Pygmy Blue Whales Research Articles

Assessing exposure risk to microplastics by Indian Ocean pygmy blue whales

Microplastics (MPs) have attracted widespread attention due to their ubiquitous occurrence and harmful effects, however, limited data are available regarding the quantity and composition of MPs ingested by blue whales. In this study, MPs were detected in fecal samples obtained from pygmy blue whales (Balaenoptera musculus brevicauda) (n = 18, mean 0.82 items/g d.w) and seawater samples (n = 5, mean 143 ± 60.0 items/m3) from the northern Indian Ocean. Six polymer types were identified using micro-Fourier-transform infrared spectroscopy (μ-FTIR), nearly half of which were polyethylene terephthalate (PET). The variety of shapes, colors, and polymer types of MPs in blue whale fecal samples indicated the diversity of ingested MPs. For pygmy blue whales, MP ingestion exposure was estimated as high as 1.74 (± 0.83) × 106 items/day according to typical filter-feeding rates estimated for this sub-species. We suggested that the ingested MPs were mainly from trophic transfer rather than environmental exposure, and this MP ingestion may pose a minimal risk of caloric deficit. This study provides essential baseline information on the MP loads in pygmy blue whales in the Indian Ocean and considers the potential adverse impacts of long-term exposure to MPs.

Diverse baleen whale acoustic occurrence around two sub-Antarctic islands: A tale of residents and visitors

Knowledge on the occurrence and behaviour of baleen whales around sub-Antarctic regions is limited, and usually based on short, seasonal sighting research from shore or research vessels and whaling records, neither of which provide accurate and comprehensive year-round perspectives of these animals’ ecology. We investigated the seasonal acoustic occurrence and diel vocalizing pattern of baleen whales around the sub-Antarctic Prince Edward Islands (PEIs) using passive acoustic monitoring data from mid-2021 to mid-2023, detecting six distinct baleen whale songs from Antarctic blue whales, Madagascan pygmy blue whales, fin whales, Antarctic minke whales, humpback whales, and sei whales. Antarctic blue and fin whales were detected year-round whereas the other species’ songs were detected seasonally, including a new Antarctic minke whale bio-duck song sub-type described here for the first time. Antarctic minke and sei whales were more vocally active at night-time whereas the other species had no clear diel vocalizing patterns. Random forest models identified month and/or sea surface temperature as the most important predictors of all baleen whale acoustic occurrence. These novel results highlight the PEIs as a useful habitat for baleen whales given the number of species that inhabit or transit through this region.

The first record of the southbound movements of satellite‐tagged pygmy blue whales (B. m. brevicauda) from Savu Sea (Indonesia) to the subantarctic waters

The first record of the southbound movements of satellite‐tagged pygmy blue whales (<i>B. m. brevicauda</i>) from Savu Sea (Indonesia) to the subantarctic waters

BASSA: New software tool reveals hidden details in visualisation of low-frequency animal sounds.

The study of animal sounds in biology and ecology relies heavily upon time-frequency (TF) visualisation, most commonly using the short-time Fourier transform (STFT) spectrogram. This method, however, has inherent bias towards either temporal or spectral details that can lead to misinterpretation of complex animal sounds. An ideal TF visualisation should accurately convey the structure of the sound in terms of both frequency and time, however, the STFT often cannot meet this requirement. We evaluate the accuracy of four TF visualisation methods (superlet transform [SLT], continuous wavelet transform [CWT] and two STFTs) using a synthetic test signal. We then apply these methods to visualise sounds of the Chagos blue whale, Asian elephant, southern cassowary, eastern whipbird, mulloway fish and the American crocodile. We show that the SLT visualises the test signal with 18.48%-28.08% less error than the other methods. A comparison between our visualisations of animal sounds and their literature descriptions indicates that the STFT's bias may have caused misinterpretations in describing pygmy blue whale songs and elephant rumbles. We suggest that use of the SLT to visualise low-frequency animal sounds may prevent such misinterpretations. Finally, we employ the SLT to develop 'BASSA', an open-source, GUI software application that offers a no-code, user-friendly tool for analysing short-duration recordings of low-frequency animal sounds for the Windows platform. The SLT visualises low-frequency animal sounds with improved accuracy, in a user-friendly format, minimising the risk of misinterpretation while requiring less technical expertise than the STFT. Using this method could propel advances in acoustics-driven studies of animal communication, vocal production methods, phonation and species identification.

