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New Research Shows Shifts in Killer Whale Diets

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Got Teeth? Killer Whale Teeth Sought for Foraging Ecology Project

If you have teeth collected from a killer whale carcass, please consider donating them to Dan Monson and his colleagues for analysis. The Killer Whale Foraging Ecology project needs more teeth to test the hypothesis that killer whale diets changed considerably during the second half of the 20th century and that killer whales played a role in historical declines of marine-mammal populations in the northeast Pacific Ocean. Killer whale teeth, along with information about where and when they were collected, would be extremely helpful to the research group. In return, donors of teeth will receive information about the specimen, such as age and ecotype (resident versus transient), based on genetic analysis.

Please contact:
Dan Monson
USGS Alaska Science Center
4210 University Drive
Anchorage, AK 99508
(907) 786-7161

Biologist Daniel Monson of the U.S. Geological Survey (USGS) Alaska Science Center is coauthor of a recent report on using stable-isotope analysis of teeth to investigate killer whale diets. This approach could shed light on the hypothesized role of killer whales in historical declines of marine-mammal populations in the northeast Pacific Ocean.

Longitudinal section of a killer whale tooth.
Above: Longitudinal section of a killer whale tooth. Earliest years of growth are to the right, at the tip of the tooth. Oldest, most recent years of growth are to the left, along the hollow pulp cavity. Tooth has been etched in formic acid to highlight growth layers. Scale in millimeters. Digital scan by Mike Etnier; learn more at URL http://www.appliedosteology.com/
. [larger version]

Monson and his coauthors—Seth Newsome (senior author) and Marilyn Fogel of the Carnegie Institution of Washington, and Michael Etnier of Applied Osteology—found that dentin growth layers in killer whale teeth provide a record of individual diet with near-annual resolution. Analysis of stable-isotope ratios in the layers revealed such information as changes in individual diets over time and differences in diet between groups. For example, the teeth of most individuals studied showed a decrease in δ15N values throughout the first 3 years of life that the authors interpret as evidence of gradual weaning. The teeth of two groups of killer whales studied—"resident" whales that inhabit small and predictable areas during the summer months, and "transients" that are generally less predictable and known to migrate over large distances—yielded chemical evidence consistent with expectations that the residents eat primarily fish and the transients eat primarily marine mammals. The analyzed teeth were obtained from archived collections of teeth collected from dead whales in California, Washington, and Alaska during the period 1961-2003.

Analysis of tooth dentin growth layers provides information that cannot be obtained through traditional field observations of such free-ranging and elusive species as killer whales. This approach is especially useful for examining historical dietary shifts because many museum and some archeological collections contain teeth. Analysis of such teeth may help resolve a recent debate concerning the role of killer whales in historical declines of marine mammals in the northeast Pacific Ocean. Killer whale predation is widely accepted as the main cause of the relatively recent (late 1980s and early 1990s) sea otter declines in the central Aleutian Islands; some scientists have hypothesized that shifting killer whale prey preferences also drove earlier declines in the region's populations of harbor seals, northern fur seals, and Steller sea lions. (For example, see "Collapsing Populations of Marine Mammals—the North Pacific's Whaling Legacy?" in Sound Waves, October 2003.) The authors' ongoing analysis of teeth from modern and historically collected individuals, especially individuals from Alaskan waters, may allow them to construct a timeline of foraging information that could be the best way to evaluate the role of killer whales in historical marine mammal declines.

The complete reference for the new publication is:

Newsome, S.D., Etnier, M.A., Monson, D.H., and Fogel, M.L., 2009 Retrospective characterization of ontogenetic shifts in killer whale diets via d13C and d15N analysis of teeth: Marine Ecological Progress Series, v. 374, p. 229-242, doi:10.3354/meps07747 [URL http://dx.doi.org/10.3354/meps07747].

Related Sound Waves Stories
Collapsing Populations of Marine Mammals—the North Pacific's Whaling Legacy?
October 2003

Related Web Sites
Orca, or Killer Whale (Orcinus orca) Foraging Ecology

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Icebreaker Surveys in the Arctic Ocean

Modeling Climate Change and Ocean Acidification

Sediment Transport at Cape Hatteras

How Avian Influenza Spreads

Research Shorebird Recovery May Require Restrictions on Bait

Awards Research Achievements in Parasitology

Staff Woods Hole Science Center Hosts Delegation from India

Oceanographer Joins NOAA's Integrated Ocean Observing System Program

Publications Shifts in Killer Whale Diets

Polar Bear Habitat Distribution

April 2009 Publications List

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