Evaluating probability sampling strategies for estimating redd counts: an example with Chinook salmon (Oncorhynchus tshawytscha)

• Published in: Canadian journal of fisheries and aquatic sciences Vol. 65; no. 9; pp. 1814 - 1830
• Main Authors: Courbois, Jean-Yves, Katz, Stephen L, Isaak, Daniel J, Steel, E. Ashley, Thurow, Russell F, Wargo Rub, A. Michelle, Olsen, Tony, Jordan, Chris E
• Format: Journal Article
• Language: English
• Published: Ottawa, ON National Research Council of Canada 01.09.2008; NRC Research Press; Canadian Science Publishing NRC Research Press
• Subjects: Agnatha. Pisces; Animal populations; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Combinatorial probabilities; Estimating techniques; Evaluation; Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.); Fish populations; Fisheries; Fishery management; Freshwater; Fundamental and applied biological sciences. Psychology; Geometric probabilities; Management; Methods; Oncorhynchus tshawytscha; Population density; Probabilities; Probability; Salmon; Salmon fisheries; Statistical sampling; Stratified sampling; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; United States; North America; Idaho; America; Canada; USA, Idaho; Salmonidae; Oncorhynchus tshawytscha; Plane; Taxonomy; Diversity; Time series; Abundance; Fishing; Breeding site; Confidence interval; Vertebrata; Accuracy; Pisces; Strategy; Stream; Sampling; Inventory
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/F08-092

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.