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A Comprehensive Approach for Estimating Harbor Seal Abundance in Alaska
poster
posted on 2016-01-13, 01:05authored byJosh LondonJosh London, Peter Boveng, Jay VerHoef, John Jansen, Kymberly Yano, Luciana Santos
Estimating the statewide abundance of harbor seals (Phoca
vitulina) in Alaska has always been challenging. Harbor seals
range from southeastern Alaska through the Aleutian Island chain
into Bristol Bay. Past eorts have involved dividing the state into
ve regions and conducting aerial surveys from small aircraft in
one of those regions annually. An estimate is only possible once
every ve years, and trends were determined from surveys
conducted by the Alaska Department of Fish and Game (ADFG) at
a small subset of sites. We present a comprehensive, new
approach that overhauls the design and techniques for aerial
surveys of harbor seals in coastal regions and tidewater glacier
habitats.
The new approach adopted by the NOAA National Marine
Mammal Laboratory (NMML) and ADFG allows surveys to be
conducted annually across the entire range. This is accomplished
by dividing the coastline into distinct survey units and focusing
survey eort such that units with more seals are surveyed more
frequently. This was rst implemented for the statewide surveys in
August 2008. Seven planes were distributed throughout most of
the range and new technologies were used to improve navigation
and data collection eciency during the surveys. We estimate
approximately 70 percent or more of the seals hauled out during
our survey were photographed from the air.
This approach also incorporates a new model of haul-out
behavior based on the deployment of over one hundred satellite
tags. The model accounts for eects of time of day, day of year and
tidal state. Seals are more likely to haul-out near mid-day within
15 minutes of the low tide during the August molt period. Not
only is this critical for estimating the number of seals in the water
at the time of a survey, it also provides additional exibility in the
timing and implementation of the survey. In collaboration with
ADFG, we hope this new approach will result in annual estimates
of harbor seal abundance and trends in Alaska.