Eric Kniest

Multivariate analysis of behavioural response experiments in humpback whales (Megaptera novaeangliae)

SUMMARY The behavioural response study (BRS) is an experimental design used by field biologists to determine the function and/or behavioural effects of conspecific, heterospecific or anthropogenic stimuli. When carrying out these studies in marine mammals it is difficult to make basic observations and achieve sufficient samples sizes because of the high cost and logistical difficulties. Rarely are other factors such as social context or the physical environment considered in the analysis because of these difficulties. This paper presents results of a BRS carried out in humpback whales to test the response of groups to one recording of conspecific social sounds and an artificially generated tone stimulus. Experiments were carried out in September/October 2004 and 2008 during the humpback whale southward migration along the east coast of Australia. In total, 13 ‘tone’ experiments, 15 ‘social sound’ experiments (using one recording of social sounds) and three silent controls were carried out over two field seasons. The results (using a mixed model statistical analysis) suggested that humpback whales responded differently to the two stimuli, measured by changes in course travelled and dive behaviour. Although the response to ‘tones’ was consistent, in that groups moved offshore and surfaced more often (suggesting an aversion to the stimulus), the response to ‘social sounds’ was highly variable and dependent upon the composition of the social group. The change in course and dive behaviour in response to ‘tones’ was found to be related to proximity to the source, the received signal level and signal-to-noise ratio (SNR). This study demonstrates that the behavioural responses of marine mammals to acoustic stimuli are complex. In order to tease out such multifaceted interactions, the number of replicates and factors measured must be sufficient for multivariate analysis.

The Behavioural Response of Humpback Whales (Megaptera novaeangliae) to a 20 Cubic Inch Air Gun

Seismic surveys are widely used for exploration for oil and gas deposits below the sea floor. Despite concern they may have an impact on whale behaviour, our knowledge of marine mammal responses is limited. In the first of a series of experiments (the last one involving a full seismic array), this study tested the response of migrating humpback whale (Megaptera novaeangliae) groups to a 20 cubic inch air gun. Experiments were carried out during the southward migration of humpback whales along the east coast of Australia. Groups of whales were focally followed from land stations and/or small boats with observations before, during, and after exposure to a vessel towing the air gun. The source vessel moved either eastwards across the, migratory flow or northwards into the migratory flow In total, there were 18 control trials (where the source vessel ran the compressor and towed the air gun without it firing; n = 35 whale groups) and 16 active trials (where the air gun was firing every 11 s; a = 32 whale groups). The air gun source level was 199 dB re 1 mu Pa(2.)s (Sound Exposure Level [SEC]) at 1 m, and SELs received by the whales varied from 105 to 156 dB re 1 mu Pa(2.)s (modal value 128 dB re mu Pa(2.)s) for SELs at least 10 dB above the background noise (measured as dB re 1 mu Pa). Other baseline groups were focal followed when there was no source vessel in the area (n = 25). Results suggested that humpback whale, groups responded by decreasing both dive time and speed of southwards movement though the response magnitude was not found to be related to the proximity of the source vessel, the received level of the air gun, the tow path direction, or the exposure time, within the during phase. There was no evidence of orientation of the groups towards, or away from, the source vessel in the during phase. Interestingly, this behavioural response was found in the control trials as well as the active trials suggesting a response to the source vessel.

Determining the behavioural dose-response relationship of marine mammals to air gun noise and source proximity