Predicting suitable habitats for foraging and migration in Eastern Indian Ocean pygmy blue whales from satellite tracking data

BackgroundAccurate predictions of animal occurrence in time and space are crucial for informing and implementing science-based management strategies for threatened species.MethodsWe compiled known, available satellite tracking data for pygmy blue whales in the Eastern Indian Ocean (n = 38), applied movement models to define low (foraging and reproduction) and high (migratory) move persistence underlying location estimates and matched these with environmental data. We then used machine learning models to identify the relationship between whale occurrence and environment, and predict foraging and migration habitat suitability in Australia and Southeast Asia.ResultsOur model predictions were validated by producing spatially varying accuracy metrics. We identified the shelf off the Bonney Coast, Great Australian Bight, and southern Western Australia as well as the slope off the Western Australian coast as suitable habitat for migration, with predicted foraging/reproduction suitable habitat in Southeast Asia region occurring on slope and in deep ocean waters. Suitable foraging habitat occurred primarily on slope and shelf break throughout most of Australia, with use of the continental shelf also occurring, predominanly in South West and Southern Australia. Depth of the water column (bathymetry) was consistently a top predictor of suitable habitat for most regions, however, dynamic environmental variables (sea surface temperature, surface height anomaly) influenced the probability of whale occurrence.ConclusionsOur results indicate suitable habitat is related to dynamic, localised oceanic processes that may occur at fine temporal scales or seasonally. An increase in the sample size of tagged whales is required to move towards developing more dynamic distribution models at seasonal and monthly temporal scales. Our validation metrics also indicated areas where further data collection is needed to improve model accuracy. This is of particular importance for pygmy blue whale management, since threats (e.g., shipping, underwater noise and artificial structures) from the offshore energy and shipping industries will persist or may increase with the onset of an offshore renewable energy sector in Australia.

Heard off Heard: Acoustic detections of sperm whales (Physeter macrocephalus) and other cetaceans off Heard Island.

An underwater acoustic recorder was moored off Heard Island from September 2017 through March 2018 to listen for marine mammals. Analysis of data was initially conducted by visual inspection of long-term spectral averages to reveal sounds from sperm whales, Antarctic and pygmy blue whales, fin whales, minke whales, odontocete whistles, and noise from nearby ships. Automated detection of sperm whale clicks revealed they were seldom detected from September through January (n = 35 h) but were detected nearly every day of February and March (n = 684 h). Additional analysis of these detections revealed further diel and demographic patterns.

Variational Mode Decomposition-Based Identification of Pygmy Blue Whales Song Units

Variational Mode Decomposition-Based Identification of Pygmy Blue Whales Song Units

Whale detection and microseismic monitoring via DAS using submarine telecommunications cables – a case study from the NWS, Western Australia

A monitoring trial of subsea distributed acoustic sensing (DAS) conducted in the marine waters of Australia is presented. This trial explores the concept of repurposing existing submarine telecommunications cables for remote monitoring of the environment and geophysical phenomena. The data were collected from a pre-existing fibre-optic cable, 50 km in length, that links two offshore hydrocarbon production platforms off the northwest coast of Australia. Initial data analyses confirmed the ability to detect underwater sounds from various sources, including marine animals (such as baleen whales), anthropogenic activities (such as vessels), and natural geophysical phenomena (such as earthquakes). The study underscores the efficacy of DAS for capturing and locating marine mammal vocalisations, specifically highlighting signals from pygmy blue whales – a species granted the highest protection status in Australia – and Omura’s whales, both of which migrate biannually through the offshore waters of Western Australia. These findings indicate the potential of subsea DAS for detecting and tracking marine fauna regionally. Moreover, they suggest its applicability for future monitoring in support of environmental impact assessments and the development of adaptive management strategies to prevent or minimise impacts on migratory whale species from offshore industries.

