Modeling variability in replicated surveys at aggregation sites

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



Surveys of aggregation sites can provide unbiased estimates of annual trends in population size if the proportion of the population counted at these sites does not vary systematically among years. However, counts at these sites tend to be highly variable and resulting trend estimates typically have poor precision. I developed an index based on a simple parametric model for counts of Pacific walruses (Odobenus rosmarus divergens) at haul-out sites in Bristol Bay, Alaska that accounted for the general temporal pattern of variability in the proportion of the population at the sites. Simulations suggested that an index based on mean annual counts was a more sensitive indicator of trend than the model-based index or the currently used index based on maximum annual counts. The model-based index may be more useful for other situations where timing of the aggregation peak is more variable.

Publication type Conference Paper
Publication Subtype Conference Paper
Title Modeling variability in replicated surveys at aggregation sites
ISBN 9789058090430
Year Published 1999
Language English
Publisher A.A. Balkema
Publisher location Rotterdam, Netherlands
Contributing office(s) Alaska Science Center
Description 11 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Marine mammal survey and assessment methods
First page 167
Last page 177
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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