Coordinated Monitoring Programs: Examples from the California Central Valley

Pacific salmon (Oncorhynchus spp.) often require many distinct habitats throughout their life cycles.  Therefore, impacts from various environmental parameters may have disproportionate influences on a given salmon population within and across years.  This concept has manifested into large-scale monitoring efforts throughout many watersheds of the Pacific United States to track population estimates for various freshwater life stages of salmon.  These efforts include immigrating adult passage estimates, adult carcass surveys, pre-spawn mortality estimates, redd surveys, trapping operations for fry and smolt production, various tagging methodologies and trawling efforts to estimate emigration survival from freshwater to the marine environment.  In most cases, populations of each life stage are estimated through capture-recapture models.  Fish quality (e.g. condition factor, disease) within each life stage may also be assessed as a further indicator of population response to environmental conditions.  Although methods vary, in all cases the number of salmon of a given life stage residing in or passing through a given stretch of river is estimated.  These estimates must be accurate enough not only to detect annual variation during a given life stage but also between stages to determine key parameters driving overall population variation from year to year.

Here, we consider the quantification and qualification of each life stage of an anadromous salmon population during the freshwater portion of its life cycle and the need for comparability among monitoring programs.  We then propose a modeling outline for measuring annual variation in specific life stages of a population and how well annual differences in environmental parameters and management actions explain variation in abundance estimates.  Finally, we demonstrate the approach with several case studies from the early life stages of fall-run Chinook salmon (O. tshawytscha) within the California Central Valley.