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bioacoustics articles: Marine Mammal Science

Subject: bioacoustics articles: Marine Mammal Science
From: Jason Gedamke <>
Date: Fri, 07 May 2004 07:45:29 -0700
 Dusky dolphin (Lagenorhynchus obscurus) foraging in two different
 habitats: Active acoustic detection of dolphins and their prey.
 Kelly J. Benoit-Bird , Bernd Wursig and Cynthia J. McFadden
 Active-acoustic surveys were used to determine the distribution of dusky
 dolphins and potential prey in two different New Zealand locations. During
 seven survey days off Kaikoura Canyon, dusky dolphins were found within
 the Deep-Scattering Layer (DSL) at 2000 when it rose to within 125 m of
 the surface. As the DSL rose to 30 m at 0100, the observed depth of
 dolphins decreased, presumably as the dolphins followed the vertical
 migration of their prey. Acoustically identified subgroups of coordinated
 animals ranged from one to five dolphins. Time, depth of layer, and layer
 variance contributed significantly to predicting foraging dusky dolphin
 subgroup size. In the much shallower and more enclosed Admiralty Bay,
 dolphins noted at the surface as foraging were always detected with the
 sonar, but were never observed in coordinated subgroups during the brief
 (two-day) study there. In Admiralty Bay dolphin abundance was correlated
 with mean volume scattering from potential prey in the water column; and
 when volume scattering, an index of prey density, was low, dolphins were
 rarely present. Ecological differences between the deep waters of Kaikoura
 Canyon and the shallow nearshore waters of Admiralty Bay may result in
 differences in how, when, and in what social groupings dusky dolphins

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