By Roger Sideman
Sentinel staff writer
February 26, 2007
DAVENPORT – One lone female coho salmon made the journey home to Scott Creek this year to spawn – not good news for a fish that desperately needs some.
Salmon researchers had expected 10 to 25 silvery-red females to return and lay eggs this year at the creek, a habitat that typically hosts more coho than neighboring streams and is considered to be a good barometer for species health in half a dozen other waterways between Santa Cruz and Half Moon Bay. As many as 100 male coho were also expected to return, but none appeared in the early part of January when the majority of each year’s run comes home.
Since females return every three years to spawn – at the end of their life-cycle – this year’s absence signifies the possible extinction of one-third of the wild coho that belong to Scott Creek.
That’s a significant blow for a creek that once was home to hundreds of the fish, scientists say.
They say that without a successful transplanting of hatchery-raised coho, or the arrival of more wild fish in 2008 and 2009, the coastal creeks that still support them could become barren like the San Lorenzo River, which they believe lost its native coho population long ago.
“It’s horrible,” said Sean Hayes of the salmon ecology team at the National Oceanic and Atmospheric Administration Fisheries lab in Santa Cruz.
Scientists say it is unclear whether the low numbers at Scott Creek are part of a larger phenomenon, as reports of coho returns from hatcheries up the California coast are mixed this winter.
The lone mother in Scott Creek was trapped and taken to a Davenport hatchery operated by the Monterey Bay Salmon and Trout Project, where she laid eggs and was given a name, PW-1063.
Scientists will trace her ancestry by analyzing tissue samples. These genetic portraits are frequently taken to help determine whether offspring will survive in neighboring streams and whether the overall genetic diversity of the coho species has declined. Its offspring, raised in captivity, will be tagged to monitor their endurance in the wild.
Coho were once prevalent in coastal streams stretching from Santa Cruz County to Alaska. Now, California’s coho numbers have plummeted to 1 percent of its historic population, according to fishery biologists. The local restoration effort began in the early 1980s with the Davenport hatchery.
“We thought they were on their way to recovery until El Niño in 1998, and would’ve recovered since then, but it has now taken a big hit,” Hayes said.
Unless “a last-ditch emergency effort” using artificial propagation is successful, the coho may never fully recover, experts said.
Because the coho population is so small, they are especially vulnerable to subtle changes in their environment.
The culprit behind this winter’s dismal coho turnout, they say, is weak rainfall. Low flows prevented creek mouths from opening in time for the fish to return to their native streams.
“They were sitting around at the river mouth, waiting for it to rain,” said Dave Streig, hatchery manager for the nonprofit Monterey Bay Salmon and Trout Project.
The fish died waiting, or may have strayed into neighboring streams.
Some scientists believe that the local coho’s problems began in the mid-1800s after a wave of post-Gold Rush settlers and new canneries overfished local streams to the point of extinction.
“Droughts and floods have hammered the coho,” he said.
The fish are also sensitive to changes in the ocean’s temperature, predation and inbreeding.
Other factors that have historically contributed to the coho’s decline include logging, gravel mining and road building.
For the past 20 years, members of the Salmon and Trout Project have been volunteering to catch adult steelhead and coho salmon to send to a nearby hatchery to reproduce.
This spring, they will release roughly 2,300 hatchery-bred juvenile coho into Scott Creek. Next year, they hope to release up to 6,000.
Coho salmon south of San Francisco Bay have been on the state’s endangered species list since 1995. The federal government has listed them as threatened in the Central Valley since 1996 and in Northern California since 1997.
The state’s coho have declined significantly in the past half-century. Previous studies found a decline of at least 70 percent since the 1960s.
Contact Roger Sideman at email@example.com.
- Coho salmon are a threatened species under federal law and endangered under state law.
- Coho differ from other salmon and steelhead trout in that they stay in freshwater for about 18 months. But chinook, for example, head to sea in their first summer of life.
- The fish typically spend two years in the sea, though some males return to streams after only one season in the ocean.
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