22 – The challenge of monitoring coastal marine mammals^293and trends of the dugong population to inform the Indigenous management of the
dugong fishery (Fig. 22.1). A manned, high-winged aircraft is currently the most
efficient platform from which to survey dugongs over such a large area (see Marsh
et al. 2011 for references), although this platform is likely to be superseded by
unmanned aerial vehicles in the near future (Hodgson et al. 2013). Many variables
may prevent an observer from detecting a dugong, including its diving behaviour,
weather conditions such as glare and cloud cover, sea state, water turbidity and
observer inexperience or fatigue (Marsh and Sinclair 1989; Pollock et al. 2006).
Marsh and Sinclair (1989) separated the probability of detecting dugongs present in
a survey area into two components: (1) the probability of an animal being near
enough to the surface to be seen by an observer (availability bias); and (2) the
Fig. 2 2 .1. The Torres Strait aerial survey region showing the bathymetry, survey blocks and transect lines
flown within each block. Figure reproduced from Hagihara et al. (2016).