Biologists see increase in coho salmon in Russian River

By Brandon Beach
SPN Public Affairs Office

SAN FRANCISCO, March 15, 2011 - Nearly extinct a decade ago, coho salmon are beginning to reappear in the Russian River. Biologists with the University of California Cooperative Extension and Sea Grant Program recently recorded 34 coho at a trapping station in Mill Creek, a tributary of the Russian River. They estimate that up to 83 coho may have entered the stream, as many go undetected.

One of the adult males found was tagged with a Passive Integrated Transponder, providing valuable data about its origin. Using this PIT tag, biologists were able to trace the fish back to the 2009 smolt release by the Don Clausen Fish Hatchery. It is the first recorded return of coho in several years and marks an initial success for the U.S. Army Corps of Engineers San Francisco District-funded coho broodstock program at Lake Sonoma.

“It’s a good sign, modest as it is” said Peter LaCivita, regional fisheries biologist for the Corps’ South Pacific Division. “Will it recover the population? Only time will tell.”

Coho have come a long way since 1997, the year the Central California Coast Evolutionary Significant Unit was placed on both the State and Federal Endangered Species List, prompting the Corps and several wildlife agencies, including the National Marine Fisheries Service and California Department of Fish and Game, to establish a long-term recovery plan.

It would evolve into the Russian River Coho Captive Broodstock Program, a multi-agency effort aimed at putting coho back on the map. Since its inception, the program has completed six spawning cycles and released more than 300,000 juveniles into the tributaries of the Russian River.

In addition, the hatchery also produces 10,000 smolts every year that are released in nearby Dry Creek. The goal here is to ensure the survivability of the broodstock population with active numbers of fish returning to the hatchery to spawn.

“If your numbers are low, your breeding variety decreases,” said LaCivita. “You run the risk of having a population failure, and this population is already on life support.”

Coho typically spawn from December to January. It is during this period that hatchery biologists strip eggs from females, mix them with male sperm and monitor their growth in incubation dishes. Selecting which male to pair with which female comes down to a highly-crafted breeding matrix developed by a geneticist at the University of California, Santa Cruz.

“What we try to do is avoid inbreeding as much as possible by maximizing genetic variation,” said Ben White, a fisheries biologist at the Don Clausen Fish Hatchery.

It is the young of this broodstock population that is stocked back into the tributaries of the Russian River that historically had coho. This begins a three-year maturation cycle for coho.

“They spawn, rear in the streams, go to the ocean and come back,” said LaCivita. “That’s one of the things that make coho so vulnerable is this three-year cycle. If ocean conditions are not favorable, you could have a very poor return that year. What we’re seeing this year is we’ve had a couple of good storms early on and that’s when coho tend to migrate upstream to spawn.”

Not all of the tributaries that biologists stock with coho are monitored for returning adults, so if the findings at Mill Creek are any indicator, signs point to a very good year for coho.

Biologists measure an adult coho salmon found at a trapping station on Mill Creek, a Russian River tributary. (Photo by Mariska Obedzinski, Cal Sea Grant Program)

Biologists recorded 34 coho salmon at this trapping station on Mill Creek, a Russian River tributary. (Photo by Mariska Obedzinski, Cal Sea Grant Program)

Rory Taylor, a biologist with the Pacific States Marine Fisheries Commission, checks a tray of coho salmon alevin last year at the Don Clausen Fish Hatchery at Lake Sonoma. (Photo by Brandon Beach, U.S. Army Corps of Engineers)