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Marine Ecology Progress Series

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MEPS 423:269-278 (2011)  -  DOI:

Life in the lead: extreme densities of narwhals Monodon monoceros in the offshore pack ice

Kristin L. Laidre1,2,*, Mads Peter Heide-Jørgensen2

1Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, Washington 98105-6698, USA
2Greenland Institute of Natural Resources, c/o Greenland Representation, Strandgade 91, 3, Postboks 2151,
1016 Copenhagen K, Denmark

ABSTRACT: There is a paucity of information on abundance, densities, and habitat selection of narwhals Monodon monoceros in the offshore pack ice of Baffin Bay, West Greenland, despite the critical importance of winter foraging regions and considerable sea ice declines in the past decades. We conducted a double-platform visual aerial survey over a narwhal wintering ground to obtain pack ice densities and develop the first fully corrected abundance estimate using point conditional mark–recapture distance sampling. Continuous video recording and digital images taken along the trackline allowed for in situ quantification of winter narwhal habitat and for the estimation of fine-scale narwhal habitat selection and habitat-specific sighting probabilities. Abundance at the surface was estimated at 3484 (coefficient of variation [CV] = 0.46) including whales missed by observers. The fully corrected abundance of narwhals was 18044 (CV = 0.46), or approximately one-quarter of the entire Baffin Bay population. The narwhal wintering ground surveyed (~9500 km2) had 2.4 to 3.2% open water based on estimates from satellite imagery (NASA Moderate Resolution Imaging Spectroradiometer) and 1565 digital photographic images collected on the trackline. Thus, the ~18000 narwhals had access to 233 km2 of open water, resulting in an average density of ~77 narwhals km–2 open water. Narwhal sighting probability near habitats with <10% or 10 to 50% open water was significantly higher than sighting probability in habitats with >50% open water, suggesting narwhals select optimal foraging areas in dense pack ice regardless of open water availability. This study provides the first quantitative ecological data on densities and habitat selection of narwhals in pack ice foraging regions that are rapidly being altered with climate change.

KEY WORDS: Abundance · Density · Greenland · Narwhal · Pack ice · Site fidelity

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Cite this article as: Laidre KL, Heide-Jørgensen MP (2011) Life in the lead: extreme densities of narwhals Monodon monoceros in the offshore pack ice. Mar Ecol Prog Ser 423:269-278.

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