Comparatively poorer body condition of south-east Indian Ocean pygmy blue whales on their southern migration

The south-east Indian Ocean population of pygmy blue whales (Balaenoptera musculus brevicauda) forages in habitats between temperate foraging grounds off southern Australia and breeding grounds in Indonesian waters. With the opportunity to forage during migration, limited seasonal variation in body condition would be expected. However, increasing numbers of individuals in poor body condition with prominent spinal columns and other features of emaciation have been sighted during their southern migration. This study aimed to measure the morphology and body condition (relative body volume to body length) of pygmy blue whales during their northbound and southbound migration. Unmanned aerial vehicles were used to obtain images of 42 pygmy blue whales (one calf, five juveniles and 36 adults, including one lactating female) in 2021 and 2022. The body lengths ranged from 15.32 to 24.32 m, and the mean relative head length, length to blowhole, width of eyes, fluke width and length of peduncle were 21.8, 18.1, 12.8, 22.9 and 21.3% respectively. There was a significant decrease in body condition of 15.3% between north and southern migrating adult whales. Given the importance of body condition for reproductive success, understanding if this loss is due to natural seasonal variation, or habitat or prey disturbance from environmental environmental or anthropogenic sources, has implications for the future management of the species.

Do Whales Sing to Their Own Tune? Comparing the Variability Within and Between Song Events of the Eastern Indian Ocean Pygmy Blue Whale

Do Whales Sing to Their Own Tune? Comparing the Variability Within and Between Song Events of the Eastern Indian Ocean Pygmy Blue Whale

Pygmy Blue Whale Home Ranges and Their Overlaps with Indonesian and Australian Marine Protected Areas: Comparison between a-LoCoH and BBMM Methods

Information on the distribution of marine migratory species is lacking, and for a long time, these species have been overlooked in the designation of Marine Protected Areas (MPAs). This study analysed the home range of pygmy blue whales (PBWs) from western Australia to eastern Indonesia to be able to assess the overlap with current MPAs. In this study, data from 11 individual PBWs tagged in the Perth Canyon were used. Two home range methods, adaptive Local Convex Hull (a-LoCoH) and Brownian Bridge Movement Model (BBMM), were performed and compared to identify core use areas and connections between these areas (i.e., migration corridors). By assessing the relative properties and visually inspecting the home ranges, 90% BBMM (home range and migration corridor) and 50% BBMM (core use area) are chosen as the best results, because they cover the connected core-use areas to a large extent. The home ranges that were covered by current MPAs were only 2% in Indonesia and 16% in Australia. Important migration corridors without current protection are in the east Savu Sea, south of Timor Island, and wider Banda Sea. It is noteworthy that comparing methods is relevant to be able to choose the most suitable method for the data used and the goal of this study. The limited overlap between the calculated home ranges and the MPAs of the Indonesian waters articulates the importance of in-depth scientific studies to be able to evaluate, implement and develop marine conservation planning.

Tracking pygmy blue whales in the Perth Canyon using passive acoustic observatories

