Hatchery fish outnumber wild chinook salmon in troubled fall run

Fisheries experts blame unfavorable ocean conditions for the dismally low returns of chinook and coho salmon to rivers and streams all along the West Coast this year. In 2005, when this year's returning salmon were juveniles just entering the ocean, food production in the California Current was much lower than usual due to a delay in the wind-driven upwelling of nutrient-rich water that sustains the food web along the coast. A similar disruption of the normal upwelling occurred the following year (see earlier press release at http://press.ucsc.edu/text.asp?pid=971).

"We expect the returns to be as bad or worse next year as they were this year," Grimes said. "The years when those fish outmigrated into the ocean were the worst conditions that we've seen in over 25 years of observing spring conditions."

Compounding the situation is the degradation of the freshwater habitat for salmon in the Sacramento River and the rest of the Central Valley drainage system, he said. "There is no question that the river basin's capacity to produce salmon--the quality of the habitat--has been degraded something awful, and it just doesn't produce like it used to," Grimes said. "We have these remnant populations--that's all it is really. We're trying to manage what's left."

Barnett-Johnson said the otolith technique offers a new tool for monitoring the effectiveness of restoration efforts and tracking the numbers of wild fish over time. By estimating the numbers of hatchery and wild fish independently, the technique can help to differentiate between effects on the population due to ocean conditions and those due to freshwater conditions. That's because hatchery-raised fish don't face the same hazards in the initial freshwater phase of their life cycle that wild fish do, so they would be affected less by freshwater conditions. Not only are hatchery fish protected and artificially fed in the hatcheries, they also get a free ride downstream in tanker trucks. The hazards associated with migrating downstream to the ocean range from predators to the pumps that siphon water out of the rivers for human use.

"Most of the hatcheries in the Central Valley put the fish in tanker trucks and release them into the lower San Francisco Bay Delta, so they bypass a lot of the mortality that occurs in the rivers," Barnett-Johnson said. "If freshwater mortality was a key factor in population declines, we would expect to see hatchery and wild populations responding differently."

Barnett-Johnson plans to use the otolith technique to track changes in the composition of the salmon population over time. Unfortunately, because her research depends on a collaboration with commercial fishermen, the possible closure of the fishery this year may mean that she will not be able to get any salmon otoliths to analyze.

"At a time when we really need more information on the status of wild populations, a complete closure would mean I can't conduct my research to provide this estimate," she said.

In addition to Barnett-Johnson and Grimes, the coauthors of the paper are Chantell Royer of Humboldt State University and Christopher Donohoe of the NMFS Santa Cruz Laboratory. This research was supported by the UC Marine Council and the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO).