Spatial Consistency of Chinook Salmon Redd Distribution within and among Years in the Cowlitz River, Washington

• Published in: North American journal of fisheries management 2013-06, Vol.33 (3), p.508-518
• Main Authors: Klett, Katherine J. C, Torgersen, Christian E, Henning, Julie A, Murray, Christopher J
• Format: Article
• Language: English
• Subjects: cost effectiveness; Freshwater; global positioning systems; linear models; Oncorhynchus tshawytscha; regression analysis; rivers; spatial data; spawning; surveys
• ISSN: 1548-8675; 0275-5947; 1548-8675
• DOI: 10.1080/02755947.2013.778924

We investigated the spawning patterns of Chinook Salmon Oncorhynchus tshawytscha on the lower Cowlitz River, Washington, using a unique set of fine- and coarse-scale temporal and spatial data collected during biweekly aerial surveys conducted in 1991–2009 (500 m to 28 km resolution) and 2008–2009 (100–500 m resolution). Redd locations were mapped from a helicopter during 2008 and 2009 with a hand-held GPS synchronized with in-flight audio recordings. We examined spatial patterns of Chinook Salmon redd reoccupation among and within years in relation to segment-scale geomorphic features. Chinook Salmon spawned in the same sections each year with little variation among years. On a coarse scale, 5 years (1993, 1998, 2000, 2002, and 2009) were compared for reoccupation. Redd locations were highly correlated among years. Comparisons on a fine scale (500 m) between 2008 and 2009 also revealed a high degree of consistency among redd locations. On a finer temporal scale, we observed that Chinook Salmon spawned in the same sections during the first and last week. Redds were clustered in both 2008 and 2009. Regression analysis with a generalized linear model at the 500-m scale indicated that river kilometer and channel bifurcation were positively associated with redd density, whereas sinuosity was negatively associated with redd density. Collecting data on specific redd locations with a GPS during aerial surveys was logistically feasible and cost effective and greatly enhanced the spatial precision of Chinook Salmon spawning surveys. Received August 10, 2012; accepted February 14, 2013