Category: Fish/Shellfish Research
Published: January 31, 2008
Author(s): Kent Mayer, Mark Schuck and Darin Hathaway
The goal of this project is to assess the status of anadromous salmonid populations in Asotin Creek above George Creek. This research, monitoring and evaluation project provides estimates of abundance, productivity, survival rates, and temporal and spatial distribution of ESA-listed species: Summer steelhead Oncorhynchus mykiss and spring Chinook salmon O. tshawytscha. Adult salmonids entering Asotin Creek to spawn were enumerated using a floating, resistance board weir. The juvenile emigrant population was estimated using a rotary screw (smolt) trap. In 2007 (the third season of adult trapping in Asotin Creek), two hundred and ninety-four (294) adult steelhead were captured, resulting in a population estimate of 342 adults, which is a significant decrease from the previous two years. A substantially greater number of hatchery stray steelhead (17.5%) were identified this year than in previous years. There were two hundred and sixty-nine (269) redds in the 46 kilometers of spawning habitat above the adult trapping site in 2007, which generated an estimate of 0.64 females per redd. The juvenile steelhead population was estimated at 50,375 (95% CI = 43,517 â€" 59,289 juveniles) from the combined spring and fall out-migrations in 2007. Thirteen paired smolt trap efficiency tests with fin-clipped and PIT-tagged fish indicated a significant difference (p=0.048) in capture efficiencies between the two mark types. Passive integrated transponder tagging of out-migrating juvenile steelhead in 2007 indicated that only 3.1% of the age 1 fish were detected at a mainstem dam during the 2007 outmigration year, while 46.3% and 52.3% of the age 2 and age 3 fish were detected, respectively. In addition, 1,173 juvenile spring Chinook salmon were captured in 2007, resulting in a population estimate of 2,553 individuals. This report also provides a multi-year data comparison of project data collected to date: three years of adult steelhead data from 2005, 2006 and 2007, and four years of juvenile steelhead data from 2004, 2005, 2006 and 2007. These data have described a persistent steelhead population, which is variably affected by stray hatchery steelhead, but remains large for a subbasin its size when compared to other steelhead populations in the Columbia Basin. The Asotin Creek steelhead population is possibly at or above Viable Salmonid Population thresholds. These facts make it a potentially desirable control/reference stream population for evaluation of supplementation effectiveness monitoring; a critical unknown within the Columbia basin.