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(a) Bathymetry and mean location of major oceanographic features in the study area (see text for details). From north to south: CRD, Costa Rica Dome; EF, Equatorial Front; NSTF, North Subtropical Front; AgCF, Agulhas Current Front; SSTF, South Subtropical Front; SAF, Subantarctic Front; APF, Antarctic Polar Front; SACCF, Southern Antarctic Circumpolar Current Front. (b) Annual mean phytoplankton chlorophyll- a concentrations in mg.m - 3 from SeaWiFS (4 September 1997–30 September 2006). (c) Catches of blue whales in the International Whaling Commission database grouped into 1° ¥ 1° squares. Catches from land stations were generally all assigned to the same square.
Source publication
Blue whale locations in the Southern Hemisphere and northern Indian Ocean were obtained from catches (303,239), sightings (4,383 records of ≥8,058 whales), strandings (103), Discovery marks (2,191) and recoveries (95), and acoustic recordings. 2. Sighting surveys included 7,480,450 km of effort plus 14,676 days with unmeasured effort. 3. Groups usu...
Contexts in source publication
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... IWC catch database includes catch positions for 303 329 blue whales (and individual data for 311 948 whales in all) in the study area, i.e. 83.6% of the estimated 362 879 blue whales caught in this region (Branch et al., 2004). Figure 1 shows the distribution of the catch and the major environmental features of the study area, although treatment of the association between the latter and blue whale distribution is left for the Discussion section. Catches covered the Antarctic densely. ...
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... (one group every 2200 km), but are obviously biased upwards because most studies focused on high-density blue whale areas and many studies that reported no blue whales were excluded. For large-scale surveys with dedicated cetacean effort and good sighting platforms, sighting rates varied by more than four orders of mag- . Sources are the same as Fig. 1. Bottom panel: proportion of large cetacean catches in each 2° ¥ 2° square that were blue whales. 126 T. A. Branch et al. nitude from region to region. When ordered, these sighting rates (groups per 1000 km) are as follows: off Costinha, Brazil, 0.003 (da Rocha, 1983); off Durban, South Africa, 0.005 from spotter planes (P. B. Best, ...
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... blue whales were present, this was often confirmed by multiple sources (Fig. 10). For example, although there were only rare detections of blue whales off northern New Zealand, these records included catches, sightings, strandings and acoustic ...
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... positional data were recorded during the austral summer season between October and April ( Fig. 11). During summer, records were nearly circumpolar especially between Novem- ber and March. The Antarctic region between 160°W and 70°W was hardly exploited ...
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... recorded in temperate latitudes off the west coast of South America, in the northern Indian Ocean, in the Subantarctic, around southern Australia and in north-west New Zealand, but were largely absent from African waters. In winter months (April-September), high catches were reported off south-west Africa (especially Saldanha Bay), and Durban (Fig. 12). In these months, sightings and strandings continued in other areas. It is also notable that catches were reported in every month of the year at South Georgia, although numbers (and catch effort) decreased greatly in the winter ...
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... whale distribution in the study area is strongly linked to latitude. Close to the Antarctic, blue whales were recorded along bands stretching across entire ocean basins, but at lower latitudes they are progressively more clustered, localized and compressed along the continental margins ( Fig. 10). This pattern probably reflects euphausiid biogeography, with large Antarc- tic krill Euphausia superba at the highest latitudes, mid-sized Euphausia species in the mid latitudes and smaller Nyctiphanes species in coastal upwelling systems in the mid and low latitudes (see maps in Brinton et al., 2000). However, until better ...
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... and merging, meandering, and eddy shedding, often result in front-associated phy- toplankton blooms (Moore & Abbott, 2000). Antarctic catches were bounded to the north by the Antarctic Polar Front, and pygmy blue whale distribution in the Subantarctic was fairly well bounded by the Subantarctic Front and the North and South Subtropical Fronts (Fig. 1). Off the west coasts of South America and Africa, distribution extended from upwelling regions to the Equatorial Front. Blue whales south of Madagascar may be sup- ported by biological enrichment from the interaction of the North Subtropical Front with the steep bathymetry of the Madagascar Plateau; interactions of this front with the ...
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... whales are largely absent from the central portions of each of the major ocean basins in the study area, which are notable biological deserts, as evidenced by the very low chlorophyll-a concentrations in these regions ( Fig. 1; McClain, Signorini & Christian, ...
