Retrospective patterns of differential mortality and common year-effects experienced by spring and summer chinook salmon (Oncorhynchus tshawytscha) of the Columbia River

Abstract

We used spawner-recruit data to estimate the instantaneous differential mortality (µ) experienced by seven Snake River spring and summer chinook (Oncorhynchus tshawytscha) stocks relative to six lower Columbia River stocks. We applied 37 Ricker stock-recruit models to these data, incorporating different assumptions about measurement error, transport survival, intrinsic productivity, methods of estimating µ, and common year-effects that affect the survival of all stocks. Estimates of mean µ for the 12 best models ranged from 0.55 to 1.90 (mean of 1.09), implying that passage from Lower Granite Dam to John Day Dam reduced recruitment of 1970-1990 Snake River broods by an average of 42-85% (mean of 66%). Differential mortality was cyclical and moderately high in the 1970s brood years, low for 1980-1983, near average in 1984-1989, and high in 1990. Our empirical estimates of µ showed low bias and were between those produced by two mechanistic passage models. The best empirical models included common yeareffects, which shifted from generally positive effects on 1952-1968 brood years to generally negative effects on 1970-1990 broods. Year-effects were not significantly correlated with two climate indices or with water travel time (the time that water takes to travel down the Columbia River).

A Multiple Watershed Approach to Assessing the Effects of Habitat Restoration Actions on Anadromous and Resident Fish Populations, Technical Report 2003-2004.

“…A positive change in historical salmonid productivity in the Yakima Subbasin that differs significantly over time from the patterns demonstrated by control watersheds would indicate a detectable and beneficial effect of the screening actions. T o isolate the possible effects of fish screening on overall productivity we first developed a series of log-linear regression models explaining the spawner and recruitment data for spring chinook (salmon species with the most complete historical time series for the Yakima and control subbasins and largest spatial distribution) based on Ricker-type-stock-recruitment relationships and a range of potential environmental covariates that might partially explain any observed trends in fish survival data (as in Deriso et al 2001; Thompson and Lee 1999). We then developed an index of fish screening related survival that could be included as a time-dependent term in each of our regression models.…”

“…By accounting for common sources of variation we hoped to increase our power to detect streamspecific habitat effects. Similar models have been applied to spawner-recruit and parr-to-smolt survival data (e.g., Deriso et al 2001, Paulsen and Fisher 2003), but to our knowledge this is the first time they have been applied to egg-to-parr survival data. We implemented the common year effect in two ways: (1) by estimating it from the data (BY t in Eq.…”

“…Similar to Model 1, but ocean productivity indicators are replaced by a measure of common years, δ t , (as in Deriso et al 2001). Each brood year's δ t reflects relative changes in ln(R/S) that are common across all stocks in a given year; the mean value of δ t across all years is zero.…”

“…We did so because this approach gives a formal accounting of the relative plausibility of the estimated models. Deriso et al (2001) and T hompson and Lee (2002) have applied similar information-theoretic approaches to chinook spawner-recruit models, while Paulsen and Fisher (in review) have used this approach to explore habitat factors affecting survival of juvenile chinook.…”

Testing for delayed mortality effects in the early marine life history of Columbia River Basin yearling Chinook salmon

“…Thus, the lower productivity of the Snake River population was attributed to their exposure to first the 4 lower Snake River dams in addition to the 4 lower Columbia River dams which make up the Federal Columbia River Hydro power System (FCRPS or 'hydrosystem'; Fig. 1; Schaller et al 1999, Deriso et al 2001, Wilson 2003.…”