Open AccessA METHOD FOR PREDICTING HARBOR SEAL ( PHOCA VITULINA ) HAULOUT AND MONITORING LONG‐TERM POPULATION TRENDS WITHOUT TELEMETRY
Author(s) -
COWLES JONATHAN D.,
HENSON SHANDELLE M.,
HAYWARD JAMES L.,
CHACKO MATTHEW W.
Publication year - 2013
Publication title -
natural resource modeling
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.28
H-Index - 32
eISSN - 1939-7445
pISSN - 0890-8575
DOI - 10.1111/nrm.12015
Subject(s) - phoca , telemetry , harbor seal , population , term (time) , environmental science , fishery , biotelemetry , geography , ecology , computer science , biology , telecommunications , physics , demography , quantum mechanics , sociology
Monitoring population trends in harbor seals ( Phoca vitulina ) generally involves two steps: (i) a census obtained from aerial surveys of haul‐out sites, and (ii) an upward correction based on the proportion of seals hauled out as estimated from a sample of telemetry‐tagged seals. Here we present a mathematical method for obtaining site‐specific correction factors without telemetry. The method also determines site‐specific environmental factors associated with haulout and provides algebraic equations that predict diurnal haul‐out numbers and correction factors as functions of these variables. We applied the method at a haul‐out site on Protection Island, Washington, USA. The haul‐out model and correction factor model were functions of tide height, current velocity, and time of day, and the haul‐out model explained 46% of the observed variability in diurnal haul‐out dynamics. Although the particular models are site‐specific, the general model and methods are portable. A suite of such models for haul‐out sites of a regional stock would allow managers to monitor long‐term population trends without telemetry.