DOI: 10.25338/b8ww5d
title: CNS isotope values in eye lenses for juvenile and adult Chinook Salmon

description: 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-characterized food webs. This experimental approach allowed us to
 directly measure diets and quantify tissue turn-over rates in eye lenses
 as well as the isotopic fractionation among fish tissues (fin and muscle
 tissue) in distinct habitat types using stable isotopes δ¹³C, ẟ¹⁵N, δ34S.
 Bulk eye lens stable isotope measurements were analyzed for juvenile
 salmon lenses and were found to be consistent with the isotopic values of
 rearing habitats. Slight additional isotopic fractionation was only found
 in δ¹³C. We then successfully applied the method to a larger,
 reproductively mature adult salmon captured in freshwater and inferred
 juvenile habitat use. SIA in eye lenses using three dietary isotopes
 (δ¹³C, ẟ¹⁵N, and δ34S), has significant potential for answering critical
 questions about migration, diet, foraging ecology, and life-history of
 migratory aquatic animals on Earth. Such information would have immediate
 application towards conservation management of diverse species and
 habitats at multiple scales.
description: Juvenile fish were collected from a previous field experiement
 outlined in Jeffres et al. (2020).  Laminae from both eyes of individual
 fish were combined for bulk analyses to meet minimum dry weight
 requirements for combined δ¹³C, δ¹⁵N, and δ³⁴S analysis (2mg) and
 submitted to the UC Davis Stable Isotope Facility for isotope analysis.
 Individual laminae from a single juvenile salmon from the floodplain was
 analyzed for δ¹³C, δ¹⁵N, and δ³⁴S to test the feasibility of
 reconstructing diets over smaller temporal and spatial scales of habitat
 use.    In 2014, the carcass of one stray adult Chinook
 Salmon with intact adipose fin was recovered near our Yolo Bypass
 floodplain study site. Individual laminae were separated and analyzed for
 isotopic variations through time and submitted to the same isotope
 facility listed above.  Last data set contatins the
 lens diameters measured in juvenile Chinook Salmon that were reared on the
 floodplain. Lenses were mounted in Crystalbond resin, sectioned, and
 measured using established methods for otolith sagittae (Barnett-Johnson
 et al. 2008).
description: This is the raw data without any changes.