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Marine Ecology Progress Series

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MEPS 490:267-284 (2013)  -  DOI:

Associations between North Pacific right whales and their zooplanktonic prey in the southeastern Bering Sea

Mark F. Baumgartner1,*, Nadine S. J. Lysiak1, H. Carter Esch1, Alexandre N. Zerbini2, Catherine L. Berchok2, Phillip J. Clapham2

1Biology Department, Woods Hole Oceanographic Institution, 266 Woods Hole Road, MS #33, Woods Hole, Massachusetts 02543, USA
2National Marine Mammal Laboratory, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, Washington 98115, USA

ABSTRACT: Due to the seriously endangered status of North Pacific right whales Eubalaena japonica, an improved understanding of the environmental factors that influence the species’ distribution and occurrence is needed to better assess the effects of climate change and industrial activities on the population. Associations among right whales, zooplankton, and the physical environment were examined in the southeastern Bering Sea during the summers of 2008 and 2009. Sampling with nets, an optical plankton counter, and a video plankton recorder in proximity to whales as well as along cross-isobath surveys indicated that the copepod Calanus marshallae is the primary prey of right whales in this region. Acoustic detections of right whales from sonobuoys deployed during the cross-isobath surveys were strongly associated with C. marshallae abundance, and peak abundance estimates of C. marshallae in 2.5 m depth strata near a tagged right whale ranged as high as 106 copepods m-3. The smaller Pseudocalanus spp. was higher in abundance than C. marshallae in proximity to right whales, but significantly lower in biomass. High concentrations of C. marshallae occurred in both the surface and bottom layers of the highly stratified water column, but there was no evidence of diel vertical migration. Instead, occurrence of C. marshallae in the bottom layer was associated with elevated near-bottom light attenuance and chlorophyll fluorescence, suggesting C. marshallae may aggregate at depth while feeding on resuspended phytodetritus. Despite the occasional presence of strong horizontal gradients in hydrographic properties, no association was found between C. marshallae and either fronts or phytoplankton distribution.

KEY WORDS: Eubalaena japonica · Right whale · Calanus marshallae · Calanus glacialis · Bering Sea · Baleen whale · Resuspension · Phytodetritus

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Cite this article as: Baumgartner MF, Lysiak NSJ, Carter Esch H, Zerbini AN, Berchok CL, Clapham PJ (2013) Associations between North Pacific right whales and their zooplanktonic prey in the southeastern Bering Sea. Mar Ecol Prog Ser 490:267-284.

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