Climate change in the southeastern Bering Sea: impacts on pollock stocks and implications for the oscillating control hypothesis

Abstract

Concern about impacts of climate change in the Bering Sea prompted several research programs to elucidate mechanistic links between climate and ecosystem responses. Following a detailed literature review, Hunt et al. (2011) (Deep-Sea Res. II, 49, 2002) developed a conceptual framework, the Oscillating Control Hypothesis (OCH), linking climaterelated changes in physical oceanographic conditions to stock recruitment using walleye pollock (Theragra chalcogramma) as a model. The OCH conceptual model treats zooplankton as a single box, with reduced zooplankton production during cold conditions, producing bottom-up control of apex predators and elevated zooplankton production during warm periods leading to top-down control by apex predators. A recent warming trend followed by rapid cooling on the Bering Sea shelf permitted testing of the OCH. During warm years (2003-06), euphausiid and Calanus marshallae populations declined, post-larval pollock diets shifted from a mixture of large zooplankton and small copepods to almost exclusively small copepods, and juvenile pollock dominated the diets of large predators. With cooling from 2006-09, populations of large zooplankton increased, post-larval pollock consumed greater proportions of C. marshallae and other large zooplankton, and juvenile pollock virtually disappeared from the diets of large pollock and salmon. These shifts in energy flow were accompanied by large declines in pollock stocks attributed to poor recruitment between 2001 and 2005. Observations presented here indicate the need for revision of the OCH to account for shifts in energy flow through differing food-web pathways due to warming and cooling on the southeastern Bering Sea shelf.

Effects of copepod size on fish growth: a model based on data for North Sea sandeel

“…Variance in total zooplankton abundance does not seem to tell the whole story, and some more detailed hypotheses therefore involve the occurrence of qualitative and phenological changes in the food source (Beaugrand et al 2003, Möllmann et al 2003, van der Lingen et al 2006. Climate-induced alterations of the local copepod communities have been reported in both temperate and Arctic regions (Planque & Taylor 1998, Möllmann et al 2003, Beaugrand 2004, Helaouët & Beaugrand 2009, Coyle et al 2011, Kjellerup et al 2012.…”

Community-level response of fish larvae to environmental variability in the southeastern Bering Sea

“…After retrieval of the bongo nets, all fish larvae were removed from the cod ends, and a volume displacement measurement of remaining zooplankton (including small gelatinous zooplankton; large jellyfish were removed so as not to bias the displacement volume) was taken as a coarse measure of zooplankton wet weight biomass and an index of overall production at each station , Coyle et al 2008, 2011. All samples were preserved at sea in 5% buffered formalin seawater solution.…”

Forecasting Pink Salmon Production in Southeast Alaska Using Ecosystem Indicators in Times of Climate Change

“…Companion studies in Icy Strait also indicated that food quantity can be more important than food quality for growth and survival of juvenile salmon (Weitkamp and Sturdevant 2008). As a result, monitoring the composition, abundance, and timing of zooplankton taxa with diff erent life-history strategies may permit the detection of climate-related changes in the seasonality and interannual abundance of prey fi elds (Park et al 2004;Coyle et al 2011;). In contrast, "top-down" predation events can also aff ect salmon year-class strength by piscivorous fi sh .…”