title: Sequential isotopic signature along gladius highlights contrasted individual foraging strategies of jumbo squid (Dosidicus gigas).
abstract: BACKGROUND
  Cephalopods play a major role in marine ecosystems, but knowledge of their feeding ecology is limited. In particular, intra- and inter-individual variations in their use of resources has not been adequatly explored, although there is growing evidence that individual organisms can vary considerably in the way they use their habitats and resources.
  
  
  RESULTS
  Using δ(13)C and δ(15)N values of serially sampled gladius (an archival tissue), we examined high resolution variations in the trophic niche of five large (>60 cm mantle length) jumbo squids (Dosidicus gigas) that were collected off the coast of Peru. We report the first evidence of large inter-individual differences in jumbo squid foraging strategies with no systematic increase of trophic level with size. Overall, gladius δ(13)C values indicated one or several migrations through the squid's lifetime (∼8-9 months), during which δ(15)N values also fluctuated (range: 1 to 5‰). One individual showed an unexpected terminal 4.6‰ δ(15)N decrease (more than one trophic level), thus indicating a shift from higher- to lower-trophic level prey at that time. The data illustrate the high diversity of prey types and foraging histories of this species at the individual level.
  
  
  CONCLUSIONS
  The isotopic signature of gladii proved to be a powerful tool to depict high resolution and ontogenic variations in individual foraging strategies of squids, thus complementing traditional information offered by stomach content analysis and stable isotopes on metabolically active tissues. The observed differences in life history strategies highlight the high degree of plasticity of the jumbo squid and its high potential to adapt to environmental changes.
authors.affiliation: IRD, LEMAR UMR CNRS/UBO/IRD 6539, Plouzané, France. anne.lorrain@ird.fr
authors.forename: Anne
authors.initials: A
authors.lastname: Lorrain
authors.forename: Juan
authors.initials: J
authors.lastname: Argüelles
authors.forename: Ana
authors.initials: A
authors.lastname: Alegre
authors.forename: Arnaud
authors.initials: A
authors.lastname: Bertrand
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Munaron
authors.forename: Pierre
authors.initials: P
authors.lastname: Richard
authors.forename: Yves
authors.initials: Y
authors.lastname: Cherel
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis; D049832:Decapodiformes / Q000378:metabolism / Q000502:physiology*; D009587:Nitrogen Isotopes / Q000032:analysis
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes