Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7591
Title: Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss):  a review of the processes and patterns
Author: N. Kendall, John R. McMillan, Matthew R. Sloat, T. W. Buehrens, T. P. Quinn, G. R. Pess, K. V. Kuzischchin, Michelle M. McClure, Richard W. Zabel
Publication Year: 2015
Journal: Canadian Journal of Fisheries and Aquatic Sciences
Volume: 72
Issue: 3
Pages: 319-342
Keywords: Oncorhynchus mykiss, anadromy, residency, Genetics, environment, conditional strategy,

Partial migration, where a fraction of individuals in a population exhibit anadromy and another fraction remain as residents in freshwater, is a common phenomenon in Oncorhynchus mykiss throughout their range across the Pacific Rim. Many populations of anadromous O. mykiss are threatened, and recovery efforts have generated increased interest in understanding the processes shaping anadromy and residency to help evaluate how populations might respond to restoration actions and climate change. In this paper we review and synthesized the published literature on the patterns of and processes influencing anadromy and residency in O. mykiss to provide context for existing information and suggest next steps for future studies. Our review indicates that anadromy and residency in O. mykiss are the product of an interaction among genetics, individual condition, and environment. As with many salmonines and in support of the conditional strategy theory, where individuals adopt a life history strategy based on their conditional status relative to a genetic threshold, there was clear evidence of a proximate influence of individual condition on anadromy and residency. Individual condition also appeared to interact with the ultimate effects of size and age at maturity and iteroparity. Thus, while life history strategy is influenced to a large degree by genetics, individuals can exhibit plasticity under variable environmental conditions. We found evidence of differences among anadromous and resident individuals in gene expression related to traits such as growth, smolt transformation, and metabolism. In addition, except for a generally positive association between whole body lipids and residency, we discovered that effects of fish body size and growth on anadromy and residency were not always consistent. Finally, patterns in anadromy and residency among and within populations suggested a wide range of possible environmental influences at different life stages including water temperature, food supply, stream flow, river geomorphology and the presence of lakes, density dependence, the cost of migration to and from the ocean, and marine survival. Although there were a number of interesting correlations between environmental conditions and life history strategy, direct tests of mechanisms were scare and there is little empirical data on the extent of residency and anadromy. Consequently, we identified as many data gaps as conclusions, leaving ample room for important future resarch on these diverse and fascinating fish.


A review paper on anadromy and residency in Oncorhynchus mykiss

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Theme: Recovery and rebuilding of marine and coastal species
Foci: Describe the relationships between human activities and species recovery, rebuilding and sustainability.
Characterize the population biology of species, and develop and improve methods for predicting the status of populations.