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... ( Dalla Rosa & Secchi, 1997). It is a mystery why there are so few blue whale records from this region despite intensive whaling and sighting effort (Figs 3 and 6; da Rocha, 1983), especially given its extensive use by other large cetaceans ( Zerbini et al., 1997;Croxall & Wood, 2002;Reyes, 2006) and areas of high chlorophyll-a concentrations ( Fig. 1b; Romero et al., 2006). However, it is worth noting that the high chlorophyll-a concentrations are over the broad continental shelf (Fig. 1a), which is probably shallower than the depths preferred by blue ...
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... effort (Figs 3 and 6; da Rocha, 1983), especially given its extensive use by other large cetaceans ( Zerbini et al., 1997;Croxall & Wood, 2002;Reyes, 2006) and areas of high chlorophyll-a concentrations ( Fig. 1b; Romero et al., 2006). However, it is worth noting that the high chlorophyll-a concentrations are over the broad continental shelf (Fig. 1a), which is probably shallower than the depths preferred by blue ...
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... has been suggested that northern Indian Ocean blue whales are a separate subspecies, B. m. indica (Blyth, 1859). While this name is accepted as valid, and has nomenclatural priority over both brevicauda (Ichihara, 1966) and intermedia (Burmeister, 1871), the distinguishing features (if any) of northern Indian Ocean blue whales are poorly known (Rice, 1998). It seems more likely that northern Indian Ocean and pygmy blue whales belong to the same subspecies, based on Soviet catches, where the mean length of sexually mature females from the northern Indian Ocean is 69 ft (21.0 m), nearly identical to that for pygmy blue whales from the southern Indian Ocean, and in contrast to the ~84 ft (25.6 m) from Antarctic catches (Branch et al., 2007). ...
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... Soviet catches, where the mean length of sexually mature females from the northern Indian Ocean is 69 ft (21.0 m), nearly identical to that for pygmy blue whales from the southern Indian Ocean, and in contrast to the ~84 ft (25.6 m) from Antarctic catches (Branch et al., 2007). On the other hand, their geographical distribution is fairly discrete (Fig. 10), and their breeding cycle is 6 months out of phase with those in the southern Indian Ocean (Mikhalev, 2000, p. 151). It is noteworthy that a resident population of humpback whales in the northern Indian Ocean (particularly the Arabian Sea) also has a reproductive cycle shifted by 6 months compared with the Southern Hemisphere ...
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... in southern Chilean waters during the summer when Antarctic blue whales should be in polar waters (Hucke-Gaete et al., 2003). Finally, there was a distinct gap between the southernmost sightings at 44°S and the northernmost Antarctic records at 64°S, corresponding to the region between the South Subtropical Front and the Antarctic Polar Front (Fig. ...
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... pygmy blue whales recorded south of Madagascar appear to move southwards and spread longitudinally in the southern Indian Ocean in the summer. In January through March, pygmy blue whales are distributed almost continuously in the Subantarctic between Africa and Australia (Fig. 11). The call type recorded south of Madagascar in December was recorded in Diego Garcia (6°18′S 71°E) in May-July (Stafford et al., 2005), suggesting a northern migration in ...
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... Australia and Indonesia, the monthly data suggest a migratory link between Australia and Indonesia around the western coast of Australia. As shown in Figs 11 and 12, blue whales have been recorded in Indonesian waters during May to November while high concentrations are reported from the southern coast of Australia mostly during the austral summer (November to May). Acoustic detections off West Australia (21°S) record blue whales apparently migrating northwards in June-July and southwards in November- December (R. D. McCauley, unpublished data). ...
Similar publications
Surveys were conducted off the southern coast of Sri Lanka in 2014 and 2015 to investigate
the distribution patterns of blue whales (Balaenoptera musculus spp.) in relation to current
shipping lanes, and further offshore. There have been several reported ship strikes of blue
whales in this area and the IWC Scientific Committee has recognised the po...
Citations
... Many baleen whale species and populations are endangered, following the 20 th century industrial whaling. For instance, as the largest animals in the world, blue whales (Balaenoptera musculus) were targeted by whalers, with only 0.15% of the Southern Hemisphere population surviving commercial whaling (Branch et al., 2007;Thomas et al., 2016). Large baleen whales such as blue whales have few natural predators and feed on prey at low trophic levels, occupying a rare niche with few other species. ...
... Thus, if global change that leads to their loss occurs, it is unlikely that they could be easily replaced within the food web. Furthermore, their longdistance migration behaviour requires considerable energy (Branch et al., 2007). Thus, large baleen whales require predictable and high-energy food sources for the few months they feed. ...
