title: Humpback whale diets respond to variance in ocean climate and ecosystem conditions in the California Current.
abstract: 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.
authors.affiliation: Center for Marine Biodiversity & Conservation, Scripps Institution of Oceanography, La Jolla, CA, 92037, USA.|NOAA, National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, CA, 92037, USA.
authors.forename: Alyson H
authors.initials: AH
authors.lastname: Fleming
authors.affiliation: School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, PO Box 757220, Fairbanks, AK, 99775, USA.
authors.forename: Casey T
authors.initials: CT
authors.lastname: Clark
authors.affiliation: Cascadia Research Collective, Olympia, WA, 98501, USA.
authors.forename: John
authors.initials: J
authors.lastname: Calambokidis
authors.affiliation: NOAA, National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, CA, 92037, USA.
authors.forename: Jay
authors.initials: J
authors.lastname: Barlow
mesh_terms: D000818:Animals; D002140:California; D057231:Climate Change; D004032:Diet; D017753:Ecosystem; D005260:Female; D020387:Food Chain; D050640:Humpback Whale / Q000502:physiology*; D008297:Male; D009792:Oceans and Seas; D010140:Pacific Ocean; D012621:Seasons; D013696:Temperature
keywords: North Pacific Gyre Oscillation; Pacific Decadal Oscillation; cetacean foraging; climate change; ecosystem shifts; euphausiids; forage fish; upwelling