Eastern Indian Ocean pygmy blue (EIOPB) whales were localised and tracked through the Perth Canyon area utilising a passive acoustic tracking array. Vocalising animals were tracked using the Type II unit of the EIOPB whale song across recordings for an average of 109.3 min (95% CI ± 27 min), suggesting that animals move slowly through the array area. Comparisons of the distribution of animals between sample years revealed non-uniform distribution of animals suggesting that environmental variables may drive pygmy blue whale spatial distribution within foraging areas. Analysis of the movement patterns of acoustically tracked animals found that animals tracked between January and early March generally exhibited directional movement while singing animals tracked between March and May exhibited directional and milling movement patterns, indicating that they may be foraging, and thus that animals may sing between feeding bouts. Comparisons of visual and acoustic localisations found animals appeared to utilise similar areas around the passive acoustic receiver array on days where survey effort overlapped, though acoustic survey methods returned consistently higher numbers of detections. Further, acoustic and visual detections of animals within the same day were not within the same location highlighting the need for holistic studies of species habitat utilisation. The inclusion of in-situ environmental data collection in the design of future acoustic tracking studies would be valuable to understand whether there is a link between environmental factors at the local scale and the localised movement of whales around the listening area.

Offshore industry and whales: Pygmy blue whale acoustic behavior and movement patterns in the Otway Basin

The offshore Otway region of Australia is designated as a Biologically Important Area for foraging for blue whales. Understanding the acoustic behavior of blue whales in these foraging grounds will enable an improved understanding of the residency time of individual animals and facilitate improved management of the population. JASCO deployed a directional AMAR G4 for part of the 2020 pygmy blue whale foraging season. The recorded vocalizations, including song and D-calls, have been analyzed in detail to determine bearings, received level, and estimated ranges. Bearings to detected vocalizations were determined using a maximum-likelihood-estimator, with a fluid only propagation model corrected for the layered elastic seafloor used to determine ranges. An analysis of the distribution of different vocalizations across the listening range of the AMAR over time has been conducted and correlated with AIS information from shipping traffic. The results have been used to provide a brief insight into the acoustic behavior and movement patterns of individual pygmy blue whales within the region, furthering our understanding of spatial habitat use in association with commercial shipping lanes and oil and gas operations.

Variability in Temporal Characteristics of the South Eastern Indian Ocean Pygmy Blue Whale Song

The temporal characteristics of whale song are considered to be amongst the most stable elements of song production, though very few studies have looked at the timing of discrete sounds or the silences between them. This study indicates that the temporal characteristics of the song of the southeast Indian Ocean pygmy blue (SEIOPB) whale are highly variable. While the song repetition interval, or inter-song interval (ISI), appeared to remain consistent within a song event, defined as a consistent bout of singing presumed to come from an individual animal, it was found to be variable between song events. Song structure was a confounding factor in the analysis of variability in ISI with songs comprised of longer phrases naturally having a longer song repetition interval. The songs of the SEIOPB whale are characteristic of the species with only three primary song types. The three-unit song (units I, II and III) has the longest mean ISI of ~ 200 s, approximately twice that of songs composed of only two units (II and III) at a mean of ~ 100 s ISI which is approximately twice the ISI of a one-unit song (unit II only). The results of this study suggest that variability in ISI cannot be attributed to change in one element of a song but is driven by temporal changes in all elements of the song including phrase structure, unit duration and the length of the intervals between song units. Thus, the temporal characteristics of blue whale song appear to be under the control of the animal and may vary between individual whales, and within songs of an individual. It is concluded that the temporal characteristics of song potentially encode contextual information about the singer and may be influenced by audience effects, including audience composition and singer density.

Cetacean sightings around the Republic of the Maldives, April 1998

In April 1998, as part of a project to collect biopsy samples of putative pygmy blue whales (Balaenoptera musculus brevicauda) in the waters around the Republic of the Maldives, Indian Ocean, incidental sightings of cetaceans encountered were recorded. Using modified line-transect methods and handheld binoculars, a total of 267 sightings of 16 species of whales and dolphins were recorded during 20 at-sea days in the northeastern part of the atoll. Significant results include the following: (1) cetaceans were abundant and species diversity was high, including nearly every pantropical species of pelagic cetacean; (2) the spinner dolphin (Stenella longirostris) was by far the most common species encountered (56 sightings) and also had the largest mean school size ( = 50.3 individuals); (3) blue whales were rare; only four individuals were sighted; (4) a large concentration of Bryde’s whales (28 sightings in two days) was apparently feeding in nearshore waters; (5) this paper reports the first records for the Maldives of Cuvier’s beaked whale (Ziphius cavirostris), Blainville’s beaked whale (Mesoplodon densirostris) and the dwarf sperm whale (Kogia sima): the latter was particularly common (17 sightings); (6) the spotted dolphin (Stenella attenuata) was rare and almost always associated with yellowfin tuna (Thunnus albacares), spinner dolphin, or seabirds, as has been reported in the eastern Pacific and western Indian oceans.

