Seismic air guns, widely used in offshore resource exploration, are a major source of anthropogenic noise in marine environments. For some cetaceans, these impulsive sounds can disrupt acoustic communication critical for breeding and social interactions. Male humpback whales (Megaptera novaeangliae) produce long, highly structured songs as part of their reproductive display, often within areas overlapping seismic activity. This study investigated whether air gun noise alters the organisation and rate of humpback whale song. Four temporal parameters; inter-call interval, phrase duration, theme duration, song cycle duration, and one organisational variable (phrases per theme) were measured in the presence and absence of air gun pulses. Song cycle duration decreased by approximately 89 s during air gun exposure. Principal component analysis revealed two phrase categories, simple and complex, and showed that reductions in the repetition of complex phrases was the driver behind shorter theme and song cycle durations. Other parameters, such as inter-call interval and phrase duration, showed no consistent change, confirming that reduced complex phrase repetition was the main driver of song shortening. These findings provide evidence of a previously undocumented song-level response in singing humpback whales exposed to seismic air guns. They suggest that air gun noise may interfere with the production of complex song components, potentially distracting or confusing singers. Overall, this study highlights the need to consider sound type as well as amplitude when evaluating the effects of anthropogenic noise on marine mammals and demonstrates the vocal plasticity of humpback's vocal production in response to anthropogenic noise.

Audiograms are available for multiple species of odontocetes (toothed whales). However, there are no empirically measured audiograms for any mysticete (baleen whale) meaning their hearing sensitivity is inferred. Here, we present a masked hearing curve for the humpback whale (Megaptera novaeangliae) measured in natural ocean noise. We used a series of experiments to test responses to frequencies ranging from 0.25 to 16 kHz. Across multiple, independent trials, the mean of two lowest response received levels at each test frequency were used to calculate the minimum response level (MRL) for that frequency. Results show that the frequency range of humpback whales best hearing overlaps with anatomical predictions of their best hearing range, but their upper frequency limit of hearing is likely higher than expected. Response signal-to-noise ratios derived from the MRLs were close to frequency-dependent critical ratios (CR) observed in odontocetes, phocids, and otariids, suggesting the study measured close to masked thresholds in humpback whales.

Determining the frequency range of hearing and hearing sensitivity of baleen whales has long been a goal of marine mammal bioacousticians. Two recent investigations into baleen whale hearing, one on the common minke whale (Balaenoptera acutorostrata) and one on the humpback whale (Megaptera novaeangliae), have significantly advanced our understanding of baleen whale hearing. Thestudies used evoked potential audiometry, a direct measure of hearing, and modified behavioral observation audiometry, an indirect measure, to determine the frequency range of hearing and hearing sensitivity. Results from both studies suggest that these baleen whale species hear at higher frequencies than previously predicted based on vocalization frequencies and anatomical modeling. In the case of the minke whale, the frequency of best hearing sensitivity might reflect adaptations for predator detection or sound localization. In humpbacks, the received signal-to-noise ratios at which behavioral responses were observed were similar to critical ratios experimentally measured in multiple odontocete species. Additional research utilizing these techniques, and matched to species and populations where animals are available and show the behavioral and physiological traits suitable for their implementation (e.g., small size, predictable patterns of occurrence and behavior), will likely provide further information on baleen whale hearing.

Bottlenose dolphins produce individually distinctive signature whistles (SWs) to broadcast identity. Stability of the SW frequency contour is essential to preserve identity information; however, SWs could carry additional information which requires variability. We used acoustic recordings from provisioned free-swimming Indo-Pacific bottlenose dolphins at Moreton Island (Mulgumpin), Australia, collected in 2002 and 2017–2018, to assess the long-term (15-year) stability in SWs, and if variability of acoustic parameters increases with whistle complexity. Stability was assessed by analyzing basic contour parameters (minimum and maximum frequency, duration, etc.) and visually. We quantified SW variability using two developed variability metrics. Complexity was defined using four developed metrics, and its effect on variability was tested. Our results demonstrated that SW contours remain highly stable over time, but minimum frequency decreased by 8.8%. SWs also showed different degrees of variability between individuals. Variability appeared to be higher in males than in females, possibly indicating differences in SW use in different social contexts. Furthermore, SWs with a greater level of frequency modulation varied more than less modulated whistles. We propose that SWs possess sufficient variation in their frequency contour to contain additional information, possibly related to social and behavioral context, while still maintaining their identity function.

