Skip to main content

Vertical self-sorting behavior in juvenile Chinook salmon (Oncorhynchus tshawytscha): evidence for family differences and variation in growth and morphology


Life history variation is fundamental to the evolution of Pacific salmon and their persistence under variable conditions. We discovered that Chinook salmon sort themselves into surface- and bottom-oriented groups in tanks within days after exogenous feeding. We hypothesised that this behaviour is correlated with subsequent differences in body morphology and growth (as measured by final length and mass) observed later in life. We found consistent morphological differences between surface and bottom phenotypes. Furthermore, we found that surface and bottom orientation within each group is maintained for at least one year after the phenotypes were separated. These surface and bottom phenotypes are expressed across genetic stocks, brood years, and laboratories and we show that the proportion of surface- and bottom-oriented offspring also differed among families. Importantly, feed delivery location did not affect morphology or growth, and the surface fish were longer than bottom fish at the end of the rearing experiment. The body shape of the former correlates with wild individuals that rear in mainstem habitats and migrate in the fall as subyearlings and the latter resemble those that remain in the upper tributaries and migrate as yearling spring migrants. Our findings suggest that early self-sorting behaviour may have a genetic basis and be correlated with other phenotypic traits that are important indicators for juvenile migration timing.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6


Download references


We thank R. Couture and J. O’Neil for rearing fish for these experiments and construction of behavioural observation facilities. O. Hakanson, C. Danley, K. Self and H. Stewart assisted with sampling and data collection. L. Ciannelli and others provided constructive comments on earlier drafts of this manuscript. The US Army Corps of Engineers, Portland District provided funding for this research (Project TD-13-02). Additional support was provided by the USGS, the Oregon Department of Fish and Wildlife and the Oregon Hatchery Research Center. Animal rearing, behaviour experiments and morphometric procedures were approved by the Institutional Animal Care and Use Committee at Oregon State University (ACUP #4289).

Author information

Authors and Affiliations


Corresponding author

Correspondence to Julia R. Unrein.

Ethics declarations


Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

This draft manuscript is distributed solely for purposes of scientific peer review. Its content is deliberative and predecisional, so it must not be disclosed or released by reviewers. Because the manuscript has not yet been approved for publication by the U.S. Geological Survey (USGS), it does not represent any official USGS finding or policy.

Electronic supplementary material


(DOCX 737 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Unrein, J.R., Billman, E.J., Cogliati, K.M. et al. Vertical self-sorting behavior in juvenile Chinook salmon (Oncorhynchus tshawytscha): evidence for family differences and variation in growth and morphology. Environ Biol Fish 101, 341–353 (2018).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


  • Life history variation
  • Geometric morphometrics
  • Phenotype
  • Genetics