A blue whale (Balaenoptera musculus) feeding ground in a southern Australian coastal upwelling zone

A localised aggregation of blue whales, which may be pygmy blue whales (B. m. brevicauda), occurs in southern Australian coastal waters (between 139°45AE-143°E) during summer and autumn (December-May), where they feed on coastal krill (Nyctiphanes australis), a species which often forms surface swarms. While the abundance of blue whales using this area is unknown, up to 32 blue whales have been sighted in individual aerial surveys. Krill appear to aggregate in response to enhanced productivity resulting from the summer-autumn wind-forced Bonney Coast upwelling along the continental shelf. During the upwelling’s quiescent (winter-spring) period, blue whales appear to be absent from the region. Krill surface swarms have been associated with 48% of 261 blue whale sightings since 1998, with direct evidence of feeding observed in 36% of all sightings. Mean blue whale group size was 1.55 (SD = 0.839), with all size classes represented including calves. This seasonally predictable upwelling system is evidently a regular feeding ground for blue whales, and careful management of human activities is required there.

The abundance of blue whales on the Madagascar Plateau, December 1996

As part of the International Whaling Commission’s SOWER blue whale research programme, two sighting vessels, the Shonan Maru and the Shonan Maru No.2, surveyed the Madagascar Plateau between 25° and 35°S, 40° and 45°E, in December 1996. A total of 95 sightings of 110 blue whales (assigned in the field as pygmy blue whales – see discussion), 14 sightings of 21 blue whales (subspecies undetermined) and 12 sightings of 13 ‘like blue’ whales was made in 23 days. In the first half of the survey, the whole research area was covered in a mainly pre-determined zigzag search pattern, and the associated sightings and effort have been used to derive density estimates for blue whales for the area. Sightings in the second half of the survey, where effort was directed at blue whale concentrations, have only been used to provide supplementary data for calculation of the effective search half-width and mean school size. The resulting population estimate is 424 (CV = 0.42), or 472 (CV = 0.48) whales when ‘like blue’ sightings are included. Dive times and surfacing behaviour recorded in just over 21h of monitoring suggest that the assumption that all groups on the trackline were seen (g(0) = 1) is reasonable. As the geographical extent of the survey area was substantially less than that of past catches of blue whales in the region in December, this estimate must refer to only a portion (possibly about one third) of the total population. Some evidence of feeding on euphausiids in the region was detected, possibly as a consequence of a localised upwelling cell at the southern tip of Madagascar.

La Niña conditions influence interannual call detections of pygmy blue whales in the eastern Indian Ocean

