Improving population estimates by quantifying diving and surfacing patterns: a dugong example

Hagihara, Rie, Jones, Rhondda E., Grech, Alana, Lanyon, Janet M., Sheppard, James K., and Marsh, Helene (2014) Improving population estimates by quantifying diving and surfacing patterns: a dugong example. Marine Mammal Science, 30 (1). pp. 348-366.

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Abstract

Diving animals are available for detection from above the water when environmental conditions are favorable and the animals are near the surface. The number of animals that are unavailable for detection needs to be estimated to obtain unbiased population estimates. The current availability correction factors used in aerial surveys for the dugong (Dugong dugon) allow for variation in environmental conditions but use the average time dugongs spend near the surface (i.e., constant availability corrections). To improve availability estimates, we examined location and dive data from nine dugongs fitted with satellite telemetry units and time-depth recorders (TDRs) in eastern Australia. The effects of water depth, tidal conditions, and habitat types on dugong surfacing time were examined using generalized linear mixed models (GLMMs). We found that availability for detection differed with water depth, and depth-specific availability estimates were often lower than the constant estimates. The habitat effect was less influential, and there was no tidal effect. The number of dugongs estimated using depth-specific availabilities were higher than those obtained using constant availabilities across water depth. Hence, information on water depth can refine availability estimates and subsequent abundance estimates from dugong aerial surveys. The methodology may be applicable to other aquatic wildlife.

Item ID: 30717
Item Type: Article (Research - C1)
ISSN: 1748-7692
Keywords: availability bias, aerial survey, abundance estimation, population, generalized linear mixed model (GLMM), diving, dugong, Sirenia, marine mammal
Funders: Australian Marine Mammal Centre, School of Earth and Environmental Sciences, James Cook University (JCU), School of Marine and Tropical Biology, James Cook University (JCU), Graduate Research School, James Cook University (JCU), Sea World Australia, Project Aware, Winifred V Scott Foundation, Anonymous donor
Projects and Grants: Improving the accuracy of dugong aerial surveys by better correcting for availability bias
Date Deposited: 02 Jan 2014 23:24
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 100%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960802 Coastal and Estuarine Flora, Fauna and Biodiversity @ 100%
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