Survey design

Distance sampling is a survey method consisting of recording distances of detected animals from a survey transect or point, from which animal density and/or abundance can be estimated (Buckland et al., 2001; 2004). The typology of distance sampling implemented most commonly is line transect sampling, where a survey region is sampled by placing a series of evenly spaced parallel lines with a random start point (Thomas et al., 2010). A Marine Mammal Observer (MMO) aboard a survey vessel is transported along each line, with animals detected within a set distance (w) of the line recorded systematically, alongside their distance (m) from said line. In distance sampling, all animals on the line are assumed to be detected with certainty, although detection probability decreases with increasing distance from the line. In the instance of animals occurring in well‐defined clusters, detections refer to clusters rather than to individual animals. High-quality survey design, like that offered by OSC, enables animal/population density estimates to be extended to the entire survey region, thus allowing for estimation of animal abundance as well as influence of oceanographic drivers on presence.