... Mean chlorophyll-a was calculated for each year and both seasons (December to May; June to November). One potential caveat is that the measurement of the chlorophylla was from the water surface, hence the data may not reflect krill density in deep water (Branch et al., 2007). ...
Marine ecosystems are experiencing rapid shifts under climate change scenarios and baleen whales are vulnerable to environmental change, although not all impacts are yet clear. We identify how the migration behaviour of the Chagos whale, likely a pygmy blue whale (Balaenoptera musculus brevicauda), has changed in association with shifts in environmental factors. We used up to 18 years of continuous underwater acoustic recordings to analyse the relationships between whale acoustic presence and sea surface temperature (SST), chlorophyll-a concentration, El-Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). We compared these relationships between two independent sites Diego Garcia southeast (DGS) and Diego Garcia northwest (DGN) where Chagos whales are detected and are suspected to move interannually across the Chagos-Laccadive ridge. We showed that the number of whale songs detected increased on average by 7.7% and 12.6% annually at DGS and DGN respectively. At the DGS site, Chagos whales shifted their arrival time earlier by 4.2 ± 2.0 days/year ± SE and were detected for a longer period by 7.3 ± 1.2 days/year ± SE across 18 years. A larger number of songs were detected during periods of higher chlorophyll-a concentration, and with positive IOD phases. At the DGN site, we did not see an earlier shift in arrival and songs were not detected for a longer period across the 13 years. Whale presence at DGN had a weaker but opposite relationship with chlorophyll-a and IOD. The oceanic conditions in the Indian Ocean are predicted to change under future climate scenarios and this will likely influence Chagos whale migratory behaviour. Understanding how environmental factors influence whale movement patterns can help predict how whales may respond to future environmental change. We demonstrate the value of long-term acoustic monitoring of marine fauna to determine how they may be affected by changing environmental conditions.
... In many mammalian species, including elephants [102], pinnipeds [103] and ungulates [104][105][106][107], the limitation or cessation of food consumption by males during the breeding season is common-the motivation for which appears to be the reduction of foraging time in favour of breeding efforts. While it has previously been accepted that both sexes of several baleen whale species also limit food intake during their annual migrations to breeding grounds [89], blue whales may exhibit both foraging and reproductive behaviours on their low-latitude breeding grounds [108,109]. Therefore, it is also possible that multiple behavioural states may also be exhibited at feeding sites. Although southern California is primarily considered to be a seasonal feeding ground for blue whales, our analysis indicates a temporal separation between two behavioural states for blue whales in this region: individuals may begin feeding as early as spring, continuing through summer until the autumn, at which time reproductive behaviours begin to dominate. ...
Acoustic communication is an important aspect of reproductive, foraging and social behaviours for many marine species. Northeast Pacific blue whales (Balaenoptera musculus) produce three different call types—A, B and D calls. All may be produced as singular calls, but A and B calls also occur in phrases to form songs. To evaluate the behavioural context of singular call and phrase production in blue whales, the acoustic and dive profile data from tags deployed on individuals off southern California were assessed using generalized estimating equations. Only 22% of all deployments contained sounds attributed to the tagged animal. A larger proportion of tagged animals were female (47%) than male (13%), with 40% of unknown sex. Fifty per cent of tags deployed on males contained sounds attributed to the tagged whale, while only a few (5%) deployed on females did. Most calls were produced at shallow depths (less than 30 m). Repetitive phrasing (singing) and production of singular calls were most common during shallow, non-lunging dives, with the latter also common during surface behaviour. Higher sound production rates occurred during autumn than summer and they varied with time-of-day: singular call rates were higher at dawn and dusk, while phrase production rates were highest at dusk and night.
... Of global interest are habitats important to pygmy blue whales (Balaenoptera musculus brevicauda), a subspecies that has not fully recovered from exploitation and still faces threats, such as ship strikes, incidental catch and oil and gas development (Clapham et al., 1999;CSIRO, 2007;Tournadre, 2014). Based off historic catch distributions (Branch et al., 2007) and, more recently, by satellite tag tracking data (Gales et al., 2010;Double et al., 2014), pygmy blue whales are indicated to be in the vicinity of the Browse Basin. Understanding the distribution of pygmy blue whales and other cetaceans in the Browse Basin is needed given their important role in impacting marine ecosystems, e.g. ...
