Cohos nearly no-shows this year
Reason for low numbers remain unclear
 |
| Issaquah Hatchery Foreman John Kugen holds an adult coho that has returned to spawn. |
This year's coho run is well below average and Department of Fish & Wildlife managers are crossing their fingers, hoping they will have enough fish to spawn to reach the program goal of obtaining 1.2 million eggs. At least 600 female are needed to reach the hatchery's goal.
The coho count passing through the Hiram M. Chittenden Locks was just 3,608 this year - well below the 30,000 annual average. Generally, about half of the total coho swimming through the Locks are bound for Issaquah. Based on the hatchery/non-hatchery returns, the Issaquah return this year could be as low as 25 percent of the coho counted at the Locks.
One fish biologist with the Muckleshoot Tribe has a theory that poor ocean conditions when the coho were smolts (the stage when juveniles migrate from fresh to salt water) resulted in lower than average survival rates for this year's fish.
The issue has to do with a change in ocean upwelling, where water from the deep sea travels up to the surface. These are places in the ocean where water from the deep sea travels up to the surface. Such upwelling often happens where wind blows along a coastline. According to Windows to the Universe, from the National Earth Science Teachers Association (NESTA), the wind causes the water at the ocean surface to move perpendicular to it, away from the coast. When surface water moves away from the coast, water from deeper in the ocean rises up and takes its place.
"The water that is moved up to the surface is usually cold and rich in nutrients, which come from the rotting bodies of dead sea creatures that sunk into deep water," Windows to the Universe reports. "When the deep water gets to the surface, these extra nutrients are snatched up by plankton that floats in the ocean. The number of plankton grows where there is upwelling. Tiny animals gobble up the plankton and fish eat the tiny animals. This means that upwelling areas are full of marine life."
In May of 2009, the National Oceanic and Atmospheric Administration did surveys in Washington marine waters and found good upwelling, said Mike Mahovlich, fish biologist with the Muckleshoot Tribe. But within a month, something changed.
"Upwelling stopped in June, continued through the summer and early fall months. The early fall test fisheries in the marine coastal waters could not find juvenile coho, which was the first sign that the 2010 adult returns could be very poor, but nobody expected it to be this bad," Mahovlich said.
More rains are predicted this weekend and Issaquah Hatchery managers hope this will bring in more coho. Meanwhile, this year's chinook spawn is complete. The hatchery collected nearly 2.5 million eggs; more than 1,000 chinook were spawned and more than 1,000 were released upstream of the hatchery.