Species of Concern: Hatchery Strays and Natural Production Coastal CutthroatTule Fall Chinook Winter SteelheadCoho Salmon
Grist Mill Site River Mile 2.5 Fishway constructed in 1958 Adult trap operated since 1999 Smolt Trap operated since 1998
Smolt Monitoring Goals Unbiased estimates of coho, steelhead, & cutthroat smolt yield (CV < 10%). Estimates of juvenile Chinook outmigrants if funding is available Contribution of coho from a remote site incubator program is based on otolith marks. CWT natural origin coho to estimate marine survival and fishery contributions
Cedar Creek Adult Monitoring Goals & Methods Estimate the abundance, age, & origin for Tule Fall Chinook, coho, and winter steelhead populations BioSample all adult salmonids trapped at the fishway (River Mile 2.5) Tag all fish captured in the fishway for mark- recapture abundance estimates Monitor Petersen assumptions needed for an unbiased estimate Recover adult salmonids through a variety of methods
Recapture Events Recapture event is a combination of carcass recoveries (salmon), along with hoop trap & resistance board weir recoveries (4 miles upstream of the fishway) Recover steelhead kelts in the screw trap & through seining above the resistance board weir Estimate trap efficiency for steelhead –Trapped fish are tagged and released below the fishway –Enumerate number of steelhead that successfully re-ascend the fishway –Estimate the proportion fish using the ladder
2001-03 Hoop Trap Pre High Water EventPost High Water Event limited success at recapturing coho and steelhead due to trap avoidance and large debris loads
Mark-recapture statistics & summary for unmarked adult coho salmon and winter steelhead
Maximum Likelihood Estimates trap efficiency % fish using ladder binomial distribution skewed or long tailed imprecise estimates Maximum Likelihood Estimates Abundance binomial approximation to hypergeometric distribution skewed or long tailed very imprecise estimates
Rivot, E., and E. Prevost. 2002. Hierarchical Bayesian analysis of capture- mark-recapture data. Can. J. Fish. Aquat. Sci. 53:2157-2165. Application of Rivot et al. 2002 to Cedar Creek adult steelhead estimate Posterior probability = prior X likelihood Non-informative priors & hyperpriors (hierarchical models) – priors have little influence on posterior probabilities Common distributions for trap efficiency & population estimate are the beta and normal probability distributions, respectively Other distributions could be used
Hierarchical Modeling all annual trap efficiencies come from a common distribution of trap efficiencies and their ordering does not affect the model (exchangeable) borrow strength from other trap efficiencies because they are similar Hierarchical Modeling shrink estimates toward the mean, which yields improved precision can be used for both trap efficiency & population abundance compromise between individual and fully pooled estimates
Summary Annual steelhead smolt estimates are an order of magnitude lower than coho. Mean steelhead smolts are 2,900 compared to 38,000 for coho salmon. Our adult steelhead estimates are also an order of magnitude lower than coho. For example, in 2009 the steelhead abundance was 200 fish compared to 2,200 for coho. Cedar Cr. Steelhead program should be designed to provide more precise abundance estimates. Hierarchical approach is a good approach when dealing with sparse data and common distributions.
Cedar Creek Adult Steelhead Recommendations Mark all wild steelhead captured at the fishway trap. Release all marked steelhead below the fishway trap to estimate ladder use. The recapture events should be designed to obtain at least 10 recaptures through the resistance board weir, seining and the screw trap catch of kelts. If recaptures are sparse, recaptures can be supplemented through snorkeling.