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MEPS 477:123-134 (2013)  -  DOI: https://doi.org/10.3354/meps10133

Contribution of prey to Humboldt squid Dosidicus gigas in the northern California Current, revealed by stable isotope analyses

Todd W. Miller1,*, Keith L. Bosley2, Junya Shibata1, Richard D. Brodeur3, Koji Omori1, Robert Emmett3,4

1Global Center of Excellence, Center for Marine Environmental Studies, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
2Fishery Resource Analysis and Monitoring Division, Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA, 2032 SE Marine Science Drive, Newport, Oregon 97365, USA
3Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA,
2030 SE Marine Science Drive, Newport, Oregon 97365, USA
4Present address: Northwest Fisheries Science Center, National Marine Fisheries Service, Point Adams Research Station,
520 Heceta Place, Hammond, Oregon 97121, USA

ABSTRACT: Diet studies have shown Humboldt squid Dosidicus gigas to be aggressive opportunistic predators, yet this approach has provided only a limited and potentially biased view of their trophic feeding behavior. As an alternative, we measured the δ13C and δ15N of D. gigas and their prey from the northern California Current ecosystem (NCC) and applied stable isotope Bayesian mixing models (Stable Isotope Analysis in R [SIAR]) to assess if D. gigas isotopically matched NCC or southern California Current (SCC) migratory end-members and to examine the proportional trophic contributions of prey groups from the NCC to their diet. For the trophic SIAR model, cluster analysis of prey taxa by their respective δ13C and δ15N values was first applied to consolidate prey into groups, which were then incorporated into the model as source groups to the diet mixture. Model results from examination of NCC and SCC migratory end-members indicated greatest contributions from the NCC system, indicating D. gigas was more integrated with the regional NCC isotopic signature. From the trophic SIAR model, the results indicated mixed but lower trophic-level feeding by D. gigas relative to previous diet-based studies, with greatest contributions from macrozooplankton, ichthyoplankton, and nekton such as juvenile rockfish, market squid, sand lance, and juvenile Pacific hake. Sensitivity analyses of the SIAR model based on varying isotopic fractionation factors of δ13C and δ15N showed that proportional contributions of prey to squid diets were resilient to change.


KEY WORDS: Humboldt squid · Dosidicus gigas · California Current · Stable isotopes · Bayesian mixing model · Trophic analysis · Prey


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Cite this article as: Miller TW, Bosley KL, Shibata J, Brodeur RD, Omori K, Emmett R (2013) Contribution of prey to Humboldt squid Dosidicus gigas in the northern California Current, revealed by stable isotope analyses. Mar Ecol Prog Ser 477:123-134. https://doi.org/10.3354/meps10133

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