Length at Age of Mottled Sculpin in a Regulated High-Elevation River

We characterized length-at-age relationships of mottled sculpin (Cottus bairdii) in the Lower Blue River, a regulated high-elevation river in the southern Rocky Mountain region, CO, USA. Sculpin was collected in May, August and October in a dry year and a wet year, and sagittal otoliths were sectioned for age estimation. Age-1 fish grew rapidly followed by slowed annual growth and a relatively long life span, with the oldest individual inferred to be 9 years old at 119 mm in total length. These patterns might be due to the altered flow regime characterized by hypolimnetic dam water release, resulting in suboptimal summer water temperatures for growth, oligotrophic conditions and low abundance of prey resources. Our study reports length-at-age relationships of a small-bodied species in an anthropogenically altered river, and additional research is warranted to compare their life history characteristics over space and time.