Spawning Distribution of Fall Chinook Salmon in the Snake River : Annual Report 1998
In 1999, we collected data on the spawning distribution of hatchery fall chinook salmon that were released upriver of Lower Granite Dam. Yearling fish were released at three locations that were phased in over a three-year period. Multiple release sites were used with the intent to distribute spawning throughout the existing habitat, and our project was designed to determine if this actually occurred. We first trapped returning fish at Lower Granite Dam, identified their origin (all fish were
... ernally marked), and used radio-tags to follow the fish to where they spawned. The initial plan was to tag and track about 50 returning adult females from each release site over a five-year period, 1998-2002. In the course of our work, however, we found that we could not track about 30% of the fish that we tagged. As a result, we increased the tagging target to 90 fish per release site. Mostly female fish were targeted so that we could determine spawning locations by observing redds, although some male fish (adults and one-ocean males) were also targeted to obtain information on the movements of both sexes and all age groups. In addition, returns from subyearling hatchery fish released (and PIT-tagged natural fish) upriver of Lower Granite Dam were targeted for radio-tagging to augment the project. In 1999, a total of 73 fall chinook salmon were radio-tagged, and tagging and tracking proceeded as planned. The data collected during the 1999 field season is being processed and a preliminary analysis will be included in upcoming reports. A preliminary analysis of the data collected in 1998 showed that roughly 80% of the yearling fish released at Pittsburg Landing spawned in the upper half of the Hells Canyon Reach. This suggests the release strategy may produce the desired spawning distribution for this release site. The same cannot yet be said for the other sites. Preliminary data from the Captain John site shows adult fish from subyearling releases entered the Grande Ronde River, whereas returns from yearling and subyearling releases at the Pittsburg Landing site did not.