CNS isotope values in eye lenses for juvenile and adult Chinook Salmon

Tracking habitat use and dietary shifts in migratory species is vital to conservation and management. Yet conventional animal tracking often precludes tracking small juveniles at critical life-stages where recruitment bottlenecks often manifest. Stable isotope analysis (SIA) in consecutive laminae in eye lenses, a protein-rich depositional tissue, has emerged as a promising tool in fishes to develop long-term interpretive records of dietary histories using a single archival tissue. Currently, studies using fisheye lenses to study SIA in diets have primarily been conducted in marine environments using δ¹³C and δ¹⁵N to identify resource partitioning, ontogenetic shifts, and lifelong trophic histories. To date, no studies have examined freshwater taxa nor used δ³⁴S isotopes. We placed juvenile Chinook Salmon (Oncorhynchus tshawytscha) in experimental enclosures in three different freshwater habitats (hatchery, river, and seasonal floodplain), each with isotopically distinct and well-...