The Behavioural Response of Australian Fur Seals to Motor Boat Noise

Australian fur seals breed on thirteen islands located in the Bass Strait, Australia. Land access to these islands is restricted, minimising human presence but boat access is still permissible with limitations on approach distances. Thirty-two controlled noise exposure experiments were conducted on breeding Australian fur seals to determine their behavioural response to controlled in-air motor boat noise on Kanowna Island (39°10′S, 146°18′E). Our results show there were significant differences in the seals' behaviour at low (64–70 dB) versus high (75–85 dB) sound levels, with seals orientating themselves towards or physically moving away from the louder boat noise at three different sound levels. Furthermore, seals responded more aggressively with one another and were more alert when they heard louder boat noise. Australian fur seals demonstrated plasticity in their vocal responses to boat noise with calls being significantly different between the various sound intensities and barks tending to get faster as the boat noise got louder. These results suggest that Australian fur seals on Kanowna Island show behavioural disturbance to high level boat noise. Consequently, it is recommended that an appropriate level of received boat sound emissions at breeding fur seal colonies be below 74 dB and that these findings be taken into account when evaluating appropriate approach distances and speed limits for boats

Perceptual grouping in two visually reliant species: Humans (Homo sapiens) and Australian sea lions (Neophoca cinerea)

Kurylo, van Nest, and Knepper (1997 Journal of Comparative Psychology 111 126 - 134) have recently shown that hooded rats are able to judge the global orientation of an array of elements if orientation is signalled by the perceptual-grouping principle of proximity, but not if it is signalled by element alignment. Using a procedure designed to overcome some potential problems with the experiment of Kurylo et al, we found the same distinction in the perceptual processing of Australian sea lions. The sea lions were able to judge the orientation of arrays containing strong proximity and similarity information, but performed at chance levels judging arrays in which element alignment signalled global orientation. Human subjects were able to judge all three pattern types quickly and accurately. This is strong evidence of a qualitative distinction in the way in which perceptual grouping operates in humans and the non-human species tested. Whether this distinction is a consequence of evolutionary or experiential factors is a question for future research, but the mere fact of a qualitative difference holds important implications for our understanding of perceptual grouping

Mean and SE values for the acoustic parameters of male Australian fur seal bark calls during the playback experiments.

<p>Mean and SE values for the acoustic parameters of male Australian fur seal bark calls during the playback experiments.</p

Ethogram of Australian fur seal behaviours on Kanowna Island during playback study.

<p>Ethogram of Australian fur seal behaviours on Kanowna Island during playback study.</p

Description of evaluation methods to analyse the response of Australian fur seals during the noise playback experiments.

<p>Description of evaluation methods to analyse the response of Australian fur seals during the noise playback experiments.</p

Fitted multinomial probabilities from the maximum likelihood of the proportional odds model from the ordinal logistic analysis.

<p>Where 0 = no response; 1 = eye movements towards the sound source; 2 = body movement towards the sound source; and 3 = move away from the sound source. The four shaded areas of the stacked bar chart represent the fitted probabilities of the four responses (0, 1, 2 & 3) for each treatment. 0 is represented in white, 1 in light grey and these represent minimal or no responses, 2 is represented by dark grey and 3 in Black and these represent the stronger responses of seals hearing the boat noise.</p

An example of acoustic features of boat noise used in controlled noise experiments on Kanowna Island.

<p>Top Panel is motor boat noise showing the amplitude of the boat noise and Lower Panel is the spectrogram of motor boat noise, spectrogram parameters: 256-point FFT, 256-point Hanning window with 50% overlap.</p