Researchers Borrow Investment Strategy to Save Salmon Stock

May 2016

Financial management may seem an unlikely source of strategies to save a wild population of salmon from extinction, but a group of NOAA Fisheries researchers is using a key financial lesson to restore Central California Coast (CCC) coho salmon in a small stream just 50 miles south of San Francisco.

“It’s called the ‘portfolio effect,’” said Tommy Williams, a Research Fisheries Biologist at NOAA’s Southwest Fisheries Science Center. “It’s the concept of comparing biodiversity to stock holdings, where diversification reduces risk to the investment, or in this case, risk to the population of coho salmon.”

The idea is helping bring coho salmon back to Scott Creek and other watersheds in the Santa Cruz Mountains. These populations constitute the southern end of the CCC coho salmon’s historical range, which includes streams and rivers entering the Pacific Ocean from Punta Gorda in Northern California to Aptos, near Santa Cruz.

Coho smolts

Coho salmon smolts just released from a hatchery

Coho salmon in Scott Creek and other local watersheds have struggled to survive since the late 1800s, when heavy logging of redwood forests to build nearby San Francisco degraded much of their natural spawning habitat. Continued urbanization and water quality degradation pushed the species closer to extinction. In 1996, CCC coho salmon received federal protection under the Endangered Species Act as a threatened species. It was reclassified as a species in danger of extinction in 2005.

In 2006 just 42 coho salmon returned to Scott Creek, and over the next six years, only a few adult females returned to the stream, said Brian Spence, a NOAA Fisheries Biologist from the Southwest Fisheries Science Center. During this period, it is believed that little if any natural reproduction was occurring in watersheds south of the San Francisco Bay. Virtually all remaining fish in the region were the result of a small hatchery program that is jointly operated and funded by NOAA Fisheries, the California Department of Fish and Wildlife, and the Monterey Bay Salmon and Trout Project, a local non-profit organization that runs the Kingfisher Flat Hatchery on Scott Creek.

“I think we were very close to losing not only the population of coho salmon for the Scott Creek watershed, but those throughout the entire Santa Cruz Mountains,” said Spence. “Fortunately, recent improvements in fish breeding practices coupled with changes in the smolt release strategy appear to have resulted in improved success of the hatchery program.”

The possible solution has its roots in a 1954 California Department of Fish and Game publication by biologists Leo Shapovalov and Alan C. Taft, who showed that wild juvenile coho salmon from nearby Waddell Creek routinely entered the ocean at different times within an eight-week period spanning from April to early June.

In contrast, the hatchery fish from Kingfisher Flat zoomed out of Scott Creek and into the ocean almost as soon as they were released in mid-to-late March.

“This meant the entire salmon population released from the hatchery was at the mercy of whatever ocean conditions and food productivity were available at that specific time smolts entered the ocean,” said Williams. “In a financial sense we were essentially risking all our stock in one company and hoping for the best – it could be boom or bust.”

Recently there had been more busts than booms. For instance, in 2006 the hatchery released more than 25,000 smolts into Scott Creek, but only 18 adult fish, all males, came back in 2008.

Scientists theorized the wild coho salmon Shapovalov and Taft observed had evolved to migrate to the ocean over an extended period in response to variable and unpredictable ocean conditions during the spring. That unpredictability is tied to the onset of spring upwelling off the Central California Coast, which drives production of the foods that young salmon eat after entering the ocean. Spreading the migration out through time may increase the odds that some of the fish will arrive in the ocean when it is most productive.

In 2013, Spence and his colleague Joseph Kiernan began testing this theory. During the last four outmigration seasons, they have released the hatchery salmon over an eight-week period, similar to the wild run timing Shapovalov and Taft had observed decades earlier. Their prediction is that, over the long term, such a strategy will improve the overall marine survival rate of these hatchery fish.

So far, the results have been encouraging, though somewhat mixed.

“For the 2014-2015 spawning year, we estimate that approximately 165 adult coho salmon returned to Scott Creek,” said Spence. “That’s more than the total number of fish returns from 2006 to 2014 combined.”

“Further, we have evidence that some returning adults strayed to other watersheds in the Santa Cruz Mountains and successfully reproduced,” added Kiernan, noting that either adult salmon or their progeny were observed in seven different watersheds as a result of the 2014-2015 returns.

Importantly, the results indicate that, for the 2013 releases, those fish released late in the spring survived at more than double the rate of those released early in the season, lending support to the notion that spreading the releases through time improved overall marine survival.

Results from the second year of releases (2014) were more equivocal. In 2015-2016, NOAA survey crews documented approximately 30 spawning nest or “redds” in the watershed that they attributed to coho salmon, a number that is down from the previous year. However, high stream flows during the spawning season greatly hindered detection and recovery of tagged fish in Scott Creek. Thus, data on which release groups were best represented in the returning fish is limited. Though the lower returns were somewhat discouraging, Spence and Kiernan suspect that they were likely attributable unusually warm ocean conditions that prevailed off the coast from late summer/fall 2014 through 2015 and that produced extremely low returns of coho salmon in populations spanning from California to Washington.

Despite the relatively low returns this past year, the researchers remain optimistic.

“This is a pretty amazing response in just a few years simply by hedging our bets and releasing salmon over a period of time,” said Williams. “Not every year will be a boom year. But we are hoping that by re-expressing the diversity of run timing that historically occurred we will increase the likelihood that every year some fish will enter the ocean at a time when ocean conditions are favorable. It’s still the early stages of an experiment and we don’t know how it’s going to play out over time – we’re still re-diversifying this portfolio.”

Learn more:

Species in the Spotlight: Central California Coast Coho Salmon

Contact: SWFSC Fisheries Ecology Division, Landscape Ecology Team

Last modified: 8/10/2016