Planning to enjoy some wine this weekend? If so, consider a toast to Northern California's salmon. The two - wine and salmon - look to be linked in a way far removed from the usual pairing of one with the other at the table.
Salmon that migrate up the North State's rivers are contributing to the health of vineyards by boosting the nitrogen content of vines, suggests a study by Joseph Merz, a Lodi fisheries biologist, and Peter Moyle, a professor of fish biology at UC Davis.
Here's what they found: After salmon spawn at the end of their run, they die. Scavengers, such as turkey vultures, river otters, coyotes, raccoons and rats, snag and devour the dead salmon. As carcass or waste, the remains of the salmon often are left in vineyards and other fields along North State rivers.
These remains contain nitrogen that enrich the soil. "Around 20 percent of the nitrogen in the vegetation along a river is from a marine source, most likely salmon," Merz says.
Merz and Moyle studied the nitrogen content of vegetation along the Mokelumne and Calaveras rivers, finding more nitrogen from a marine source along the Mokelumne than the Calaveras, probably because the salmon run in the Calaveras isn't as consistent as it is in the Mokelumne, Merz says.
While in the Pacific Ocean, chinook salmon absorb nitrogen, along with phosphorus, carbon and other nutrients. This marine nitrogen is somewhat heavier than other nitrogen. This is how the biologists could track it from fish to field. Farmers tending the vineyards where the two took samples of grape leaves hadn't been using nitrogen fertilizer from a marine source, Merz says.
One practical aspect of the study, funded by the East Bay Municipal Utility District, is that farmers along rivers with robust salmon runs theoretically could reduce the amount of nitrogen fertilizer they use.
More to the point, says Merz, the study shows the interconnectedness of the environment in general and the value of the North State's salmon run in particular.
"Salmon are providing essential nutrients for grape growing and wine production. It's an ecological service for free," Merz says. "We often hear that if we protect the salmon, something else will be hurt, but when we have healthy rivers and salmon, it isn't just the fishermen who benefit; farmers benefit, the quality of life benefts."
Whether salmon and their nitrogen affect the nature and quality of the resulting wine is unknown. While Merz acknowledges that some aspects of the two-year study were based on assumptions, the results have been published as "Salmon, Wildlife, and Wine: Marine-Derived Nutrients in Human-Dominated Ecosystems of Central California" in the journal Ecological Applications.
This weekend's toast need not be as long as that title. Just take a sip and thank the salmon that may have played a role in its development. The turkey vulture, river otter, raccoon or rat, too.