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Marine Ecology Progress Series

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MEPS 378:199-209 (2009)  -  DOI:

Multibeam echosounder observations reveal interactions between Antarctic krill and air-breathing predators

Martin J. Cox1,*, David A. Demer2, Joseph D. Warren3, George R. Cutter2, Andrew S. Brierley1

1Pelagic Ecology Research Group, Gatty Marine Laboratory, University of St. Andrews, Fife KY16 8LB, UK
2Advanced Survey Technology Program, Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, California 92037, USA
3School of Marine and Atmospheric Sciences, Stony Brook University, 239 Montauk Highway, Southampton, New York 11968, USA

ABSTRACT: A multibeam echosounder (MBE) was deployed on an inflatable boat (length = 5.5 m) to observe swarms of Antarctic krill Euphausia superba in the nearshore environment off Livingston Island, South Shetland Islands, Antarctica. Visual observations of air-breathing predators, including penguins and fur seals, were made from the boat at the same time. MBEs extend the 2-dimensional acoustic observations that can be made with conventional vertical echosounders to 3 dimensions, enabling direct observation of the surface areas and volumes of entire krill swarms. Krill swarms exhibited a wide range of various size metrics (e.g. height, length and width) but only a narrow range of surface-area-to-volume ratios or ‘roughnesses’, suggesting that krill adopt a consistent group behavior to maintain swarm shape. The variation in R was investigated using generalized additive models (GAMs). GAMs indicated that the presence of air-breathing predators influenced swarm shape (R decreased as the range to predators decreased, and the swarms became more spherical), as did swarm nearest-neighbor distance (R decreased with increasing distance) and swarm position in the water column (R decreased in the upper 70% of the water column). Therefore, swarm shape appears to be influenced by a combination of behavioral responses to predator presence and environmental variables. MBEs have the potential to contribute much to studies of krill, and can provide data to improve our understanding of the behavior of krill in situ.

KEY WORDS: Antarctic krill · Euphausia superba · Predator–prey interactions · Multibeam echosounder · Swarm morphology · Livingston Island

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Cite this article as: Cox MJ, Demer DA, Warren JD, Cutter GR, Brierley AS (2009) Multibeam echosounder observations reveal interactions between Antarctic krill and air-breathing predators. Mar Ecol Prog Ser 378:199-209.

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