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 CCC coho back to Scott Creek, home to a coho population that spawns in the relatively small streams and creeks entering the Pacific Ocean from Punta Gorda in Northern California to Aptos, near Santa Cruz.
Coho salmon in the Scott Creek watershed have struggled to survive since the late 1800’s, 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 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 returned to Scott Creek, and the population continued to decline until no salmon returned for three years in a row, said Brian Spence, a NOAA Fisheries biologist from the Southwest Fisheries Science Center. At this point, some thought natural spawning of coho salmon in the watershed was a thing of the past.
“I think we were very close to losing not only the population of coho salmon for the Scott Creek watershed, but for the entire Santa Cruz Mountains,” said Spence. “Fortunately, improvements in fish breeding practices coupled with changes in the smolt release strategy appear to have resulted in improved success of the Kingfisher Flat Hatchery, a small hatchery located on a tributary of Scott Creek used to help restore local coho salmon populations. “
The possible solution came by way of 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 entered the ocean at different times over about eight weeks in April and May.
In contrast, the hatchery fish from Kingfisher Flats 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 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 a long period of time. This substantially increased the odds that some of the fish would arrive in the ocean when it’s highly productive.
In 2013, Spence and his colleague Joseph Kiernan tested this theory by releasing the hatchery salmon over an eight-week period, similar to the wild run timing Shapovalov and Taft had observed decades ago. If correct, they would see more coho salmon returning to Scott Creek in 2015.
So far, the results have been encouraging.
“This year we are estimating somewhere between 162 and 192 fish returning to Scott Creek,” said Spence. “That’s more than the total number of fish returns from 2006 to 2014 combined.”
Any scientist will tell you one year of data does not equal a trend. Still the researchers are hopeful.
“This is a pretty amazing response in one year simply by hedging our bets and releasing salmon over a period of time,” said Williams. “It’s the beginning of an experiment and we don’t know how it’s going to play out over time – we’re still re-diversifying this portfolio.”