Snow and ice cover can camouflage seals, making it more difficult for scientists to estimate the animals' populations with accuracy.

The gray seal population in New England has bounced back, and new data points to how well seal numbers are doing.
Gray seal numbers had been decimated for more than a century when the Marine Mammal Protection Act was passed in 1972. The animals were hunted in New England, and as NPR has reported, Massachusetts even paid a bounty of $5 each.
Though it has been clear that the population has grown in number, it has been difficult to pinpoint just how much.
“Past surveys based on traditional methods of counting, using occupied aircraft to survey seals on beaches, islands and seasonal ice cover, counted about 15,000 seals off the southeastern Massachusetts coast,” David W. Johnson, a professor of marine conservation ecology at Duke’s Nicholas School of the Environment, said in a statement.
“Our technology-aided aerial survey, which used Google Earth imagery in conjunction with telemetry data from tagged animals, suggests the number is …
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