on the cover / By Natalie Arroyo

Last Call for Coho

An iconic species on the brink in the Mattole Valley and beyond

(July 7, 2011)  Scores of young fish gleam like sparkling confetti as they swirl around in a submerged metal box. Volunteers and employees of the nonprofit Mattole Salmon Group are tallying fish as they migrate from the Mattole River’s headwaters toward the ocean. The workers briefly trap a percentage of the young fish, count and measure them, then release them back to the river.

Juvenile salmonids — the family of fish that includes salmon and trout — are counted in several ways by scientists. The resulting data is used to analyze the specie’s health and understand its habitat needs. Fisheries scientists and volunteers in the Mattole River and throughout the world use the figures from these fish counts as guideposts for action. When the numbers rapidly decline, for one reason or another, experts and activists set about making plans to revive the population and improve its chances for survival.

A coho salmon carcass observed during a spawner survey, in which dead adult fish and salmon nests, or redds, are assessed. PHOTO COURTESY OF BOB PAGLIUCO

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Like the young of any species, the little migrating fish observed during spring and summer monitoring efforts are vulnerable to many predators and pitfalls. Even in optimal conditions, a relatively small percentage return as adults to spawn in their home streams. Still, monitoring adult salmon returns can serve the same purpose as the proverbial canary in the coal mine: When salmon numbers dwindle, it suggests a serious imbalance in the ecosystem.

Such is the case on the North Coast. The numbers of coho salmon in river systems throughout our region have plummeted. In the past two years, scientists studying the Mattole River have seen the largest decreases ever recorded.

“Historically, the Mattole coho population was estimated to be 20,000 adults per year,” said Keytra Meyer, the Mattole Salmon Group’s executive director. Scientists last year counted just three adult coho and two underwater egg nests, called “redds.”

“The 2009-10 run was the lowest we’ve seen in 30 years of surveys,” Meyer said.

This year’s numbers were a slight improvement — 10 adults and five redds. But that doesn’t necessarily indicate better conditions in the river system. Each group — or “cohort” — of Mattole salmon takes three years to complete its life cycle, from birth through growth in the ocean and finally the return to freshwater to spawn. Since 2002, Meyer said, cohort numbers have decreased drastically. The 2009-10 returns, for example, represented a 95 percent drop from 2006-07. This year’s decrease was similar.

The Mattole River travels a remote 62-mile stretch from its headwaters in northern Mendocino County through the tiny Humboldt County towns of Whitethorn, Honeydew and Petrolia before meeting the Pacific near the westernmost point of the continental United States. To most, the Mattole seems relatively pristine, a little pocket of paradise. Its remoteness has been its salvation in many respects: fishing in this un-dammed river is limited to catch-and-release, and it has experienced minimal genetic influence of fish transplanted from other rivers.

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