There is an increasing demand for integrated pelagic surveys to support ecosystem-based management of marine environments and their associated marine life. The Browse Basin in the tropical eastern Indian Ocean was surveyed using ship line transects to determine habitat associations of cetaceans and seabirds with submarine topography and local oceanographic conditions during winter and spring 2008. Fourteen species of cetaceans, including the data deficient pygmy blue whale, and 23 species of seabirds were encountered throughout the basin. Aggregations of both cetaceans and seabirds were observed at two significant submarine topographic features, Scott Reef and Browse Cliffs, particularly during spring when encounters and abundances of odontocetes were far greater. The attraction of cetaceans and seabirds to Scott Reef and Browse Cliffs was likely foraging-related given these features were associated with upwelling and elevated biomass of krill and fish. Sub-mesoscale sea surface temperature and chlorophyll a fronts also occurred in vicinity to Browse Cliffs and the shelf environment. The Browse Basin is an important, and potentially predictable, foraging ground for a variety of top predators, and their occurrence would have implications for the current and future management practices of oil and gas industries operating in the region.
... A number of their areas of aggregation have been identified, including waters near Somalia ( Small and Small, 1991), the Seychelles ( Mikhalev, 2000), the Maldives ( Ballance et al., 2001;Anderson, 2005), and Sri Lanka (de Vos et al., 2014a). Sighting, stranding and acoustic data ( Alling et al., 1991;Ilangakoon, 2006;Branch et al., 2007;Afsal et al., 2008;de Vos et al., 2012) indicate that this population occupies Sri Lankan waters almost year round. Off southern Sri Lanka, groups of NIO blue whales have been observed engaging in breeding activity (specifically "ménage à trois" behaviors as described by Sears et al., 2009). ...
Blue whales are little studied, face significant anthropogenic threats and within the Northern Indian Ocean, have a restricted range, making them an archetype for conservation needs of megafauna around the world. We studied feeding behavior of blue whales using dietary DNA metabarcoding of fecal samples. While globally blue whale populations feed predominantly on Euphausiidae, 87% of prey DNA amplicons extracted from fecal samples from this population were sergestid shrimp, demonstrating that blue whales can locate and feed on dense swarms of other types of prey when they occur. Within the Indian Ocean sergestids are present within the top 300 m, which correlates with the deep scattering layer observed by hydroacoustics. Studies suggest that this requirement to dive deeper in search of prey likely explains the prevalence of fluke up diving within this population of blue whales relative to other parts of the globe. Furthermore, this study revealed the presence of acanthocephalan endoparasites within the stomach and intestines of the Northern Indian Ocean blue whales. This represents the first record of Acanthocephala in blue whales in the Northern Indian Ocean and highlights the need for further studies on both the ecto- and endoparasitic flora and monitoring of health of these cetaceans for their management and conservation.
... During this migration the species also uses other transitory areas to feed, such the Frontal System off Baja California [20]. Blue whales from the Southern Hemisphere forage in the southern Humboldt Current System and the Antarctic Circumpolar Current in summerautumn [21]. Some of them migrate in winter-spring to the northern Humboldt Current System [21,22], and the Equatorial Cold Tongue [23] for breeding. ...
... Blue whales from the Southern Hemisphere forage in the southern Humboldt Current System and the Antarctic Circumpolar Current in summerautumn [21]. Some of them migrate in winter-spring to the northern Humboldt Current System [21,22], and the Equatorial Cold Tongue [23] for breeding. Although blue whales have been recorded year-round at the Costa Rica Dome, it is not clear whether those animals come from both hemispheres, or if at least some belong to a resident population [24]. ...
... They migrate to mid and low latitudes during the summer-autumn of the Northern Hemisphere (i.e. winter-spring of the Southern Hemisphere) to reproduce and feed [21]. Therefore, we would expect that the higher whale densities during this period are concentrated in the South Equatorial Countercurrent and the northern Humboldt Current System, where higher temperatures would be more suitable for calving and where prey aggregations remain high. ...
