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Humpback whale diets respond to variance in ocean climate and ecosystem conditions in the California Current

Conceptual diagram displaying the proposed relationship
TitleHumpback whale diets respond to variance in ocean climate and ecosystem conditions in the California Current
Publication TypeJournal Article
Year of Publication2016
AuthorsFleming A.H, Clark C.T, Calambokidis J, Barlow J
JournalGlobal Change Biology
Date Published2016/03
Type of ArticleArticle
ISBN Number1354-1013
Accession NumberWOS:000370491400021
Keywordscetacean foraging; changing climate; climate change; ecosystem shifts; euphausiids; feeding grounds; fish; food-web; forage; megaptera-novaeangliae; north pacific; North Pacific Gyre Oscillation; Pacific decadal oscillation; population-structure; ptychoramphus-aleuticus; sardine sardinops-sagax; stable-isotope; trophic amplification; Upwelling

Large, migratory predators are often cited as sentinel species for ecosystem processes and climate-related changes, but their utility as indicators is dependent upon an understanding of their response to environmental variability. Documentation of the links between climate variability, ecosystem change and predator dynamics is absent for most top predators. Identifying species that may be useful indicators and elucidating these mechanistic links provides insight into current ecological dynamics and may inform predictions of future ecosystem responses to climatic change. We examine humpback whale response to environmental variability through stable isotope analysis of diet over a dynamic 20-year period (1993-2012) in the California Current System (CCS). Humpback whale diets captured two major shifts in oceanographic and ecological conditions in the CCS. Isotopic signatures reflect a diet dominated by krill during periods characterized by positive phases of the North Pacific Gyre Oscillation (NPGO), cool sea surface temperature (SST), strong upwelling and high krill biomass. In contrast, humpback whale diets are dominated by schooling fish when the NPGO is negative, SST is warmer, seasonal upwelling is delayed and anchovy and sardine populations display increased biomass and range expansion. These findings demonstrate that humpback whales trophically respond to ecosystem shifts, and as a result, their foraging behavior is a synoptic indicator of oceanographic and ecological conditions across the CCS. Multi-decadal examination of these sentinel species thus provides insight into biological consequences of interannual climate fluctuations, fundamental to advancing ecosystem predictions related to global climate change.

Short TitleGlob. Change Biol.

The present examination of higher trophic-level response to climate variability suggests that humpback whales are useful indicators of ecosystem dynamics in the CCS. Their foraging behavior is a synoptic result of dynamic physical and biological conditions in the CCS, reflecting changes across multiple trophic levels due to contemporary climate variability and ultimately informing potential responses across these trophic levels due to climate change. Though variations in oceanographic conditions are occurring across daily and monthly timescales, the present examination of annual and multi-year scales provides useful insight into the scales most relevant to top-predator foraging and population-level responses.

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