Surveyors of Marin County’s endangered coho salmon had something to celebrate this year after heavy downpours allowed fish to access habitats where they haven’t been seen in nearly two decades.
“I’m very pleased with this year’s run,” said Eric Ettlinger, an aquatic ecologist with the Marin Municipal Water District who surveys the Lagunitas Creek watershed. “Even though the run seems smaller than three years ago, with all the rain, the fish were able to get high into the watershed into all the tributaries.”
“I feel their eggs will be safe for the rest of the winter and we’ll have lots of young coho next year,” he said. “And lots of people were able to see salmon spawning this year.”
There were also unprecedented sightings of the larger chinook salmon in the Redwood Creek watershed.
“I think we had something around 100 chinook in terms of the peak count on the creek,” said Michael Reichmuth, a National Park Service biologist. “It was a lot for that small of a creek, especially because they’re bigger than coho, too.”
Marin County has the largest population of Central Coast endangered coho salmon from Monterey Bay to the Sonoma-Mendocino county line. Once believed to number in the tens of thousands, coho salmon in Marin have dwindled to the hundreds. The decline is largely attributed to habitat loss caused by land-use changes and development such as dams, which blocked access to about half of the salmon’s historic habitat and caused creeks to fill in with more sediment.
Each winter, adult coho salmon enter Marin creeks after heavy rains signal them to swim upstream to spawn until about late January. After hatching two months later, the young fry rear in freshwater for about 18 months before venturing out to the ocean. After another 18 months, the fish return to Marin creeks as adults to spawn the next generation.
This year’s run of spawners left Marin creeks in 2020.
Three intense rainstorms, known as atmospheric rivers, that hit Marin from late October to December helped prime Marin’s creeks for the arrival of the salmon. In addition to clearing out the creek for easier passage and washing away algae, the rains also allowed fish to access smaller tributaries higher up in the Lagunitas Creek and Redwood Creek watersheds where they hadn’t been seen for years.
Surveyors with the Olema-based Salmon Protection and Watershed Network, or SPAWN, found salmon eggs in Larson Creek and Montezuma Creek — tributaries of San Geronimo Creek — for the first time since 2004 and 2006, respectively.
Being so far up the creeks does put the eggs and hatchlings at risk, especially during the drier summer months when creek flows diminish and sometimes dry out.
“We’re fortunate a lot of the fish did end up in the higher tributaries but it’s more prone for these fish to be stranded,” SPAWN conservation director Preston Brown said. “We have to keep a lot of attention on these upper creeks well into the spring and work with the California Department of Fish and Wildlife to get here and rescue fish. Otherwise, the benefit of getting up to these higher streams could be lost.”
The heavier storms came at the perfect time. Should similar storms occur in the coming months, the intense flows could work to wash away the eggs and the young fish. The most ideal scenario for the young fish will be several smaller storms spread out for the remainder of the winter and early spring, researchers said.
Lagunitas Creek, which has the highest number of coho in Marin, has so far seen above-average numbers of coho egg nests, known as redds. About 180 redds were counted as of last week, slightly more than the average of about 160 for this time of year, Ettlinger said. However, the count is slightly less compared to the parent generation three years ago.
This number is still well below the federal recovery target for Lagunitas Creek of 1,600 salmon redds. Surveys would need to find at least 1,600 redds for three consecutive years before the endangered status of coho could be lifted. But in more than 25 years of monitoring, the counts have never reached half that amount.
On Redwood Creek, five coho redds have been found so far but that number is expected to increase, Reichmuth said. While that count seems low, especially compared to the large number of chinook found on the creek, it is “not bad” considering the parent generation of coho, Reichmuth said.
Redwood Creek’s coho population has long struggled. In recent years, surveyors found no salmon eggs at all. In an attempt to bolster the population, hatchery-raised coho adults were released into Redwood Creek for five years. The program ended in 2019.
As in Lagunitas Creek, many coho were able to travel farther into the Redwood Creek watershed for the first time since 2004.
“They’re definitely using the watershed. I feel like I haven’t really seen that in a long time,” Reichmuth said.
Other tributaries on Redwood Creek had larger numbers of coho. Olema Creek had about 100 coho and 43 redds.
Reichmuth and his team of surveyors also found coho for the second year in a row in the smaller Pine Gulch Creek. He said it shows promise for potential repopulation of that creek.
The introduction of chinook salmon into the Redwood Creek watershed could have implications for the coho. Chinook salmon are larger and could outcompete the smaller coho for food and territory, Reichmuth said.
Researchers suspect the chinook salmon originally came from other salmon runs such as those from the Sacramento-San Joaquin River Delta. Samples of these fish have been sent to a state lab to confirm their origin.
Source: www.mercurynews.com