Chena River Chinook Salmon Study

Overview

Mystery surrounds the population of Chinook salmon (Oncorhynchus tshawytscha) inhabiting large tributaries of the Yukon and Tanana rivers in interior Alaska. A critical early part of their life history is not understood as well as it is in more accessible populations, and this may be the key to understanding the annual variability in their abundance. Our study focuses on one such population in the Chena River near Fairbanks, Alaska.

In the Chena, the adults spawn in July and August and the juveniles emerge from the gravel a couple weeks after iceout the following spring. They grow rapidly during their first summer, then overwinter in the river and head out to sea the next spring, shortly before the next year’s juveniles emerge. Most spend three to six years at sea before returning to spawn. This life history is notably different from that of many Chinook in the Yukon drainage, which migrate through the mainstem Yukon into small, non-natal streams to rear and overwinter (Bradford et al., 2001). Chinook in the Chena, as in the nearby Salcha, seem to stay within their natal river and its tributaries until smolting.

Studies of similar species suggest that populations are regulated by processes acting on the juveniles during their first summer out of the gravel. However, relatively little is known about these processes in rivers like the Chena: whether the Chinook population is limited by food, habitat, both, or neither. Our aim is to identify and understand the most important processes that limit the Chena Chinook population

We started preliminary work in summer 2007, devoting that time to preliminary abundance surveys and familiarization with relevant techniques. Our primary field seasons will be summer 2008 and summer 2009.

Project Objectives

1. Determine the timing and nature of competitive bottlenecks that might generate density-dependent mortality in juvenile Chinook salmon during the freshwater rearing period.
2. Determine the mechanisms by which stream flow and other environmental variables influence the population, with special emphasis on factors affecting the aquatic, terrestrial, and marine-derived food sources used by the juveniles.
3. Document the diel and seasonal movement patterns and habitat selection of the juveniles.
4. Characterize the effects of predation and competition on juvenile Chinook behavior and abundance, including their tendencies to gather in groups and to use large woody debris as cover.
5. Use a process-based model that incorporates behavioral and environmental data to predict how seasonal flow patterns should affect the density of juveniles at the end of summer.
6. Determine how food and temperature interact to influence growth rate and energy reserves.
7. Use a retrospective analysis to investigate the way environmental conditions influence the number of adults that return to spawn.
8. Refine the stock-recruitment analyses to account for the effects of environmental conditions on recruitment

Justification of our Project

1. Predicting salmon production and stock diversity. Our work will result in methods to predict the influence of environmental processes on productivity and returns.
2. Sustainability of salmon fisheries. Our work will improve escapement goals, forecasts, and habitat management, both important for sustainability.
3. Understanding past variations in salmon abundance. Our retrospective analysis will test hypotheses about the way environmental conditions influence abundance.
4. Evaluating management tools. We will evaluate the existing stock-recruitment analyses. We will develop assessment techniques for juvenile Chinook salmon and evaluate the resulting estimates as tools for improving stock-recruitment analysis and forecasting.
5. Habitat and juvenile survival in freshwater. We will extensively research the relationship between habitat conditions in freshwater and juvenile survival.
6. Marine-origin energy and juvenile salmon. We will evaluate the relationship between marine derived nutrients and production.
7. Spawner-recruit relationships. We will develop new analyses that incorporate the effect of environmental conditions on the spawner-recruit relationship.
8. Structure and abundance of spawning populations. Our work will provide a better understanding of the relationship between habitat conditions and abundance.
9. Advancing field techniques. Our work will require the development and refinement of techniques to study small fish in sizable rivers.
10. Advancing ecological modeling. We will advance existing models of drift-feeding salmonid habitat selection to incorporate common forces affecting aggregation and the use of cover.
    

Involved Organizations

We are funded by the Arctic-Yukon-Kuskokwim Sustainable Salmon Initiative.

Two principal investigators, all four students, and any technicians are affiliated with the University of Alaska - Fairbanks, in the Alaska Cooperative Fish and Wildlife Research Unit and the Institute of Arctic Biology. Three students are in the UAF Department of Biology and Wildlife and one is in the UAF School of Fisheries and Ocean Sciences. One principal investigator and other helpful staff work for the Alaska Department of Fish and Game.

The Tanana Chiefs Conference is also involved.

References

Bradford, M. J., Grout, J. A., & Moodle, S. (2001). Ecology of juvenile chinook salmon in a small non-natal stream of the Yukon River drainage and the role of ice conditions on their distribution and survival. Canadian Journal of Zoology, 79(11), 2043-2054.