MEPS 317:297-310 (2006)  -  doi:10.3354/meps317297

Whale distribution in relation to prey abundance and oceanographic processes in shelf waters of the Western Antarctic Peninsula

Ari S. Friedlaender1,*, Pat N. Halpin1, Song S. Qian2, Gareth L. Lawson3, Peter H. Wiebe3, Deb Thiele4, Andrew J. Read1

1Duke University Marine Laboratory, 135 Pivers Island Road, Beaufort, North Carolina 28516, USA
2Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina 27708, USA
3Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
4Deakin University, School of Ecology and Environment, Warrnambool, Victoria 3280, Australia

ABSTRACT: The Western Antarctic Peninsula (WAP) is a biologically rich area supporting large standing stocks of krill and top predators (including whales, seals and seabirds). Physical forcing greatly affects productivity, recruitment, survival and distribution of krill in this area. In turn, such interactions are likely to affect the distribution of baleen whales. The Southern Ocean GLOBEC research program aims to explore the relationships and interactions between the environment, krill and predators around Marguerite Bay (WAP) in autumn 2001 and 2002. Bathymetric and environmental variables including acoustic backscattering as an indicator of prey abundance were used to model whale distribution patterns. We used an iterative approach employing (1) classification and regression tree (CART) models to identify oceanographic and ecological variables contributing to variability in humpback Megaptera novaeangliae and minke Balaenoptera acutorstrata whale distribution, and (2) generalized additive models (GAMs) to elucidate functional ecological relationships between these variables and whale distribution. The CART models indicated that the cetacean distribution was tightly coupled with zooplankton acoustic volume backscatter in the upper (25 to 100 m), and middle (100 to 300 m) portions of the water column. Whale distribution was also related to distance from the ice edge and bathymetric slope. The GAMs indicated a persistent, strong, positive relationship between increasing zooplankton volume and whale relative abundance. Furthermore, there was a lower limit for averaged acoustic volume backscatter of zooplankton below which the relationship between whales and prey was not significant. The GAMs also supported an annual relationship between whale distribution, distance from the ice edge and bathymetric slope, suggesting that these are important features for aggregating prey. Our results demonstrate that during the 2 yr study, whales were consistently and predictably associated with the distribution of zooplankton. Thus, humpback and minke whales may be able to locate physical features and oceanographic processes that enhance prey aggregation.

KEY WORDS: Whale distribution · Zooplankton · Ice edge · Antarctica · SO GLOBEC · CART · GAM

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