Masters Thesis

Residency, growth, and outmigration size of juvenile chinook salmon (Oncorhynchus tshawytscha), across rearing locations in the Shasta River, California

The Shasta River is one of the most productive tributaries of the Klamath River for Chinook salmon (Oncorhynchus tshawytscha). There are two primary spawning and juvenile rearing areas for Chinook salmon in the Shasta: the lower basin canyon, and the Shasta-Big Springs complex of the upper basin. These two areas of the basin are characterized by dramatically different in-stream habitats. This project evaluated differences in growth, residence time, and size at outmigration between these two critical salmonid habitat areas in the Shasta River using a combination of mark-recapture field studies and otolith strontium isotope ratio analysis of new and archived samples. In spring 2012 and 2013, during the primary rearing time for juvenile Chinook salmon in the Shasta River, three groups of fish were PIT tagged: (1) fish caught, tagged, and released in the upper basin; (2) fish caught at the lower basin, tagged and transplanted to the upper basin; and (3) fish caught, tagged, and released in the lower basin. Results indicate significant differences in residence time (defined as tagging date to date of outmigration), growth, and outmigration size between fish in the upper and lower basin, regardless of whether fish were originally caught in the upper basin or transplanted there. Several tagged fish residing in the Shasta-Big Springs complex displayed upstream movement and long residency times more similar to river-type Chinook salmon, than to ocean-type juveniles. Strontium isotope ratios (87Sr/86Sr) in stream water collected in March 2012 and 2013 were measured to be 0.704 (precision of 0.000031) and 0.706 (precision of 0.000019) for the upper basin and the lower basin respectively. Juvenile Chinook salmon that reared in the lower or upper basin are identifiable by the distinct differences in 87Sr/86Sr incorporated into the juvenile region of the otoliths. This creates a unique opportunity to determine the relative contribution of the two rearing areas to juvenile Chinook salmon production and, potentially, adult returns via analysis of juvenile and adult otoliths. Overall, I found consistent difference in the duration of residence, growth, and outmigration size between juvenile Chinook salmon that reared in the upper or lower Shasta River basin, irrespective of the location from which fish were initially sampled. Life history differences reflected differences in habitat conditions between the upper and lower basin. Additionally, this project demonstrated the potential use of otolith isotope analysis to identify the rearing location of juvenile Chinook salmon, which may affect marine survival and adult returns.

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