Oceans across the globe are warming rapidly and marine ecosystems are changing as a result. However, there is a lack of information regarding how blue whales are responding to these changing environments, especially in the Southern Hemisphere. This is because long term data are needed to determine whether blue whales respond to variability in environmental conditions. Using over 16 years of passive acoustic data recorded at Cape Leeuwin, we investigated whether oceanic environmental drivers are correlated with the migration patterns of eastern Indian Ocean (EIO) pygmy blue whales off Western Australia. To determine which environmental variables may influence migration patterns, we modelled the number of acoustic call detections of EIO pygmy blue whale calls with broad and fine scale environmental variables. We found a positive correlation between total annual whale call detections and El Niño Southern Oscillation (ENSO) cycles and the Indian Ocean Dipole (IOD), with more whale calls detected during La Niña years. We also found that monthly whale call detections correlated with sea surface height around the hydrophone and chlorophyll-a concentration at a prominent blue whale feeding aggregation area (Bonney Upwelling) where whales feed during the summer before migrating up the west Australian coast. At the interannual scale, ENSO had a stronger relationship with call detections than IOD. During La Niña years, up to ten times more EIO pygmy blue whale calls were detected than in neutral or El Niño years. This is likely linked to changes in productivity in the feeding areas of the Great Australian Bight and Indian Ocean. We propose that in lower productivity years whales either skipped migration or altered their habitat use and moved further offshore from the hydrophones and therefore were not detected. The frequency and intensity of ENSO events are predicted to increase with climate change, which is likely to impact the productivity of the areas used by blue whales. These changes in productivity may affect the physical condition and reproductive success of individual whales. A reduction in reproductive success could have a significant impact on blue whale recovery from historical whaling and their ability to adapt to a changing environment.

Vocalisations of Antarctic blue whales, Balaenoptera musculus intermedia, recorded during the 2001/2002 and 2002/2003 IWC/SOWER circumpolar cruises, Area V, Antarctica

Blue whale vocalisations recorded during the 2001/2002 and 2002/2003 International Whaling Commission-Southern Ocean Whale and Ecosystem Research (IWC/SOWER) cruises were analysed to determine the feasibility of using acoustic recordings for sub-species identification of the Antarctic blue whale (Balaenoptera musculus intermedia) and the pygmy blue whale (B.m. brevicauda). The research was conducted in IWC Area V, from latitude 60°S to the ice edge and between longitudes 130°E and 150°E on the Shonan Maru (2001/2002), and between 150°E and 170°W on the Shonan Maru No.2 (2002/2003). Data including 15 groups consisting of 42 animals, as well as opportunistic recordings of an unknown number of animals during evening sonobuoy stations were examined for this study. Vocalisations included long-duration 28Hz tonal sounds and relatively short-duration frequency-modulated sounds. The short-duration calls were similar to vocalisations recorded in the presence of blue whales in other locations worldwide. Not all recordings contained the longduration 28Hz call, considered to be a species-specific vocalisation of Antarctic blue whales. None of the sounds that have previously been attributed to pygmy blue whales were detected. The long-duration 28Hz tonal vocalisations included 3-unit calls, considered to be song phrases, as well as simple 28Hz sounds and 28Hz sounds followed by a downsweep. The centre and peak frequencies of the 28Hz tone for these three sound types were stable regardless of signal strength; however, for the 3-unit vocalisation, the presence and characteristics of their 2nd and 3rd units were variable. Examination of two distinct groups of simultaneously vocalising blue whales showed no evidence of temporally repeated patterns of vocalisations (song phrases). The results of this study suggest that the peak frequency of the 28Hz vocalisations may be used as a diagnostic feature to aid in discriminating between Antarctic blue whales and pygmy blue whales in the field; however, examination of vocalisations in relation to group size and behaviour are necessary to understand the circumstances in which the 28Hz vocalisations are produced.

Patterns of genetic variation in Southern Hemisphere blue whales and the use of assignment test to detect mixing on the feeding grounds

A total of 111 samples from Southern Hemisphere blue whales were sequenced for 420 base pairs of the mitochondrial control region and all but one of those were genotyped over seven microsatellite loci. Comparisons were made between samples from three broad geographic regions: the southeast Pacific Ocean; Indian Ocean; and around the Antarctic continent. Each of these strata was found to be highly differentiated from the others, in both mitochondrial and nuclear data. The genetic differentiation between the geographic ranges of the nominal subspecies (i.e. true blue whales in Antarctica vs. pygmy blues in Pacific and Indian Oceans) was not markedly greater than between the populations of pygmy blue whales. Assignment tests using the microsatellite data provide some insight into detection of feeding-season mixing, although existing methods have some limitations.