Otolith Microchemistry of Coastal Cutthroat Trout from the Marys and Willamette Rivers.

Abstract We sampled the water chemistry and otolith chemistry and structure of juvenile Cutthroat Trout collected in the Marys River and adults collected in the Willamette River to evaluate the potential to identify life-history variation in this population. Differences in water chemistry between the Marys and the Willamette Rivers during the sampling period were reflected in otolith chemistry. We differentiated 2 life-history patterns: juveniles whose mothers appeared to be resident in the Marys River, and juveniles that likely had fluvial mothers from the Willamette River. Otolith elemental composition of both juveniles and adults showed maternal effects on core chemistry, movement, or changes in elemental incorporation related to changes in ontogeny, growth, or seasonal changes in temperature. Water and otolith edge 87Sr/86Sr were consistently lower in the Willamette River than in the Marys River. Mean otolith 87Sr/86Sr during early life provided evidence that some adults reared in tributaries and migrated into the Willamette River later in life, whereas core 87Sr/86Sr for some juveniles shows that they likely originated from outside of the Marys River or are offspring of mothers that migrated into the Marys River to spawn. Based on otolith annuli, growth rates during early life were generally higher for adults than juveniles; these differences could reflect inter-annual, habitat, or life-history differences. Otolith 87Sr/86Sr and structural analyses hold promise for elucidating origin and life-history patterns of Willamette River cutthroat populations. [ABSTRACT FROM AUTHOR]