An aerial survey method to estimate sea otter abundance

By:  and 
Edited by: Gerald W. GarnerSteven C. AmstrupJeffrey L. LaakeBryan F.J. ManlyLyman L. McDonald, and Donna G. Robertson



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 Conference Paper
Publication Subtype Conference Paper
Title An aerial survey method to estimate sea otter abundance
ISBN 9789058090430
Year Published 1999
Language English
Publisher A.A. Balkema
Publisher location Rotterdam, Netherlands
Contributing office(s) Alaska Biological Science Center
Description 14 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Marine mammal survey and assessment methods
First page 13
Last page 26
Conference Title Symposium on surveys, status & trends of marine mammal populations
Conference Location Seattle, WA
Conference Date 25-27 February, 1998
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