Rocky Mountain Research Station Publications

RMRS Online Publication - Journal Articles, External Publications, and Special Reports
Evaluating probability sampling strategies for estimating redd counts: an example with Chinook salmon (Oncorhynchus tshawytscha)


Courbois, Jean-Yves; Katz, Stephen L.; Isaak, Daniel J.; Steel, E. Ashley; Thurow, Russell F.; Rub, A. Michelle Wargo; Olsen, Tony; Jordan, Chris E. 2008. Evaluating probability sampling strategies for estimating redd counts: an example with Chinook salmon (Oncorhynchus tshawytscha). Canadian Journal of Fisheries and Aquatic Sciences. 65: 1814-1830.

Precise, unbiased estimates of population size are an essential tool for fisheries management. For a wide variety of salmonid fishes, redd counts from a sample of reaches are commonly used to monitor annual trends in abundance. Using a 9-year time series of georeferenced censuses of Chinook salmon (Oncorhynchus tshawytscha) redds from central Idaho, USA, we evaluated a wide range of common sampling strategies for estimating the total abundance of redds. We evaluated two sampling-unit sizes (200 and 1000 m reaches), three sample proportions (0.05, 0.10, and 0.29), and six sampling strategies (index sampling, simple random sampling, systematic sampling, stratified sampling, adaptive cluster sampling, and a spatially balanced design). We evaluated the strategies based on their accuracy (confidence interval coverage), precision (relative standard error), and cost (based on travel time). Accuracy increased with increasing number of redds, increasing sample size, and smaller sampling units. The total number of redds in the watershed and budgetary constraints influenced which strategies were most precise and effective. For years with very few redds (<0.15 redds km-1), a stratified sampling strategy and inexpensive strategies were most efficient, whereas for years with more redds (0.15-2.9 redds km-1), either of two more expensive systematic strategies were most precise.

Keywords: Chinook salmon, Oncorhynchus tshawytscha, sampling, redds


About PDFs: For best results, do not open the PDF in your Web browser. Right-click on the PDF link to download the PDF file directly to your computer. Click here for more PDF help.


Download Article
http://www.fs.fed.us/rm/pubs_other/rmrs_2008_courbois_j001.pdf

PDF File Size: 500 K


Title: RMRS Other Publications: Evaluating probability sampling strategies for estimating redd counts: an example with Chinook salmon (Oncorhynchus tshawytscha)
Electronic Publish Date: April 7, 2009
Last Update:
April 7, 2009

RMRS Publications | Order a publication | Contact Us