Bengtson, John L. and Phillips, Alana V. and Mathews, Elizabeth A. and Simpkins, Michael A. (2007) Comparison of survey methods for estimating abundance of harbor seals (Phoca vitulina) in glacial fjords. Fishery Bulletin, 105(3), pp. 248-255.
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The importance of glacial ice habitats to harbor seals (Phoca vitulina) in Alaska has become increasingly apparent. However, enumerating harbor seals hauled out on ice in glacial fjords has been difficult. At Johns Hopkins Inlet in Glacier Bay, Alaska, we compared a shore-based counting method to a large-format aerial photography method to estimate seal abundance. During each aerial survey, shore-based observers simultaneously counted seals from an observation post. Both survey methods incurred errors in double-counting and missing seals, especially when ice movements caused seals to drift between survey zones. Advantages of shore-based counts included the ability to obtain multiple counts for relatively little cost, distinguish pups from adults, and to distinguish mobile seals from shadows or glacial debris of similar size. Aerial photography provided a permanent record of each survey, allowing both a reconciliation of counts in overlapping zones and the documentation of the spatial distribution of seals and ice within the fjord.
|Title:||Comparison of survey methods for estimating abundance of harbor seals (Phoca vitulina) in glacial fjords|
|Journal or Publication Title:||Fishery Bulletin|
|Page Range:||pp. 248-255|
|Issuing Agency:||United States National Marine Fisheries Service|
|Depositing User:||Patti M. Marraro|
|Date Deposited:||18 Jun 2012 11:35|
|Last Modified:||18 Jun 2012 11:35|
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