Fig. 4 Observations (dots) and model estimates (lines) of
porpoise behavioural responses to an approaching boat (averaged across
animals; data from phase 2 before the closest point of approach, i.e.
CPA). X-axis values were back-transformed from their logarithms. In a
and d, values on the y-axis were back-transformed from their cube root;
in b, c and d, bars show observed frequencies of a specific behaviour at
each distance range. Shaded areas show 95% confidence intervals. *
denotes significant models (p <0.025).
Porpoise behaviour before and during
exposure
The porpoises’ behaviour during the minute where the boat was closest
did not differ significantly from their behaviour before the experiment
started (their speed, absolute turning angles, and the probability of
diving or of breathing, were the same; p >0.05 for all
variables and both boat speeds; Fig. 5).