Table 1: Explanatory factors initially included in the linear model. Use of continuous and discrete (category) variables follows suggestions of [14], where category variables are categorised in as few as possible meaningful categories, and ordinal variables are assumed to be continuous. Logistic variables are categorised as discrete with levels.

FactorVariable typeNotes

DateContinuousFrom day 1 to day 158
BoatCategory ( )Differences in height of sighting platform; possible differences in acoustics of boat engines
Time of dayContinuousThat is, 4:30 pm = 16.5
Behaviour of cetaceanCategory ( )Surfacing, feeding, and other
Number of humpback whalesContinuous
Number of killer whaleContinuous
Number of white-beaked dolphinsContinuous
Sea stateContinuous
Percentage of cloud coverContinuous
Weather conditionsCategory ( )Sun, Cloud, and rain
Wind directionCategory ( )N, E, S, W, and no wind
Tidal conditionsCategory ( )Flood or ebb
Swell heightContinuous
VisibilityContinuous
Sea surface temperatureContinuous
ObserverCategory ( )Three different observers recorded results