Hatchery fish outnumber wild chinook salmon in troubled fall run

Hatchery controversy takes on new significance as salmon populations crash

SANTA CRUZ, CA--A recent study indicates that wild salmon may account for just 10 percent of California's fall-run chinook salmon population, while the vast majority of the fish come from hatcheries. The findings are especially troubling in light of the disastrous decline in the population this year, which will probably force the closure of the 2008 season for commercial and recreational salmon fishing.

The role of hatcheries in the management of salmon populations has been a contentious issue for many years. The new findings appear to support the idea that including artificially propagated fish in population estimates can mask declines in natural populations caused by a lack of suitable habitat.

"Our finding that 90 percent of the fish are from hatcheries surprised a lot of people," said Rachel Barnett-Johnson, a fisheries biologist with the Institute of Marine Sciences at the University of California, Santa Cruz.

Barnett-Johnson and her coworkers published their results in the December 2007 issue of the Canadian Journal of Fisheries and Aquatic Sciences. The main focus of the paper is the development of a new technique for distinguishing between wild and hatchery-raised salmon. The researchers validated the technique and used it to estimate the percentage of wild fish among the fall-run chinook salmon caught by commercial fishing boats along the central California coast in 2002.

"It's a one-time estimate for that year, and these things do change over time. But it's the most recent and perhaps best estimate we have," said Churchill Grimes, director of the National Marine Fisheries Service Santa Cruz Laboratory and a coauthor of the paper.

In 2002, the fall run of chinook salmon in the Sacramento River was estimated at 775,000 adults returning to spawn, according to the Pacific Fisheries Management Council. Fewer than 60,000 are expected this year, even with no ocean fishing allowed. If the percentage of wild fish is the same this year as in 2002, it would mean fewer than 6,000 wild salmon in what has been the largest salmon run on the West Coast.

The researchers were able to distinguish between wild and hatchery-raised fish by analyzing the banding patterns in fish ear bones, called otoliths. Like tree rings, characteristic light and dark bands in the otoliths reflect daily growth increments, and the width of the bands indicates growth rates. The differences observed between otoliths from wild and hatchery-raised fish are the result of differences in the availability of food at a critical transition in the salmon life cycle, when the young fish (called fry) have used up the food supply in their yolk sacs and must start feeding themselves, Barnett-Johnson said.