Abstract. Alterations in variance of riverine thermal regimes have been observed and are predicted with climate change and human development. We tested whether changes in daily or seasonal thermal variability, aside from changes in mean temperature, could have biological consequences by exposing Chinook salmon (Oncorhynchus tshawytscha) eggs to eight experimental thermal regimes. Thermal variance impacted both emergence timing and development at emergence. Further, genetics influenced the magnitude of that response. Ecological implications include: (1) changes in thermal variability, independent of warming, have the potential to alter the timing of life history processes, (2) the commonly-used degree day accumulation model is not sufficient to predict how organisms respond to altered temperature regimes, and (3) there are likely to be genetic differences in how individuals and populations respond to future water temperature regimes.

A large and growing body of literature has documented the transfer of marine‐derived nutrients from the ocean to freshwater and riparian systems by semelparous Pacific salmon Oncorhynchus spp. The pathways by which these nutrients reach resident fish are often indirect, and the evidence for direct benefits to the resident fish is not always conclusive. However, the consumption of salmon tissue (in one form or another) by resident fish would constitute a direct and efficient pathway for energy transfer. We studied a population of small‐bodied, nonanadromous Dolly Varden Salvelinus malma feeding on the fry and eggs of sockeye salmon O. nerka and blowfly (family Calliphoridae) larvae that had fed on salmon carcasses at a series of spring‐fed and otherwise unproductive ponds in southwestern Alaska. The Dolly Varden fed heavily on sockeye salmon fry when available, shifted their diet almost exclusively to eggs after salmon spawning commenced, and then shifted to blowfly larvae toward the end of the season. Dolly Varden large enough to eat eggs moved into ponds where sockeye salmon spawn synchronously with the arrival of the salmon, and Dolly Varden growth rates increased greatly once salmon eggs and blowfly maggots were available. Young‐of‐the‐year Dolly Varden, which were too small to eat eggs and fry, were concentrated in small streams between ponds where fewer sockeye salmon spawn, perhaps to minimize the risk of predation from larger conspecifics. These results indicate the importance of a pulse of salmon‐related food resources for this population of resident fish and their adaptations to take advantage of these resources. It is likely that similar dependence occurs in other systems where sockeye salmon produce a suite of temporally predictable energy resources; thus, resident fish may depend on large populations of salmon.

The L(F) -at-age trajectories differentiated two populations of Dolly Varden charr Salvelinus malma and a population of Arctic charr Salvelinus alpinus from the eastern end of Iliamna Lake, Alaska. Salvelinus malma from the Pedro Bay ponds were the smallest for a given age, followed by Salvelinus alpinus from the lake, and S. malma from the Iliamna River were much larger. The utilization of a large sockeye salmon Oncorhynchus nerka subsidy by the three Salvelinus spp. populations was then investigated by comparing diet data and mixing model (MixSIR) outputs based on carbon and nitrogen stable isotopes. Stomach contents indicated that both S. malma populations fed on O. nerka products, especially eggs and larval Diptera that had scavenged O. nerka carcasses, whereas S. alpinus fed on a variety of prey items such as three-spined sticklebacks Gasterosteus aculeatus and snails. Stable-isotope analysis corroborated the diet data; the two S. malma populations incorporated more O. nerka-derived nutrients into their tissues than did S. alpinus from the lake, although all populations showed substantial utilization of O. nerka-derived resources. Salvelinus alpinus also seemed to be much more omnivorous, as shown by stable-isotope mixing models, than the S. malma populations. The dramatic differences in growth rate between the two S. malma populations, despite similar trophic patterns, indicate that other important genetic or environmental factors affect their life history, including proximate temperature controls and ultimate predation pressures.

The downstream movement of coho salmon fry and parr in the fall, as distinct from the spring migration of smolts, has been well documented across the range of the species. In many cases, these fish overwinter in freshwater, but they sometimes enter marine waters. It has long been assumed that these latter fish did not survive to return as adults and were ‘surplus’ to the stream's carrying capacity. From 2004 to 2010, we passive integrated transponder tagged 25,981 juvenile coho salmon in three streams in Washington State to determine their movement, survival and the contribution of various juvenile life histories to the adult escapement. We detected 86 returning adults, of which 32 originated from fall/winter migrants. Half of these fall/winter migrants spent ~1 year in the marine environment, while the other half spent ~2 years. In addition, the median return date for fall/winter migrants was 16 days later than spring migrants. Our results indicated that traditional methods of spring‐only smolt enumeration may underestimate juvenile survival and total smolt production, and also overestimate spring smolt‐to‐adult return (SAR). These are important considerations for coho salmon life cycle models that assume juvenile coho salmon have a fixed life history or use traditional parr‐to‐smolt and SAR rates.