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Determining a correction factor for aerial surveys of harbor seals in California
Author(s) -
Harvey James T.,
Goley Dawn
Publication year - 2011
Publication title -
marine mammal science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.723
H-Index - 78
eISSN - 1748-7692
pISSN - 0824-0469
DOI - 10.1111/j.1748-7692.2010.00446.x
Subject(s) - phoca , aerial survey , mark and recapture , telemetry , harbor seal , geography , census , population , fishery , ecology , biology , demography , cartography , aerospace engineering , sociology , engineering
Abstract Counts of pinnipeds provide a minimal estimate of population size because some unknown proportion of individuals is in the water during surveys. We determined a correction factor (CF) for Pacific harbor seals ( Phoca vitulina richardii ) by estimating the proportion ashore of 180 seals tagged with flipper‐mounted radio tags throughout California. The mean proportions of tagged individuals ashore during four complete surveys in 2004 were not different between central and northern California ( F = 1.85, P = 0.18) or between sexes ( F = 0.57, P = 0.45), but a lesser proportion of weaners was ashore than subadults or adults ( F = 7.97, P = 0.001), especially in northern California. The CF calculated for the statewide census of harbor seals was 1.65, using transmitters operating during the survey ( n = 114). Using a mark‐recapture estimator for tag survival ( phi ) and the four telemetry surveys the mean CF for central and northern California was 1.54 ± 0.38 (95% CI). A CF for southern California of 2.86 was based on a single survey. Using the mean CF of 1.54 and a statewide count in 2009 we estimated 30,196 (95% CI = 22,745–37,647) harbor seals in California.