4.1. Fish
In this study changes in schooling behaviour and vertical posi-
tion in trevally were observed at 147–151 dB re 1
l
Pa
2
.s. Specifi-
cally, at these noise levels the fish began to swim faster and form
more tightly cohesive groups towards the bottom of the cage. From
the data collected in trial 2, the pink snapper also moved to the
lower section of the cage. However, the behaviour of the pink snap-
per differed from the trevally in trial 1 in that loosely cohesive
groups was observed more often during exposure to noise. Also,
although alarm responses in the pink snapper were observed more
often during noise exposure there was a decrease in their fre-
quency when compared to the trevally.
These differences could be attributed to a number of factors.
Firstly, observations of pink snapper behaviour in trial 2 were
based on the second exposure to air gun noise in this trial as the
fish were out of view of the cameras for the first exposure. There-
fore, habituation to the noise from the first exposure could have re-
sulted in differences in behavioural responses. Secondly, species
naturally differ in their behavioural responses to noise exposure
and in hearing sensitivity (
Hawkins, 1981, 1986; Kastelein et al.,
2008; Popper et al., 2003
). Thirdly, the noise regime used in trial
2 differed from that in trial 1. Lastly, it should be noted that while
the trevally were wild caught, the pink snapper were sourced from