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An aerial survey method to estimate sea otter abundance

Marine mammal survey and assessment methods

By:
and
Edited by:
G.W. Garner, Steven C. Amstrup, J.L. Laake, B. F. J. Manly, L.L. McDonald, and Donna G. Robertson

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Abstract

Sea otters (Enhydra lutris) occur in shallow coastal habitats and can be highly visible on the sea surface. They generally rest in groups and their detection depends on factors that include sea conditions, viewing platform, observer technique and skill, distance, habitat and group size. While visible on the surface, they are difficult to see while diving and may dive in response to an approaching survey platform. We developed and tested an aerial survey method that uses intensive searches within portions of strip transects to adjust for availability and sightability biases. Correction factors are estimated independently for each survey and observer. In tests of our method using shore-based observers, we estimated detection probabilities of 0.52-0.72 in standard strip-transects and 0.96 in intensive searches. We used the survey method in Prince William Sound, Alaska to estimate a sea otter population size of 9,092 (SE = 1422). The new method represents an improvement over various aspects of previous methods, but additional development and testing will be required prior to its broad application.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
An aerial survey method to estimate sea otter abundance
Series title:
Marine mammal survey and assessment methods
Year Published:
1999
Language:
English
Publisher:
A. A. Balkema
Publisher location:
Rotterdam, the Netherlands
Contributing office(s):
Alaska Biological Science Center
Description:
13-26
Larger Work Type:
Report
Larger Work Subtype:
Other Report
Larger Work Title:
Marine mammal survey and assessment methods
First page:
13
Last page:
26