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Marine Ecology Progress Series

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MEPS 632:221-234 (2019)  -  DOI:

Dynamic foraging by Risso’s dolphins revealed in four dimensions

Kelly J. Benoit-Bird1,*, Brandon L. Southall2,3, Mark A. Moline4

1Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039, USA
2Southall Environmental Associates, Inc., Aptos, CA 95003, USA
3University of California, Santa Cruz, Long Marine Laboratory, Santa Cruz, CA 95060, USA
4College of Earth, Ocean, and Environment, University of Delaware, Lewes, DE 19958, USA
*Corresponding author:

ABSTRACT: Quantifying details of an animal’s foraging strategy can provide insight into its energetic requirements, environmental constraints, and other pressures it must balance in behavioral decision-making. Data from ship-based echosounders provided 4888 observations of Risso’s dolphins Grampus griseus in the context of heterogeneous prey fields, while an autonomous underwater vehicle carrying similar instruments was used to describe 519 discrete prey patches containing dolphins. We integrated these data with prey net tows, dolphin surface observations, and results from a parallel tagging study that quantified detailed aspects of behavior of 3 individuals. These data provide complementary perspectives on the foraging strategies of Risso’s dolphins at a range of time scales from individual prey patch selection to diel cycles. Rather than being solely nocturnal teuthivores as previously suggested, we found that Risso’s dolphins dove to depths exceeding 500 m both day and night. Risso’s dolphins switched many times daily from being more generalist predators near the surface to specializing on larger squid at depth, commonly within the course of a single 5-10 min dive. Simple energy calculations suggest that shallow prey comprise relatively small contributions to individual energy gains, yet these prey played a strong role in determining the spatio-temporal habitat use of Risso’s dolphins. This underscores the importance of examining strategic foraging behavior in light of requirements to access both prey resources and oxygen. The novel integration of multiple complementary sensing methods employed simultaneously on Risso’s dolphins provide remarkable insights into the behavioral ecology of individuals and the population.

KEY WORDS: Foraging strategy · Pelagic · Odontocete · Grampus griseus · Acoustics

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Cite this article as: Benoit-Bird KJ, Southall BL, Moline MA (2019) Dynamic foraging by Risso’s dolphins revealed in four dimensions. Mar Ecol Prog Ser 632:221-234.

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