Spawner population crash – Biologists concerned about record-low coho counts West Marin

By January 24, 2008Uncategorized

Fish biologists in West Marin are expressing concern over what is shaping up to be one of the worst coho salmon spawning years on record.

Numbers of new nests are way down in Olema Creek and the San Geronimo Valley. But causing the most alarm is Redwood Creek near Muir Beach, where no coho have been observed for the first time since formal surveys began in 1994.

“It’s pretty depressing, actually,” said Mike Reichmuth, a fisheries biologist with the National Park Service. “We’ve never seen this before [at Redwood Creek]. It had always been considered the southernmost stable population.”

Biologists acknowledge that fish counts are inexact, and that some salmon may still make their way upstream before the spawning season ends. But comparing the results of this year’s surveys with those from three years ago – when the life cycle of the current year-class began – the numbers tell a clear story:
By this time three years ago, Redwood Creek already had more than 100 redds – or nests where female coho lay their eggs – compared to zero so far this year.

In the Olema Creek mainstem, observers three years ago had counted more than 90 redds, compared to only 16 as of this week. And in tributaries to the San Geronimo Creek, surveys spotted more than 120 redds three years ago – compared to only nine so far this year.

Paola Bouley, watershed biologist with the Salmon Protection and Watershed Network (SPAWN), said that this year’s surveys have produced the lowest number of redds ever counted in the area. The drop is particularly troubling because three years ago saw a record spawning run in Lagunitas Creek, with the most redds in 14 years of counting.

“Basically, this went from being our best year-class to our worst year-class,” Bouley said. “When you start to look at the numbers in that context, the data is clear. Something is definitely going on out here.”

Poor ocean conditions blamed

Largely because of human-induced habitat impacts, the California coho population is believed to have undergone a 90 percent decline in the half-century afterWWII. The geographical coho population from Santa Cruz to Humboldt County is now listed as a federally endangered species, and over the last decade numerous restoration efforts have taken root.
No one can be certain about the exact cause of this year’s steep decline in numbers, but biologists believe that poor ocean conditions two years ago may have taken its toll on the population.

Coho salmon have a very predictable life cycle, spending their first year in and around stream tributaries before making their way out to sea. Then, in their third winter, adult salmon return from ocean feeding grounds to spawn in the freshwater streams of their birth.

Winter floods in early 2006 did have an impact on survival rates for the year-old juveniles. But biologists were monitoring how many fish exited into the ocean, and counted more than 6,000 coho that spring.

They believe that the small number of salmon returning this year has more to do with poor ocean conditions in 2006, which limited the amount of available food and caused a big bird die-off – often a reliable predictor of fish health as well.
In fitting with this pattern, Reichmuth said he has heard that salmon numbers are down this year all along the California coast.
“It sounds like up and down the coast it’s the same story,” he said. “It appears to be a general trend.”
West Marin fish advocates were hoping that the heavy rainstorm during first week of January would attract a big pulse of coho upstream, but subsequent surveys saw only a few new salmon.

Ironically, early steelhead trout numbers appear to be strong throughout West Marin this year. But, because their life cycle is not as strict as that of the coho, one year of bad conditions does not affect their population as dramatically.
Reichmuth plans to conduct another coho survey in Olema Creek this week, and said he will keep doing so until he stops finding any new activity. However, both he and Bouley said they do not expect to see much more this season. Coho spawning usually peaks around the turn of the new year, and ends about mid-January. They said it was virtually unheard of to see any new fish in February.

What next for Redwood Creek?

Last week, Reichman received reports of a river otter eating a coho in Redwood Creek. He went out to conduct another survey on Friday and found four steelhead carcasses, but still no signs of salmon.

He said the park will search for juveniles in Redwood Creek through the summer, just in case they missed any nests this winter. If no juveniles appear, they will consider ways to accommodate the lost year-class — including, possibly, introducing coho juveniles from elsewhere.

For her part, Bouley speculated whether the Redwood Creek situation was exacerbated by this fall’s Cosco Busan oil spill, which sullied the waters of Muir Beach. She said SPAWN is considering writing a letter to state and federal fishery managers to ask that they investigate the impacts of the spill on the coho population.

In the meantime, Reichmuth said it is critical that West Marin residents be aware of the tenuous situation for this year’s coho.
“We definitely need to watch what we’re doing around the creeks,” he said. “We need to do whatever we can to protect these fish and give them the best opportunity to bounce back.”
Reichmuth noted that many populations are naturally cyclic. But he said this year’s crash was particularly troubling because the overall coho population is already so low.

“If you have a population that’s not viable to begin with, then it might not be able to recover from a bad year because there’s nothing to ride back up,” he said.

Bouley said the numbers underscore the coho’s dire vulnerability.
“It’s pretty distressing,” she said. “Here we’ve been celebrating the recovery of coho in the past decade, but with Redwood Creek now we may have lost an entire year-class, which is a pretty bad situation when you’re trying to protect an endangered species.”
“When you have a population that only grows to three years old,” Bouley added, “two or three bad years in a row could wipe the species out.”