Rebecca A. Dunlop

Songs of male humpback whales, Megaptera novaeangliae, are involved in intersexual interactions

Male humpback whales produce complex songs during the breeding season, yet the singing behaviour of males and whether songs function in male contests and/or through female choice are still poorly understood. We investigated song function by obtaining simultaneous observations of the positions and movements of singing and nonsinging whales in real time during their migration off the east coast of Australia. We collected movement data by acoustic tracking using a hydrophone array, land-based visual tracking and observations from a small boat. Of the 114 singers analysed, 66 (58%) associated with conspecifics. Singers were significantly more likely to join groups containing a mother–calf pair than other groups. Males started to sing after joining groups only if they consisted of a mother–calf pair not escorted by another male. Singers also associated longer and sang for a significantly greater proportion of time with mother–calf pairs than any other group type. Associating with mother–calf pairs has been shown to be a reproductively successful strategy for males. In contrast, whales that joined singers were usually lone males; these associations were brief and singers typically stopped singing in the presence of other males. This is the highest reported incidence in humpback whales of males singing when escorting females and supports an intersexual function of song in humpback whales. We suggest that males joining singers are prospecting for females rather than engaging in male social ordering and that singing may incur the cost of attracting competing males.

Your attention please: increasing ambient noise levels elicits a change in communication behaviour in humpback whales (Megaptera novaeangliae)

High background noise is an important obstacle in successful signal detection and perception of an intended acoustic signal. To overcome this problem, many animals modify their acoustic signal by increasing the repetition rate, duration, amplitude or frequency range of the signal. An alternative method to ensure successful signal reception, yet to be tested in animals, involves the use of two different types of signal, where one signal type may enhance the other in periods of high background noise. Humpback whale communication signals comprise two different types: vocal signals, and surface-generated signals such as ‘breaching’ or ‘pectoral slapping’. We found that humpback whales gradually switched from primarily vocal to primarily surface-generated communication in increasing wind speeds and background noise levels, though kept both signal types in their repertoire. Vocal signals have the advantage of having higher information content but may have the disadvantage of loosing this information in a noisy environment. Surface-generated sounds have energy distributed over a greater frequency range and may be less likely to become confused in periods of high wind-generated noise but have less information content when compared with vocal sounds. Therefore, surface-generated sounds may improve detection or enhance the perception of vocal signals in a noisy environment.

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.

Non-song social call bouts of migrating humpback whales

The use of stereotyped calls within structured bouts has been described for a number of species and may increase the information potential of call repertoires. Humpback whales produce a repertoire of social calls, although little is known about the complexity or function of these calls. In this study, digital acoustic tag recordings were used to investigate social call use within bouts, the use of bouts across different social contexts, and whether particular call type combinations were favored. Call order within bouts was investigated using call transition frequencies and information theory techniques. Call bouts were defined through analysis of inter-call intervals, as any calls within 3.9 s of each other. Bouts were produced significantly more when new whales joined a group compared to groups that did not change membership, and in groups containing multiple adults escorting a female and calf compared to adult only groups. Although social calls tended to be produced in bouts, there were few repeated bout types. However, the order in which most call types were produced within bouts was non-random and dependent on the preceding call type. These bouts appear to be at least partially governed by rules for how individual components are combined.

Evidence of a Lombard response in migrating humpback whales (Megaptera novaeangliae)

The Lombard reflex is an increase in the subjects vocal levels in response to increased noise levels. This functions to maintain an adequate signal-to-noise ratio at the position of the receiver when noise levels vary. While it has been demonstrated in a small number of mammals and birds including some whales, it has not yet been shown to occur in one of the most vocal species of baleen whale, the humpback whale (Megaptera novaeangliae). Humpback whales were simultaneously visually and acoustically tracked (using an array of calibrated hydrophone buoys) as they migrated southward. Source levels of social vocalizations were estimated from measured received levels and a site-specific empirical sound propagation model developed. In total, 226 social vocalizations from 16 passing groups of whales were selected for final analysis. Noise levels were predominantly wind-dependent (from sea surface motion) and ranged from 81 to 108 dB re 1 μPa in the 36 Hz-2.8 kHz band. Vocalization source levels increased by 0.9 dB for every 1 dB increase in wind-dependent background noise levels, with source levels (at 1 m) being maintained ∼60 dB above the noise level.

Behavioral-Response Studies: Problems With Statistical Power

The behavioral-response study (BRS) is an experimental design used by field biologists to determine the function and/or behavioral effects of conspecific, heterospecific, or anthropogenic stimuli. Although this has been used for many years in studies of acoustic stimuli and whales, many of these studies have been limited by lack of true replication, otherwise known as “pseudoreplication” (Hurlbert 1984; Kroodsma 1989; Searcy 1989).

The stress of four commercial farming practices, feeding, counting, grading and harvesting, in farmed rainbow trout,Oncorhynchus mykiss

Plasma cortisol concentrations in farmed rainbow trout (Oncorhynchus mykiss) were used to determine the stress caused by feeding, counting, grading and harvesting. The effect of carrying out these practices with the addition of an aerator was also determined. The cortisol concentration in trout plasma was assessed using enzyme immunoassay (EIA). Pre-feeding levels were found to be 3–4 ng/ml. Feeding, counting, grading and harvesting produced significant elevations in plasma cortisol. The presence of an aerator during these practices significantly reduced this cortisol response. The plasma cortisol response during winter grading was significantly less (p<0.0001) compared to summer grading. Grading was also found to be a more stressful practice than feeding or counting. The cortisol response to grading was dependent on fish size (p = 0.0027). Winter harvesting was more stressful than summer harvesting (p = 0.0134), suggesting that lower temperatures may prolong the loss of consciousness. This study suggests that stress incurred by the trout during fish farming practices can be significantly reduced by oxygenating the water.

Behavioral response of Australian humpback whales to seismic surveys.

The first of four major experiments in project behavioural response of australian humpback whales to seismic surveys (BRAHSS) was conducted on the east coast of Australia in September and October 2010. The project aims to understand how humpback whales respond to seismic surveys and to provide the information that will allow these surveys to be conducted efficiently with minimal impact on whales. It also aims to determine how the whales react to ramp up or soft start, and to assess how effective this is in mitigation. The 2010 experiment used a single air gun. Four air guns will be used in the next two experiments and a full seismic array in the final experiment in 2013. During the 2010 experiment, behavior and tracks of whales were recroded by four theodolite stations on elevated coastal positions and DTAGs used on some whales. Vocalizing whales were tracked with a wide base line hydrophone array. A further four acoustic recorders were used to measure propagation loss and to characterize the sound field throughout the area. A wide range of variables likely to affect whale response was measured. [Work sponsored by the JIP E&P Sound & Marine Life and Bureau of Ocean Energy Management, Regulation and Enforcement.]

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.