Determining a correction factor for aerial surveys of harbor seals in California

• Published in: Marine Mammal Science
• Main Authors: Harvey, James T., Goley, Dawn
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2011
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Pacific; Phoca vitulina
• Online Access: http://dx.doi.org/10.1111/j.1748-7692.2010.00446.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1748-7692.2010.00446.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1748-7692.2010.00446.x

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.