Masters Thesis

Run timing, fat content and maturity of spring- and fall-run Klamath River chinook salmon (Oncorhynchus tshawytscha)

Genetic stock identification methods revealed consistent stock-specific run timing of four genetically-assigned reporting groups of Klamath Basin Chinook salmon across two sampling years. The Trinity-Salmon Spring run entered first, followed by the Klamath Fall run, then the Lower Basin Fall run. The Trinity-Salmon Fall run entered throughout the six month return season. The Trinity-Salmon Spring run, by entering as early as May, reside in freshwater up to four months prior to spawning, as opposed to as little as one month for their fall-run counterparts and thus, have higher metabolic demands during their spawning migration. Accordingly, upon freshwater entry, the earlier returning fish had the greater fat reserves (estimated by non-water tissue fraction and condition index). They also arrive less mature (as estimated by total gonad mass and mean egg size), which also places greater demands on their energy reserves for gonadal development in freshwater compared to later arrivals. Weekly sampling over the entire season revealed a gradual decrease in fat reserves and a reciprocal increase in maturity as the season progressed. At spawning, the Trinity River Hatchery spring- and fall-run fish, after travelling the same distance, had the same size-specific mean egg mass and fecundity. However, fat depletion was greater in spring-run fish, highlighting their increased energy demands. The cost associated with the early entry of spring-run fish, and resulting reduced at-sea feeding period, appears to be a smaller body size at maturity for a given age. This study demonstrated that imminent freshwater residency duration is likely important in determining fat content and maturity level of Chinook salmon upon entering a freshwater system to spawn.

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