Date of Award

2011

Document Type

Thesis

Degree Name

Master of Science

School

College of Arts and Sciences

Program

Biology MS

First Advisor

James L. Hayward

Second Advisor

Shandelle M. Henson

Abstract

Harbor seals haul out in response to various environmental factors such as tide, current, time of day, wind, and surf. Mathematical modeling techniques can be used to determine which of these variables are important and to predict the number of seals that will haul-out in a given set of environmental circumstances. Haul-out counts were recorded every hour for 16 hrs per day over two 14-d tidal cycles at a site in Washington State. Deterministic environmental variables (tide height, current velocity, solar elevation, and time of day) were used to create 37 alternative models, which were then compared to the haul-out data using information theoretic model selection techniques. The best model contained the environmental variables tide, current, and time of day and explained >45% of the observed variability. It revealed, in the morning, that maximal seal haul-out occurs several hours before low tide, and seals begin returning to the water at low tide. Higher haul-out numbers are observed in the afternoon and evening, and fewer seals reenter the water at low tides that occur in the afternoon. The results of this study are site-specific, but the methods used are portable and useful for researchers and wildlife managers interested in monitoring haul-out or population trends over time.

Subject Area

Seals (Animals)--Research--Mathematical models.

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