Rearing and migration of juvenile Chinook salmon (Oncorhynchus tshawytscha) in a large river floodplain

Lynn Takata,Brian M Schreier,J Louise Conrad,Ted R Sommer

doi:10.1007/s10641-017-0631-0

Abstract

Off-channel habitat has become increasingly recognized as key for migratory fishes such as juvenile Chinook salmon (Oncorhynchus tshawytscha). Hence, floodplain habitat has been identified as critical for the continued persistence of California’s Central Valley salmon, particularly the Yolo Bypass, the primary floodplain of the Sacramento River. To provide insight into factors supporting juvenile salmon use of this 240 km2, partially leveed floodplain, we examined inter- and intra-annual relationships between environmental correlates and residency time, apparent growth, emigration, migratory phenotype, and survival over more than a decade for natural-origin (“wild”) fish and experimentally-released hatchery fish. Flood duration was positively associated with hatchery juveniles residing longer and achieving larger size. Wild juveniles grew larger and emigrated later with cumulative temperature experience (accumulated thermal units) and warmer average annual temperatures during flood years. Within years, both wild and hatchery salmon departed the floodplain as flood waters receded. Parr-sized juveniles dominated outmigrant composition, though fry and smolt-sized juveniles were also consistently observed. Survival to the ocean fishery was not significantly different between hatchery fish that reared in the Yolo Bypass versus those that reared in the main stem Sacramento River. Our study indicates improved frequency and duration of connectivity between the Sacramento River and the Yolo Bypass could increase off-channel rearing opportunities that expand the life history diversity portfolio for Central Valley Chinook salmon.

Highlights

Central Valley Chinook salmon in California’s Sacramento-San Joaquin Delta (Delta) have declined precipitously in recent decades (Yoshiyama et al 2000), and their long-term persistence is uncertain (Katz et al 2013)
We examined over a decade of data on juvenile Chinook salmon survival, growth, residency, and emigration patterns in the Yolo Bypass – the largest remaining off-channel floodplain in California
Our observations from the expansive Yolo Bypass floodplain provide insight into how Chinook salmon may manage this risk in order to maximize benefits

Summary

Introduction

Central Valley Chinook salmon in California’s Sacramento-San Joaquin Delta (Delta) have declined precipitously in recent decades (Yoshiyama et al 2000), and their long-term persistence is uncertain (Katz et al 2013). Frequent and widespread flooding was once an integral part of the Delta, but the construction of dams and levees along with other activities that Breclaimed^ lowlands for agriculture and development eliminated 97% of historic wetlands (Whipple et al 2012). This dramatic landscape transformation has decimated juvenile salmon rearing habitat, resulting in reduced life history diversity (Lindley et al 2009; Waples et al 2009) and an eroded ability to buffer against variable conditions (Carlson and Satterthwaite 2011)

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Conclusion