Data from: Integrating passive acoustic and visual data to model spatial patterns of occurrence in coastal dolphins

Fine-scale information on the occurrence of coastal cetaceans is
required to support regulation of offshore energy developments and
marine spatial planning. In particular, the EU Habitats Directive
requires an understanding of the extent to which animals from Special
Areas of Conservation (SAC) use adjacent waters, where survey effort
is often sparse. Designing survey regimes that can be used to support
these assessments is especially challenging because visual sightings
are expected to be rare in peripheral parts of a population’s range.
Consequently, even intensive visual line-transect surveys can result
in few encounters. Static passive acoustic monitoring (PAM) provides
new opportunities to extend survey effort by using echolocation click
detections to quantify levels of occurrence of coastal dolphins, but
this does not provide information on species identity. In NE Scotland,
assessments of proposed offshore energy developments required
information on spatial patterns of occurrence of bottlenose dolphins
in waters in and next to the Moray Firth SAC. Here, we illustrate how
this can be achieved by integrating data from broad-scale PAM arrays
with presence-only data from visual surveys. Generalized estimating
equations were used with PAM data to model the occurrence of dolphins
in relation to depth, distance to coast, slope, and sediment, and to
predict the spatial variation in the cumulative occurrence of all
dolphin species across a 4 × 4 km grid of the study area.
Classification tree analysis was then applied to available visual
sightings data to estimate the likely species identity of dolphins
sighted in each grid cell in relation to local habitat. By multiplying
these probabilities, it was possible to provide advice on spatial
variation in the probability of encountering bottlenose dolphins from
this protected population at a regional scale, complementing data from
surveys that estimate average density or overall abundance within a
region.