Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis

ICES Journal of Marine Science; doi:10.1093/icesjms/fsr036 Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis George L. Hunt Jr 1 *, Kenneth O. Coyle 3 , Lisa B. Eisner 4 , Edward V. Farley 4 , Ron A. Heintz 4 , Franz Mueter 5 , Jeffrey M. Napp 2 , James E. Overland 6 , Patrick H. Ressler 2 , Sigrid Salo 6 , and Phyllis J. Stabeno 6 School of Aquatic and Fishery Sciences, University of Washington, PO Box 355020, Seattle, WA 98195, USA NOAA-National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115, USA Institute of Marine Science, University of Alaska, Fairbanks, AK 99775-7220, USA NOAA-National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratories, 17109 Pt. Lena Loop Rd., Juneau, AK 99801, USA Juneau Center, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 11120 Glacier Highway, Juneau, AK 99801, USA NOAA/OAR Pacific Marine Environmental Laboratory, 7600 Sand Point Way, NE, Seattle, WA 98115 –6249, USA *Corresponding Author: tel: +1 206 441 6109; fax: +1 260 685 7471; e-mail: geohunt2@uw.edu Hunt, G. L., Coyle, K. O., Eisner, L. B., Farley, E. V., Heintz, R. A., Mueter, F., Napp, J. M., Overland, J. E., Ressler, P. H., Salo, S., and Stabeno, P. J. Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis. – ICES Journal of Marine Science, doi:10.1093/icesjms/fsr036 Received 29 June 2010; accepted 17 February 2011. Walleye pollock (Theragra chalcogramma) is an important component of the eastern Bering Sea ecosystem and subject to major fisheries. The Oscillating Control Hypothesis (OCH) predicted that recruitment of pollock year classes should be greatest in years with early ice retreat and late blooms in warm water, because more energy would flow into the pelagic (vs. benthic) community. The OCH further predicted that, with pollock population growth, there should be a shift from bottom-up to top-down regu- lation. New data support the predictions that in those years with early ice retreat, more primary production accrues to the pelagic compartment and that large numbers of age-0 pollock survive to summer. However, in these years, production of large crustacean zooplankton is reduced, depriving age-0 pollock of lipid-rich prey in summer and autumn. Consequently, age-0 pollock energy reserves (depot lipids) are low and predation on them is increased as fish switch to age-0 pollock from zooplankton. The result is weak recruitment of age-1 recruits the following year. A revised OCH indicates bottom-up constraints on pollock recruitment in very warm periods. Prolonged warm periods with decreased ice cover will likely cause diminished pollock recruitment and catches relative to recent values. Keywords: Bering Sea, climate change, crustacean zooplankton, Oscillating Control Hypothesis, sea ice cover, Theragra chalcogramma, walleye pollock, year-class strength. Introduction The Oscillating Control Hypothesis (OCH) was developed as a conceptual model of how walleye pollock (Theragra chalco- gramma) recruitment in the southeastern Bering Sea might be affected by climate variability (Hunt et al., 2002a, 2008). The OCH was based on several assumptions about the relation- ships between temperature, zooplankton, and the growth and survival of young pollock. It was an extension of the ideas of Walsh and McRoy (1986) working in the Bering Sea and of Bailey (2000), who had determined that the control of walleye pollock recruitment in the Gulf of Alaska had shifted from bottom-up control of early larval survival to top-down control of juvenile stages. The OCH extended Bailey’s work by attempting to develop explicit mechanistic hypotheses that would link pollock recruitment to the effects of climate in the southeastern Bering Sea. This paper reviews the assumptions and predictions of the OCH (Hunt et al., 2002a) and updates the OCH to account for new information available since 2002. The result is a new version of the OCH, which still predicts variation in the dominant mechanism for control of pollock recruitment and now hypothesizes that the dominant mechanism affecting pollock recruitment in stanzas of very warm years will be bottom-up impacts on the survival of age-0 pollock in their first autumn and winter. The eastern Bering Sea supports major fisheries, the largest of which is for walleye pollock, a gadid that is or has been the subject of fisheries throughout the northern Pacific Ocean from Puget Sound, WA, to the east coast of Japan and the Sea of Okhotsk (Hunt and Drinkwater, 2005). In the eastern Bering Sea, pollock biomass expanded rapidly in the 10 years after the 1976/ 1977 “regime shift” (Hare and Mantua, 2000), buoyed by the extra- ordinarily strong 1978 year class (Ianelli et al., 2010). Because International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oup.com

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