title: Listening in on the past: what can otolith δ18O values really tell us about the environmental history of fishes?
abstract: Oxygen isotope ratios from fish otoliths are used to discriminate marine stocks and reconstruct past climate, assuming that variations in otolith δ18O values closely reflect differences in temperature history of fish when accounting for salinity induced variability in water δ18O. To investigate this, we exploited the environmental and migratory data gathered from a decade using archival tags to study the behaviour of adult plaice (Pleuronectes platessa L.) in the North Sea. Based on the tag-derived monthly distributions of the fish and corresponding temperature and salinity estimates modelled across three consecutive years, we first predicted annual otolith δ18O values for three geographically discrete offshore sub-stocks, using three alternative plausible scenarios for otolith growth. Comparison of predicted vs. measured annual δ18O values demonstrated >96% correct prediction of sub-stock membership, irrespective of the otolith growth scenario. Pronounced inter-stock differences in δ18O values, notably in summer, provide a robust marker for reconstructing broad-scale plaice distribution in the North Sea. However, although largely congruent, measured and predicted annual δ18O values did not fully match [ corrected]. Small, but consistent, offsets were also observed between individual high-resolution otolith δ18O values measured during tag recording time and corresponding δ18O predictions using concomitant tag-recorded temperatures and location-specific salinity estimates. The nature of the shifts differed among sub-stocks, suggesting specific vital effects linked to variation in physiological response to temperature. Therefore, although otolith δ18O in free-ranging fish largely reflects environmental temperature and salinity, we counsel prudence when interpreting otolith δ18O data for stock discrimination or temperature reconstruction until the mechanisms underpinning otolith δ18O signature acquisition, and associated variation, are clarified.
authors.affiliation: UMR CNRS-UM2-UM1-IFREMER-IRD 5119 Ecologie des Systèmes Marins Côtiers, Montpellier 2 University, Montpellier, France; Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Lowestoft, United Kingdom.
authors.forename: Audrey M
authors.initials: AM
authors.lastname: Darnaude
authors.affiliation: Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Lowestoft, United Kingdom; Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, United Kingdom.
authors.forename: Anna
authors.initials: A
authors.lastname: Sturrock
authors.affiliation: Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, United Kingdom.
authors.forename: Clive N
authors.initials: CN
authors.lastname: Trueman
authors.affiliation: UMR CNRS-UM2-UM1-IFREMER-IRD 5119 Ecologie des Systèmes Marins Côtiers, Montpellier 2 University, Montpellier, France.
authors.forename: David
authors.initials: D
authors.lastname: Mouillot
authors.affiliation: Edinburgh Ion Microprobe Facility, School of GeoSciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.affiliation: Population Ecology Division, Bedford Institute of Oceanography, Dartmouth, Canada.
authors.forename: Steven E
authors.initials: SE
authors.lastname: Campana
authors.affiliation: Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Lowestoft, United Kingdom.
authors.forename: Ewan
authors.initials: E
authors.lastname: Hunter
mesh_terms: D000818:Animals; D004777:Environment; D005399:Fishes / Q000502:physiology*; D009659:North Sea; D010037:Otolithic Membrane / Q000502:physiology*