Endemic Guadalupe bass (Micropterus treculii) are supported by isotopically distinct resources in tributary versus mainstem river food webs

We used stable isotope analysis to investigate differences in Guadalupe bass (Micropterus treculii) resource use that might be associated with population-level variation in mainstem river versus tributary stream habitats. Guadalupe bass from mainstem sites had higher δ¹³C and δ¹⁵N values compared to those collected in tributaries, likely reflecting greater importance of algae as a basal resource and influences of urban wastewater in mainstem habitats. Documenting ecological variation across ecosystem types is important to inform fish conservation efforts, especially for species that occupy a range of stream sizes.