ABSTRACT The effect of various anthropogenic sources of noise (e.g. sonar, seismic surveys) on the behaviour of marine mammals is sometimes quantified as a dose–response relationship, where the probability of an animal behaviourally ‘responding’ (e.g. avoiding the source) increases with ‘dose’ (or received level of noise). To do this, however, requires a definition of a ‘significant’ response (avoidance), which can be difficult to quantify. There is also the potential that the animal ‘avoids’ not only the source of noise but also the vessel operating the source, complicating the relationship. The proximity of the source is an important variable to consider in the response, yet difficult to account for given that received level and proximity are highly correlated. This study used the behavioural response of humpback whales to noise from two different air gun arrays (20 and 140 cubic inch air gun array) to determine whether a dose–response relationship existed. To do this, a measure of avoidance of the source was developed, and the magnitude (rather than probability) of this response was tested against dose. The proximity to the source, and the vessel itself, was included within the one-analysis model. Humpback whales were more likely to avoid the air gun arrays (but not the controls) within 3 km of the source at levels over 140 re. 1 µPa2 s−1, meaning that both the proximity and the received level were important factors and the relationship between dose (received level) and response is not a simple one. Highlighted Article: An analytical framework relating the behavioural response of whales to received level and proximity of a noise source, with dose–response results of humpback whales to air guns.

The behavioural response of migrating humpback whales to a full seismic airgun array

Despite concerns on the effects of noise from seismic survey airguns on marine organisms, there remains uncertainty as to the biological significance of any response. This study quantifies and interprets the response of migrating humpback whales (Megaptera novaeangliae) to a 3130 in3 (51.3l) commercial airgun array. We compare the behavioural responses to active trials (array operational; n = 34 whale groups), with responses to control trials (source vessel towing the array while silent; n = 33) and baseline studies of normal behaviour in the absence of the vessel (n = 85). No abnormal behaviours were recorded during the trials. However, in response to the active seismic array and the controls, the whales displayed changes in behaviour. Changes in respiration rate were of a similar magnitude to changes in baseline groups being joined by other animals suggesting any change group energetics was within their behavioural repertoire. However, the reduced progression southwards in response to the active treatments, for some cohorts, was below typical migratory speeds. This response was more likely to occur within 4 km from the array at received levels over 135 dB re 1 µPa2.s.

Addressing challenges in studies of behavioral responses of whales to noise

Studying the behavioral response of whales to noise presents numerous challenges. In addition to the characteristics of the noise exposure, many factors may affect the response and these must be measured and accounted for in the analysis. An adequate sample size that includes matching controls is crucial if meaningful results are to be obtained. Field work is thus complicated, logistically difficult, and expensive. This paper discusses some of the challenges and how they are being met in a large-scale multiplatform project in which humpback whales are exposed to the noise of seismic air guns.

A behavioural dose-response model for migrating humpback whales and seismic air gun noise

The behavioural responses of migrating humpback whales to an air gun, a small clustered seismic array and a commercial array were used to develop a dose-response model, accounting for the presence of the vessel, array towpath relative to the migration and social and environmental parameters. Whale groups were more likely to show an avoidance response (increasing their distance from the source) when the received sound exposure level was over 130 dB re 1 μPa2·s and they were within 4 km of the source. The 50% probability of response occurred where received levels were 150-155 dB re 1 μPa2·s and they were within 2.5 km of the source. A small number of whales moving rapidly close to the source vessel did not exhibit an avoidance response at the highest received levels (160-170 dB re 1 μPa2·s) meaning it was not possible to estimate the maximum response threshold.

The Humpback Whale Acoustic Research Collaboration studies on the use of sound by humpback whales

Humpback whales produce two different types of vocalizations with apparent difference functions: songs and social sounds. There is also the potential to use the sounds of their environment, such as surf noise during migration along coasts, though this has not been demonstrated. The Humpback Whale Acoustic Research Collaboration (HARC) is a series of well‐controlled, multiplatform experiments designed to improve our understanding of how humpback whales use sound, both vocalizations and sounds of their environment. There have been two major experiments with humpback whales migrating along the east coast of Australia. Whales passing within 10 km were tracked acoustically and visually during daylight hours in conjunction with behavioral observations, and DTAGs were used on some whales to record their 3D movements and the sound field to which they were exposed. There was also playback of social sounds and full characterization of the acoustics of the environment, including the ambient noise exposure. Preliminary results of interactions between singing and nonsinging whales, the use of song as a spacing mechanism, responses to playback, and context of social sounds will be discussed. [Research supported by ONR and DSTO.]