Heavy rains could harm Marin salmon, steelhead recovery, surveyors say

The deluge of rain this winter may act as a double-edged sword for the recovery of protected fish runs in the Lagunitas Creek watershed, according to Marin County fish surveyors.

The strong rains ramped up stream flows, allowing spawning fish such as steelhead and endangered coho salmon to reach their spawning grounds. However, the historic loss of floodplains by development and dams in the watershed has resulted in rainfall concentrating into much stronger flows, which can scour creek beds where steelhead and salmon bury their egg nests, also called redds.

This year is being called the watershed’s best spawning season for endangered coho salmon in 12 years, and surveyors are concerned that recent powerful storms and resulting high flows could harm the newly hatched salmon fry and the thousands of precious eggs incubating in local creek beds.

Michael Reichmuth, fisheries biologist for the Point Reyes National Seashore, said the flows he and other researchers saw on the Olema Creek tributary were at a level they would normally see once every decade or so.

“Some may wonder what this means to the salmon,” Reichmuth wrote in an email. “For adult steelhead it means plenty of habitat to work with for spawning if they are entering the creeks now. For the eggs and fry that are currently emerging from nesting sites it could mean the end of their life.”

The rains also engorged Lagunitas Creek to peak flows of about 4,100 cubic feet per second, which is the level seen every eight years or so, according to Marin Municipal Water District aquatic ecologist Eric Ettlinger.

“Past floods like this have mobilized streambed sediment, either uncovering or entombing incubating salmonid eggs, and resulted in survival rates of only about 2 percent,” Ettlinger said.

But Ettlinger said there are encouraging signs that this will remain a good year for coho recovery. About 600,000 coho eggs are estimated to have been deposited during this year’s winter coho run, and Ettlinger said survival rates don’t have to be high to produce normal numbers of fry.

“The biggest risk now is that a late-season storm will wash out coho fry after they’ve emerged from the gravel,” Ettlinger wrote in an email.

Downed trees, wood and other debris in the creek can provide shelter for the young rearing fish during floods and strong flows.

“In the summer time when the flows have receded we will be able to take inventory on the habitat and remaining fry to give us insight on how detrimental these floods were on the population,” Reichmuth said.

While the coho spawning season ended last month, steelhead spawning is ongoing. Surveyors haven’t had many chances to count fish because of the storms and high flows. By the end of February surveyors had found about 99 steelhead redds, which Ettlinger says is average.

National park fish surveyors have only been able to conduct a few surveys on the Redwood Creek watershed and on the Chelda Creek tributary, but have not been able to go out for several weeks due to the high flows. Total counts so far show 45 steelhead adults, one carcass and 13 redds on Redwood Creek. One steelhead and one steelhead redd were also found on Chelda Creek.

Both Reichmuth and Ettlinger said they hope to do more surveying once the flows recede.

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