The Southern Ocean ecosystem is undergoing unprecedented environmental changes, which have led to shifts in the primary food source of baleen whales, Antarctic krill. Additionally, many humpback whale populations have rebounded from near extirpation due to historical whaling, increasing pressure on now vulnerable krill populations. Since humpback whales rely on energy reserves built up during their feeding season to sustain them during migration, changes in their food supply are likely to influence their migration strategies. In this study, the timing of the 'return to feeding grounds,' or southern migration, of the eastern Australian humpback whale population was tracked over a 21-year period. Both land-based and acoustic surveys were used to estimate the timing of the migratory peak in southern Queensland, i.e., the week with the highest number of whales sighted or recorded. Land-based surveys recorded all whales, including females with newborn calves, while acoustic surveys recorded singing adult males. Both datasets revealed that the peak of the southern migration has shifted earlier by approximately three weeks from 2003 to 2024. Although this study does not establish causation, it highlights a strong correlation between changes in migratory timing and sea ice coverage in the whales' Antarctic feeding grounds. The observed decline in sea ice area, combined with the large increase in the humpback whale population, are discussed as potential factors contributing to the shift in migratory timing.

Ocean noise produced by seismic exploration has been implicated in causing changes in baleen whale hearing, physiology, feeding, breeding, and migratory behaviours. Here, we observed changes in the mating tactics of humpback whales (Megaptera novaeangliae) during a one-hour exposure to nearby seismic air guns. Males employ a conditional mating strategy where they switch between singing and non-singing tactics. Singing is presumably an advertisement signal, while non-singing behaviours include seeking out and joining with females as well as forming competitive groups. During periods of active air guns, the number of male singing whales increased, and singers were more likely to be observed joining females. Conversely, non-singing males were less likely to engage in joining interactions suggesting that active air guns caused a switch in male breeding tactics. Though we cannot translate these effects into changes in breeding success, this indicates that seismic exploration has the potential to alter breeding behaviours in baleen whales. Male humpback whales respond to seismic air gun activity by increasing singing and breeding activity.

Many baleen whale species migrate between low-latitude breeding grounds and high-latitude feeding grounds, with increasing evidence that humpback whales Megaptera novaeangliae utilise supplemental feeding sites in temperate regions while migrating. The diet of whales while migrating is often unknown, and the impact that temperate feeding and/or fasting has on biochemical tracers used to investigate diet remains unclear. The aims of this study were to (1) determine whether prey consumption at supplemental feeding sites could be detected by carbon ( 13 C) and nitrogen ( 15 C) stable isotope analysis of skin; (2) obtain information on diet during migration; and (3) ascertain the impact of potential fasting on stable isotope values of baleen whales. Skin samples were taken from the eastern Australian humpback whale population on Antarctic feeding grounds and 2 sites on the southward migration route (a sub-tropical site and a temperate site) across 2 yr. At the sub-tropical site, 13 C and δ 15 N were consistent with the last place of foraging 5 mo earlier. One exception was the higher (0.5 ‰) δ 15 N value in 2011, suggesting that in some years, potentially when blubber reserves are insufficient, δ 15 N may be influenced by fasting. In both years, skin 13 C and δ 15 N values at the temperate site were higher than those from the Antarctic and sub-tropical sites, indicating that a feeding signal from temperate zones had likely been incorporated, with whales feeding on fish and krill. Importantly, supplemental feeding while migrating could affect the interpretation of whale diet on feeding grounds if sampled early in the season.

The health of migratory eastern Australian humpback whales (Megaptera novaeangliae) can reflect the condition of their remote polar foraging environments. This study used gene expression (LEP, LEPR, ADIQ, AhR, TNF-α, HSP-70), blubber hormone concentrations (cortisol, testosterone), and photogrammetric body condition to assess this sentinel species during a period of unprecedented changes to anthropogenic activity and natural processes. The results revealed higher cortisol concentrations in 2020 compared to 2021, suggesting a decline in physiological stress between years. Additionally, metabolic transcripts LEPR, and AhR, which is also linked to xenobiotic metabolism, were upregulated during the 2020 southbound migration. These differences suggest that one or more environmental stressors were reduced between 2020 and 2021, with upregulated AhR possibly indicating a Southern Ocean pollutant declined between the years. This research confirms a Southern Ocean-wide decrease in whale stress during the study period and informs efforts to identify key stressors on Antarctic marine ecosystems.

