Gnat Creek Oxygen Supplementation

The Gnat Creek Hatchery near Knappa, Oregon produces a little less than a million spring Chinook pre-smolts each year for placement into estuary net pens operated by Clatsop County Fisheries. This is part of the Select Area Fisheries Project, a collaborative inter-governmental fish-for-harvest program that provide coho, spring and fall Chinook for harvest as a mitigation for the impact of hydroelectric dam operation on the Columbia River.

Willamette River hatchery spring Chinook eyed eggs are trucked to Gnat Creek each fall where they are incubated and reared until the following fall when they are trucked to three net pen sites in the Lower Columbia River estuary. Ideal time of entry is in mid to late November when the water temperatures in the estuary are below 55 F.

Unfortunately, Gnat Creek often would reach too warm of temperatures and flows would decrease to the point that pre-smolts would have to be transferred in September or October. Fish would be stressed and the estuary would harbor many disease vectors that would result in frequent epizotics. The cost of medicated feeding was considerable and SARs was a fraction of what it should have been.

The collaboration between what would become two Redd Zone staff members, set out to demonstrate the efficacy of oxygenating the one hundred foot raceways so that fish cold be held until November regardless of stream flows.

A demonstration project using liquid bottled oxygen funded by Clatsop County Fisheries was successful at which point a grant for installing oxygen in all fifteen raceways was submitted to the Oregon Restoration and Enhancement Board. This was successful and now all the springers produced are healthier and are held at the facility until mid-November obviating the need for medicating the fish.

Adult returns may be well above previous achievements if the first recruitment class is and indicator. In 2010 harvest of spring Chinook in Youngs Bay and the other Select areas in Oregon were five times their normal. Once again, it appears healthy fish survive better.