Validating a Non-Lethal Method of Aging Endangered Juvenile Lost River and Shortnose Suckers

Populations of imperiled Lost River Deltistes luxatus, and Shortnose Chasmistes brevirostris, suckers in Upper Klamath Lake, Oregon are experiencing long-term decreases in abundance due to limited recruitment of juvenile suckers into the adult populations. Researchers use estimated ages based on fin rays to study environmental factors affecting year-class formation, generate annual juvenile sucker survival indices, and study variations in early life history. Biased or imprecise age estimates can lead to erroneous conclusions and have implications for age-based survival estimates, indications of recruitment, and growth estimators. We examined fin rays collected from individual suckers captured on multiple occasions and determined that juvenile suckers deposit a translucent increment on fin rays annually. Size at age data for suckers first captured as young as age-0 corroborated our finding of annual increment formation and indicate the first increments are formed at age-1. We used edge and marginal increment analysis conducted on fin rays to determine the timing of annual increment formation. Our results indicate that increment formation occurs on fin rays of juvenile suckers from October through May, and peaks between February and April.