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The abundance of many Chinook salmon ( Oncorhynchus tshawytscha) stocks has declined despite reductions in harvest. We used state-space models parameterized with data from 57 Chinook salmon indicator stocks, ranging from coastal Oregon to southeast Alaska, to quantify long-term (since 1972 release year) changes in juvenile marine survival rate and mean age-at-maturity, as well as identify stock groupings with coherent dynamics. We found that juvenile marine distribution—rather than freshwater life history, run timing, or adult marine distribution—was the best predictor of trends in both survival and age. Only subyearling stocks that enter the Strait of Georgia showed evidence of transitioning to a low juvenile survival period, other groupings exhibited low and stable or cyclical patterns in survival. Conversely, declines in mean age-at-maturity were widespread and do not appear to have stabilized, suggesting that future declines in Chinook salmon population productivity may be influenced by earlier maturation or increased adult mortality, rather than further reductions in juvenile marine survival.

Recruitment variability in many fish populations is postulated to be influenced by climatic and oceanographic variability. However, a mechanistic understanding of the influence of specific variables on recruitment is generally lacking. Feeding ecology is one possible mechanism that more directly links ocean conditions and recruitment. We test this mechanism using juvenile Chinook Salmon (Oncorhynchus tshawytscha) collected off the west coast of Vancouver Island, British Columbia, Canada, in 2000–2009. Stable isotopes of carbon (δ13C), an indicator of temperature or primary productivity, and nitrogen (δ15N), an indicator of trophic position, were taken from muscle tissues of genetically stock-identified salmon. We also collated large-scale climate indices (e.g., Pacific Decadal Oscillation, North Pacific Gyre Oscillation), local climate variables (e.g., sea surface temperature) and copepod community composition across these years. We used a Bayesian network to determine how ocean conditions influenced feeding ecology, and subsequent survival rates. We found that smolt survival of Chinook Salmon is predicted by their δ13C value, but not their δ15N. In turn, large-scale climate variability determined the δ13C values of salmon, thus linking climate to survival through feeding ecology, likely through qualities propagated from the base of the food chain.

Two distinct populations of resident killer whales (Orcinus orca) in the north-eastern Pacific Ocean have been listed in Canada and the USA as being of conservation concern. One of the major threats recognized for these two populations is nutritional stress associated with prey abundance levels and availability. The predominance of chinook salmon (Oncorhynchus tshawytscha) in the summer diets of both killer whale populations has been shown by recent studies, and correlations between indices of chinook salmon abundance and resident killer whale (RKW) vital rates have generated hypotheses about the potential for chinook salmon abundance to limit RKW population dynamics. This study merges statistical inference derived from linkages between RKW vital rates (survival probability and fecundity rates) and chinook salmon abundance with demographic perturbation analysis and population viability analysis to address some of the pressing questions that have recently engaged the efforts of scientists and managers interested in: (1) the role of chinook salmon abundance in the population dynamics of RKW; and (2) how RKW population viability is expected to respond to changes in chinook mortality owing to harvest. Numerous interactions between the abundance of chinook salmon aggregates and RKW vital rates were found and deemed to result from predator–prey dynamics. However, the results of this present analysis also indicated that the effects of these interactions on RKW population growth and viability are relatively small and/or uncertain and in need of further research. Other factors (genetic, environmental and/or anthropogenic) could be at play limiting RKW population growth and possibly masking and confounding the detection of stronger interactions between RKW vital rates and chinook salmon abundance. Given the current state of information, it is highly uncertain whether the allocation of chinook salmon resources for RKW would be an effective management action in RKW recovery plans. © 2014 Her Majesty the Queen in Right of Canada. Aquatic Conservation: Marine and Freshwater Ecosystems © 2014 John Wiley & Sons, Ltd.

Conservation concerns for small, relatively unproductive populations of Chinook salmon Oncorhynchus tshawytscha limit the utility of fisheries in Canada's Fraser River. To identify population-specific migration time and to index abundance, we analyzed 4,822 fish sampled for genetic variation in 2000 and 2001 and 580 fish with coded wire tags (CWTs) caught from 1987 to 2004 in a test fishery near the river mouth. Population sizes estimated from microsatellite variation were within 3.4% of the known-origin population composition and were unbiased in comparison with known-origin population sizes. All but 1 of the 30 populations detected by both genetic methods and CWTs had overlapping migration times, but these times differed significantly for only 7 populations. Migration times were identified for another 23 untagged populations identified by using genetics, which resulted in the assignment of migration timing groups (peak passage) for 53 populations as spring (March–May), early summer (June), mids...

Uncertainty can be incorporated into area-under-the-curve (AUC) and peak count estimates of salmon escapement by conducting replicate fish counts and developing independent escapement estimates over several years. We describe a bootstrap procedure that follows the trapezoidal AUC method and incorporates the uncertainty associated with fish counts, the shape of the spawner curve, observer efficiency, and residence time. However, the procedure does not incorporate all sources of uncertainty or address the problems posed by sparse surveys or nonzero first or last counts. For the peak count method, the procedure was modified to include the uncertainty from fish counts, observer efficiency, the expansion factor, and the timing of scheduled flights with respect to peak spawning activity. Data from spring-run, stream-type chinook salmon Oncorhynchus tshawytscha in the Nicola River, British Columbia, were used to demonstrate the procedures' applications. Replicate aerial spawner counts were similar and r...

From July to October 1994 and 1995, the food habits of walleye Stizostedion vitreum, sauger S. canadense, northern pike Esox lucius, and channel catfish Ictalurus punctatus were studied in Lake Sakakawea, a Missouri River main-stem reservoir in North Dakota. In 1994, no paddlefish Polyodon spathula were found in stomachs of these predators. In 1995, 3% of the walleyes, 12% of the saugers, and 1% of the channel catfish with identifiable prey ate wild age-0 paddlefish. Walleyes ate paddlefish from August to October, with the highest proportions in September, whereas saugers ate paddlefish from July to October in equal proportions. Walleye and sauger stomachs contained wild age-0 paddlefish as large as 167 mm body length (BL; 305 mm total length, TL), and one channel catfish stomach contained a 142-mm-BL (269-mm-TL) paddlefish. Predators were also sampled after 8,000 hatchery-reared, age-0 paddlefish (mean BL = 189 mm) were released in White Earth Bay, Lake Sakakawea. Hatchery-reared paddlefish were...