladder is a vital piece of the puzzle when it comes to restoring the ability of Chinook Salmon to migrate through Alameda Creek to the Upper Watershed to the Sunol Wilderness, a lost migration route. for about 50 years.
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The CDFW oversees the release of several million hatchery-reared chinook smolts each year, Neillands wrote. The Feather River hatchery alone produces nearly 8 million fall return chinook salmon per year, he added.
Alameda Creek fall return chinook, many of which are from hatchery original lines, are not considered native and do not qualify for CDFW permits that would allow their release upstream. blocking of the BART weir. In contrast, the Alameda Creek rainbow trout, considered native and threatened, are granted permits by the CDFW, which allows their upstream release, in which the Alameda Creek Alliance has been involved for some time. years. In fact, the new fish ladder is primarily intended to help the rainbow trout – the salmon will only benefit.
“These are difficult times for an organism dependent on freshwater,” Miller said, even when the weather is favorable. At the same time, he added, watching Chinook Salmon in the Bay Area gives everyone a glimpse into the connectivity and health of the Bay Area’s waterways. “They are, he says, very good ambassadors for the protection of our coves.