Using otoliths and scales to investigate the life history of American shad in the Columbia River

American Shad (Alosa sapidissima) were introduced to the Sacramento River, CA in 1871. Since then, they have expanded their range from southern California to southeast Alaska. Initially, the Columbia River population remained at low levels, but increased after dam construction improved spawning and rearing conditions. The number of adult shad passing Bonneville Dam peaked at over 5.2 million fish in 2004, but has since declined, with over 2.1 million fish passing the dam in 2008. Since American shad are non-native, well-established and prolific in the Columbia River, it is important to understand their potential impacts and interactions with threatened fish species, such as salmon. We are using otoliths and scales to add to our knowledge of Columbia River shad life history. We report on the size, age, and spawning history of adult shad captured at Bonneville Dam in 2008. Additionally, evidence is presented for the presence of an alternate juvenile life history type based on size and age at capture during downstream migration. Otolith microstructure and microchemistry analyses are used to further describe this life history type.