Research Document - 2009/065
An assessment of some of the factors affecting observer efficacy during cetacean surveys in Canada’s Pacific Region
By L.M. Nichol
Abstract
Sighting and effort data from five cetacean population assessment surveys made in the Pacific region were pooled and analysed to examine the effect of three environmental variables, Beaufort sea state, swell height, and lighting condition (cloudy or clear), on sightings per effort hour. Sightings per effort hour declined for all species and groupings with increasing sea state or swell height. The effect was most pronounced for small cetaceans (porpoise and dolphins). Lighting conditions appeared to also affect sightings per effort hour; however the number of hours of effort when skies were cloudy was almost three times greater than when it was clear. The type of visual cue that a species presents is also a factor that affects detectability of cetaceans. The results are discussed in the context of the effectiveness of mitigation procedures used during seismic surveys that rely on the observations of Marine Mammal Observers.
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