Spring outmigration of wild and hatchery chinook salmon and steelhead trout smolts from the Imnaha River, Oregon, February 6, 1995-June 20, 1995

摘要

For the second consecutive year, the Nez Perce Tribe, in conjunction with the Fish Passage Center, participated in the smolt monitoring program in the Imnaha River. A rotary screw trap was used to collect emigrating wild and hatchery chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) smolts from February 6 to June 20, 1995. We PIT tagged and released 421 wild chinook salmon smolts, 747 hatchery chinook salmon smolts (445 HxW and 302 HxH), 227 wild steelhead trout smolts and 1,296 hatchery steelhead trout smolts. Cumulative interrogation rates at mainstem Snake and Columbia River dams were 78.4% for wild chinook salmon, 58.9% for hatchery chinook salmon (HxW), 56.6% for hatchery chinook salmon (HxH), 76.2% for wild steelhead trout, and 69.2% for hatchery steelhead trout. Peak outmigration of NPT tagged wild Imnaha River chinook salmon smolts occurred from early to mid-May at Lower Granite, Little Goose, and Lower Monumental Dams. Median and 90% passage dates for wild chinook salmon smolts at Lower Granite Dam were May 1 and May 11, respectively. Continuous spill at Lower Granite Dam was initiated on May 3 and lasted for 51 days. The 90% passage date of wild chinook salmon smolts at Lower Granite Dam (May 11) preceded peak Snake River and Lower Granite (June 6) flows by 26 days. Although hatchery chinook salmon exhibited a shorter outmigration period through the Snake River than their wild counterparts, peak arrival for both groups occurred at approximately the same time. Median and 90% passage dates at Lower Granite Dam for other PIT tagged groups were: hatchery chinook salmon (NPT-HxW) - May 2 and May 13; hatchery chinook salmon (FPC-HxH) - May 8 and May 15; wild steelhead trout - May 2 and May 9; and hatchery steelhead trout (NPT and FPC) - May 31 and June 16. Hatchery steelhead trout displayed small peaks in arrival timing at Lower Granite and Little Goose Dams in mid-May to mid-June.