Currently, there are no direct data on mysticete hearing in noise. Available data comes from anatomical modelling, the assumption they can hear their own sounds, and studies on the effects of various sources of anthropogenic noise on their behavior. This study used a behavioral response study design to quantify humpback whale hearing in natural ocean noise. Tonal signals, ranging from 250 Hz to 16kHz, were used as the stimuli, and a change in humpback group behavior indicated the whales heard the signal. Individual whale and group behavior were quantified using a combination of land-based tracking data of groups and tag data deployed on individual whales to record fine-scale 3D movement underwater. The signal-to-noise ratio was estimated at the initial response position of the group or whale, assuming this was the level at which they first detected the tone in noise. Results confirm that humpback whales responded to signals in noise at detection levels comparable to other marine mammals and that their ability to hear signals in noise at higher frequencies is better than expected. This provides empirical data on hearing in a mysticete which can be used to better predict the acoustic impacts of anthropogenic noise on marine mammals.

Individually distinctive acoustic signals in animal vocal communication are taxonomically widespread, however, the investigation of these signal types in marine mammals has focused only on a few species. Humpback whale songs are a stereotyped, hierarchically structured vocal display performed by males, and hence thought to be sexually selected. Within a population, whales conform to a common version of the song despite the song constantly evolving. While humpback songs have been studied extensively at the population level, individual level variation has been rarely described, with inconclusive results. Here, we quantified inter- and intra-individual variability at different levels in the song hierarchy using songs from 25 singers across two song types from the eastern Australian population song of 2002 (12 singers), and the revolutionary song introduced in 2003 (13 singers). Inter-individual variability was found heterogeneously across all hierarchical levels of the song structure. In addition, distinct and individually specific patterns of song production were consistently recorded across song levels, with clear structural differences between the two song types. These results suggest that within the constraints of song conformity, males can produce individually distinctive patterns that could function as an advertisement to females to convey individual qualities.

Baleen whale sound perception is an important factor to consider when predicting and mitigating the impacts of anthropogenic ocean noise. Some sound types, for example predator calls, may elicit greater responses, meaning whale behavior is not only driven by proximity and received level, but other factors. Here, we compared the response of migrating eastern Australian humpback whales (Megaptera novaeangliae) to tones and airguns. We tested the hypothesis that groups would have a greater response magnitude to higher frequency tones given they sound like killer whale whistles, a known predator. An airgun shot, however, has a similar sound profile to a breaching whale. Whale groups were exposed to either a 20 cubic inch air gun or one of four tonal frequencies (250 Hz, 1 kHz, 4 kHz, and 16 kHz), and their behavior was compared before and during the sound exposure. Results show that the 16 kHz tone elicited the largest response as measured by alterations in group movement and dive behavior. Their behavioral changes to lower frequencies (250 Hz and 1 kHz) were similar in magnitude to their responses to airguns. Results suggest humpback whales may perceive certain sound types as threatening, eliciting more dramatic behavioral changes than conspecific-like sounds.

During the project “Behavioural Response of Australian Humpback whales to Seismic Surveys” three air gun configurations were used to quantify the response of southerly migrating humpback whales to a northerly travelling air gun. Off Peregian Beach, Queensland (26.5o S latitude) a 20 cubic inch (cui) single air gun, 440 cui and 3130 cui arrays were operated while off Dongara, Western Australia (29.5o S) the 440 cui array was operated. At a first glance, we assumed within the respective ∼200 km2 experimental areas sound propagation was reasonably uniform but this was not the case. At Peregian Beach, flat supposedly sandy areas had patchy outcrops of soft “coffee” rock which dramatically increased sound propagation loss while in the north a large arc of hard reef or shallow sand over reef again increased sound propagation loss and acted as an “amphitheatre.” Off Dongara different depths of sand or no sand over a limestone base created variable sound propagation. When comparing Dongara and Peregian Beach the shallow limestone off Dongara increased propagation loss compared to Peregian. This talk will explore some of the idiosyncrasies of air gun propagation and inhomogeneities which can be expected when planning sound exposure experiments.

There is concern that noise from “airguns” used during oil and gas exploration may cause behavioral changes in marine mammals. One important behavior of some mysticete whales is the production of songs which are likely used as reproductive displays. Humpback whales have conspicuous songs but there are few studies on the impact of noise on their singing behavior. Here, we test the hypothesis that airgun noise causes individual humpback whales to reduce the duration of their songs. In a series of experiments off the east coast of Australia, we exposed migrating humpback whales to airguns. We tracked and recorded singing males when we towed airguns through the study area as well as when there were no vessels or airguns present. We also noted interactions between singers and nearby conspecifics. Humpbacks usually stop singing when they join with others, and so joining is both a predictor of song duration and a biologically relevant outcome. Contrary to expectations, whales that were already singing prior to airgun exposure produced significantly longer songs than unexposed singers. However, the small number of whales that started singing during airgun exposure produced significantly shorter songs.

