Stable Isotope Analysis of Otoliths Provides Insight into the Ecological Niche, Occurrence, and Habitat Associations of American Eels

Stable isotope analysis of stocked American eel (Anguilla rostrata) otoliths is a useful tool for documenting the ecology and habitat use of the species by using fish of known age and growth history from a well-defined environment. Whole otolith dissolution and gas source mass spectrometry were used to measure δ¹⁸O and δ¹³C in otoliths of stocked eels (age 1-7 years) collected 2008-2013 from the St. Lawrence River and Jones Creek, a tributary and stocking location. Otolith stable isotopes of both δ¹⁸O and δ¹³C produce distinct “creek” and “river” signatures indicative of occurrence and habitat use by the eel. Specific habitat associations in relation to size and age are confirmed by using quantitative electrofishing and microhabitat substrate data. Otolith δ¹⁸O and δ¹³C show a transition signature associated with movement from a creek to river habitat at intermediate sizes (total length, 300-400 mm).Stocked eels that remain in a creek habitat appear to be slightly slower-growing than eels of the same age found in a river habitat. Otolith signatures confirm growth rate and size influence activity (home range) and habitat associations. Isotopes of δ¹⁸O and δ¹³C in stocked eel otoliths can help us better understand the ecological niche of eels.