And Peter L. Boveng
NOAA Alaska Fisheries Science Center
National Marine Mammal Laboratory
Getting an accurate count of harbor seals is not an easy task. By nature, marine mammals are difficult to study because they are in the water most (or all) of the time and therefore hidden from view. In the case of harbor seals, aerial surveys are flown in August when the highest numbers of seals are seen on shore, lying in the sun and molting their hair.
To count the seals, researchers fly the entire coastline and take pictures of groups of seals lying on the beaches. The percentage of seals that are in the water and missed during the aerial surveys must also be estimated. This is usually done in a separate tagging study.
A harbor seal tagging study was recently completed in Cook Inlet. In the last three years, the National Marine Mammal Laboratory, with help from the Kachemak Bay Research Reserve, has deployed transmitters on 76 harbor seals in Kachemak Bay and Cook Inlet. These transmitters record whether the seal is in or out of the water; this information is then used to determine a correction factor for the aerial surveys. The data are still being processed, but the number of harbor seals counted during a survey multiplied by the correction factor is how the total population will be estimated. It will be very interesting to see how the 2006 harbor seal census compares with previous counts in 2001.
Oriana Badajos is a biological technician at the Kachemak Bay Research Reserve. Peter Boveng is the Polar Ecosystems Program leader at the National Marine Mammal Laboratory.
To learn more about the National Marine Mammal Laboratory, please visit http://nmml.afsc.noaa.gov/.
If you have questions about Kachemak Bay, contact reserve staff at 235-4799 or visit their website at www.kbayrr.org. Sponsored by the Kachemak Bay Research Reserve.
Photo provided by Ori Badajos
(Please include photo/caption below by Oriana Badajos)
Caption: A typical aerial survey photograph of harbor seals lying on a rocky island. (Photograph taken in Tuxedni Bay)
Did you know that it takes five years to census harbor seals (Phoca vitulina) in the state of Alaska? Our coastline is so large and intricate that the harbor seal’s range, from the Aleutian Islands to Southeastern Alaska, is divided up into five sections. Researchers from the National Marine Mammal Laboratory fly aerial surveys over one section each year. This year, the Gulf of Alaska section (including Kachemak Bay) was surveyed. The last time this area was surveyed was in 2001, and the harbor seal population was estimated to be 31,648. This may seem like a lot of seals, but the population has actually declined in some areas by as much as 85 percent since the 1970s.
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