Abstract
We report the geographic distribution and the densities and catch rates of Chinook salmon fry, Oncorhynchus tshawytscha, in different substrata and nearshore zones in the northwestern SacramentoSan Joaquin Delta of the San Francisco Estuary, California, USA. Nearshore zones in the freshwater, tidally influenced northwestern delta are dominated by riprap, and contain sparse sections of tule beds, beaches, and riparian zones. We sampled at six beach seine sites and eight electrofishing sites during winter 2001 along the Sacramento River,
Highlights
Many estuaries have been shown to provide important nursery habitat for salmon fry, especially Chinook salmon, Oncorhynchus tshawytscha. (Reimers 1971; Levy and Northcote 1981; Healey 1980, 1991)
Fry densities were higher in beach substrata than in riprap substrata (MLR, LR test, P < 0.005), in the Sacramento River and Steamboat Slough (Figure 2)
The Sacramento River is a major downstream migration route for Chinook salmon fry, none were found in Sacramento River riprap
Summary
Many estuaries have been shown to provide important nursery habitat for salmon fry, especially Chinook salmon, Oncorhynchus tshawytscha. (Reimers 1971; Levy and Northcote 1981; Healey 1980, 1991). California's Sacramento-San Joaquin Delta (Figure 1) is a highly modified estuary and its importance as a nursery habitat for Chinook salmon fry has not been well san francisco estuary & watershed science studied. Our goal in this study was to describe the geographic distribution and to compare the densities of Chinook salmon fry in different habitats and nearshore zones in the northwest delta during winter 2001. The northwest delta consists of sloughs, channels, and flooded islands Water circulation in these habitats is influenced by both tides and Sacramento River Basin outflow. Portions of the Yolo Bypass that are flooded in winter and early spring provide spawning and nursery habitat for Chinook salmon and many other species (Sommer and others 2001a, 2001b, 2005). The effects of such flooding on juvenile salmon distribution and abundance have not been reported
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