MEPS 548:181-196 (2016)  -  DOI: https://doi.org/10.3354/meps11623

Isotopes and genes reveal freshwater origins of Chinook salmon Oncorhynchus tshawytscha aggregations in California’s coastal ocean

Rachel C. Johnson1,2,*, John Carlos Garza1,3, R. Bruce MacFarlane1,4, Churchill B. Grimes1,4, Corey C. Phillis5,8, Paul L. Koch6, Peter K. Weber7, Mark H. Carr2

1Fisheries Ecology Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 110 Shaffer Road, Santa Cruz, CA 95060, USA
2Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 110 Shaffer Road, Santa Cruz, CA 95060, USA
3Department of Ocean Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95060, USA
4Institute of Marine Sciences, University of California, Santa Cruz, 110 Shaffer Road, Santa Cruz, CA 95060, USA
5Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720, USA
6Department of Earth and Planetary Science, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95060, USA
7Glenn T. Seaborg Institute, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
8Present address: Metropolitan Water District of Southern California, 1121 L St. Suite 900, Sacramento, CA 95814, USA
*Corresponding author:

ABSTRACT: The ability of salmon to navigate from the ocean back to their river of origin to spawn acts to reinforce local adaptation and maintenance of unique and heritable traits among salmon populations. Here, the extent to which Chinook salmon Oncorhynchus tshawytscha from the same freshwater breeding groups associate together in the ocean at regional and smaller-scale aggregations prior to homeward migration is evaluated. Natural variation in salmon otolith daily growth bands, strontium isotopes (87Sr/86Sr), and microsatellite DNA were used as intrinsic tags to link the distributions of fish caught in the ocean with their freshwater origins. Adults were caught from vessels by hook and line in small aggregations (7-18 ind.) at the same geographic location (1-24 km of coastline) and time (4-36 h) from 3 ocean regions along central California, USA. Salmon caught together in aggregations were from the same genetic group, and to a lesser extent, of the same natal origin (individual rivers or hatcheries). However, at regional scales, adult salmon mixed. Central Valley winter-run Chinook salmon caught together in the ocean varied in the duration of freshwater rearing for up to 2-3 mo prior to seaward migration, suggesting associations within the group were not established in freshwater or maintained over the lifetime of the fish. Our findings are consistent with coarser information indicating stocks are distributed differently in time and space, but larger sample sizes are required to evaluate the consistency of patterns at smaller spatial scales. This study uncovers freshwater associations prior to homeward migration, a principle and undocumented prerequisite of the collective navigation hypothesis.


KEY WORDS: Winter-run Chinook salmon · Schooling · Otolith microchemistry · Strontium · Navigation


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Cite this article as: Johnson RC, Garza JC, MacFarlane RB, Grimes CB and others (2016) Isotopes and genes reveal freshwater origins of Chinook salmon Oncorhynchus tshawytscha aggregations in California’s coastal ocean. Mar Ecol Prog Ser 548:181-196. https://doi.org/10.3354/meps11623

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