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NORTHWESTERN NATURALIST 89:1723 SPRING 2008 TIDAL INFLUENCE ON THE HAUL-OUT BEHAVIOR OF HARBOR
 

Summary: 17
NORTHWESTERN NATURALIST 89:17­23 SPRING 2008
TIDAL INFLUENCE ON THE HAUL-OUT BEHAVIOR OF HARBOR
SEALS (PHOCA VITULINA) AT A SITE AVAILABLE AT
ALL TIDE LEVELS
JESSIE PATTERSON AND ALEJANDRO ACEVEDO-GUTIE´ RREZ
Department of Biology, Western Washington University,
Bellingham, Washington 98225-9160 USA
ABSTRACT--Harbor Seals (Phoca vitulina) are the most abundant and widespread seal species
in Washington State. Most seal haul-out sites are unavailable at high tide, hence abundance es-
timates are conducted at low tide when it is commonly accepted that most seals are hauled-out.
On sites unaffected by tides, however, it is less clear whether tide level has an effect on seal
abundance. We counted hauled-out Harbor Seals from sunrise to sunset on floating water-break-
ers at Semiahmoo Marina, Washington, to examine the effect of tides on haul-out behavior. Be-
cause haul-out behavior is affected by several factors, we conducted mixed-factor analyses that
included tide level, tidal current, time of season, and time of day as fixed factors, and several
meteorological variables as random factors. The number of hauled-out Harbor Seals was sig-
nificantly associated with tide level, time of season, and time of day. Results suggest that seal
counts in Semiahmoo Marina should be made late in the pupping season and early in the af-
ternoon at moderately positive tide levels to achieve the highest counts. They also indicate that

  

Source: Acevedo, Alejandro - Department of Biology, Western Washington University

 

Collections: Environmental Sciences and Ecology