Recent photo-identification and genetic studies have identified at least five discrete breeding populations in Australia and Oceania: western Australia (D), eastern Australia (E (i)), New Caledonia (E (ii)), Tonga (E (iii)), French Polynesia and the Cook Islands (F). Also evident are low levels of intermingling among breeding populations consistent with the degree of genetic differentiation. Photo-identification has confirmed linkages between Area V feeding areas and eastern Australia breeding grounds and one genotype match has been reported between Area V feeding areas and Oceania breeding grounds. Recent abundance estimates show strong increases in the eastern Australian population, and some recovery in the New Caledonia and Tonga populations, but with little evidence of recovery at other known Oceania breeding grounds or New Zealand. Studies to date have provided no conclusive evidence of the migratory destination of humpback whales passing through New Zealand waters en route between Antarctic feeding areas and tropical breeding grounds. Photo-identification comparisons were undertaken between humpback whale fluke catalogues from eastern Australia (EA, 1315), Oceania east (OE, 513), Oceania west (OW, 166) and New Zealand (NZ, 13). Five matches were found between OE/OW, four matches between OW/EA and three matches between NZ/EA. The data are used to investigate and discuss the migratory destination and breeding ground migratory interchange of humpback whales travelling through New Zealand waters. The data confirm that humpback whales with site fidelity to eastern Australia migrate past New Zealand including through the Cook Strait and Foveaux Strait.

Marine Mammal ScienceVolume 39, Issue 2 p. 706-708 BOOK REVIEW Ethology and Behavioral Ecology of Mysticetes , Christopher W. Clark and Ellen C. Garland, Eds. Springer Nature. 2022. 384 pp. ISBN: 978–3–030-98448-9, US$169.99 (Hardcover); ISBN: 978–3–030-98448-9, US$129 (eBook) Michael Noad, Corresponding Author Michael Noad [email protected] Cetacean Ecology Group, The University of Queensland, Brisbane, Australia Correspondence Email: [email protected]Search for more papers by this author Michael Noad, Corresponding Author Michael Noad [email protected] Cetacean Ecology Group, The University of Queensland, Brisbane, Australia Correspondence Email: [email protected]Search for more papers by this author First published: 07 April 2023 https://doi.org/10.1111/mms.13016Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume39, Issue2April 2023Pages 706-708 RelatedInformation

The songs produced by male humpback whales are believed to be a reproductive display shared by all singers within the same population. Ocean noise can interfere with the transmission of acoustic signals such as humpback whale songs. However, humpback whales evolved in an environment characterised by variable levels of noise generated by natural sources. This study investigates whether singing males compensate for natural noise by changing the characteristics of their sounds. Songs were recorded off eastern Australia during periods of time when the soundscape was dominated by natural noise. Source level, peak frequency and duration were measured for 2,318 song units from 19 singers. Source levels were positively correlated with noise levels, while there was no correlation between the peak frequency or duration of the units and noise levels. Our study shows that male humpback whales increase the source level of their units in response to increasing natural noise, i.e. they have a Lombard response, but they do not modify their spectral or temporal characteristics. This suggests that the need to adhere to the shared repertoire prevents changes to distinctive features of song units, i.e. frequency and duration, however, vocal plasticity allows adjusting source levels to the environmental conditions.

Among animal species, the songs of male humpback whales (Megaptera novaeangliae) are a rare example of social learning between entire populations. Understanding fine-scale similarity in song patterns and structural features will better clarify how accurately songs are learned during inter-population transmission. Here, six distinct song types (2009-2015) transmitted from the east Australian to New Caledonian populations were quantitatively analysed using fine-scale song features. Results found that New Caledonian whales learned each song type with high accuracy regardless of the pattern's complexity. However, there were rare instances of themes (stereotyped patterns of sound units) only sung by a single population. These occurred more often in progressively changing 'evolutionary' songs compared to rapidly changing 'revolutionary' songs. Our results suggest that populations do not need to reduce complexity to accurately learn song patterns. Populations may also incorporate changes and embellishments into songs in the form of themes which are suggested to be learnt as distinct segments. Maintaining complex song patterns with such accuracy suggests significant acoustic contact, supporting the hypothesis that song learning may occur on shared feeding grounds or migration routes. This study improves the understanding of inter-population mechanisms for large-scale cultural transmission in animals.