We inferred the population densities of blue whales (Balaenoptera musculus) and short-beaked common dolphins (Delphinus delphis) in the Northeast Pacific Ocean as functions of the water-column’s physical structure by implementing hierarchical models in a Bayesian framework. This approach allowed us to propagate the uncertainty of the field observations into the inference of species-habitat relationships and to generate spatially explicit population density predictions with reduced effects of sampling heterogeneity. Our hypothesis was that the large-scale spatial distributions of these two cetacean species respond primarily to ecological processes resulting from shoaling and outcropping of the pycnocline in regions of wind-forced upwelling and eddy-like circulation. Physically, these processes affect the thermodynamic balance of the water column, decreasing its volume and thus the height of the absolute dynamic topography (ADT). Biologically, they lead to elevated primary productivity and persistent aggregation of low-trophic-level prey. Unlike other remotely sensed variables, ADT provides information about the structure of the entire water column and it is also routinely measured at high spatial-temporal resolution by satellite altimeters with uniform global coverage. Our models provide spatially explicit population density predictions for both species, even in areas where the pycnocline shoals but does not outcrop (e.g. the Costa Rica Dome and the North Equatorial Countercurrent thermocline ridge). Interannual variations in distribution during El Niño anomalies suggest that the population density of both species decreases dramatically in the Equatorial Cold Tongue and the Costa Rica Dome, and that their distributions retract to particular areas that remain productive, such as the more oceanic waters in the central California Current System, the northern Gulf of California, the North Equatorial Countercurrent thermocline ridge, and the more southern portion of the Humboldt Current System. We posit that such reductions in available foraging habitats during climatic disturbances could incur high energetic costs on these populations, ultimately affecting individual fitness and survival.
... Antarctic blue whales primarily filter feed on zooplankton prey, chiefly Antarctic krill (Euphausia superba) (Best, 2007; Branch et al., 2007). Little or no feeding is thought to occur during winter migrations and their distribution during the austral summer is particularly determined by prey distribution (Best, 2007; Branch et al., 2007). ...
... Antarctic blue whales primarily filter feed on zooplankton prey, chiefly Antarctic krill (Euphausia superba) (Best, 2007; Branch et al., 2007). Little or no feeding is thought to occur during winter migrations and their distribution during the austral summer is particularly determined by prey distribution (Best, 2007; Branch et al., 2007). Year-round passive acoustic recordings show that Antarctic blue whales might be feeding on their breeding grounds and move in between regions in a season, possibly to make use of available food resources in those regions (Samaran et al., 2013). ...
... Figure 1: Multi-decadal patterns of catches (a) and abundance estimated by logistic models (b) of the Antarctic blue whale in the southern hemisphere showing the discovery, exploitation and subsequent collapse of the species (adapted from Branch et al., 2004). It is currently difficult from sighting surveys to monitor the population recovery of the Antarctic blue whale, which was so extensively decimated by commercial whaling (Branch et al., 2007). The difficulty with sighting surveys is that trained observers can only see Antarctic blue whales for a short period of time when these mammals surface to breathe, and those sighting surveys can only be done in adequate daylight during good weather conditions (Mellinger and Barlow, 2003; Thomas and Marques, 2012). ...
Marine mammals, and in particular Antarctic blue whales, represent an important predator component of marine ecosystems. These mammals are considered to be critically endangered due to unsustainable whaling practices in the previous century. Currently, it is also difficult to monitor the species’ population recovery through the use of sighting surveys. Passive acoustic monitoring (PAM) can be used to research Antarctic blue whales because they are quite vocal and can be detected over long distances through the use of this technology. PAM also has considerable application potential to other baleen species that reside in South African waters, including fin whales (Balaenoptera physalus). It is, however, still an emerging
methodology in South Africa and a number of challenges need to be addressed before it reaches the same level of maturity as visual surveys in South Africa and around the world.
... Seasonal high productivity in the Chiloense Ecoregion has been highlighted previously (Silva et al., 1997; Avaria et al., 2004; Hucke-Gaete, 2004; Viddi et al., 2010), as well as its potential (and vulnerability) as a major 'CO 2 sink' (Iriarte et al., 2010). This area also comprises the habitat of several fish and invertebrate species of economic importance and has been depicted as one of the most important blue whale (Balaenoptera musculus) feeding and nursing grounds in the entire Southern Hemisphere (Hucke-Gaete et al., 2004; Branch et al., 2007). The ecological role of large whales might be an important and largely overlooked missing piece in the puzzle of why some areas of the Patagonian fjords such as the Chiloense Ecoregion are highly productive, even more so than more northerly coastal upwelling areas (Hucke-Gaete, 2004). ...
1. Since 2000, an increasing number of humpback whale sightings have been recorded in northern Chilean Patagonia (mostly between 41.5�S and 44�S) from dedicated aerial and marine surveys and also opportunistic and land-based platforms during austral summer and autumn months.
2. Based on local knowledge from the early years of coastal whaling suggesting the historic presence of humpback whales in the area, and more recent observations confirming feeding groups, mother–calf pairs, and philopatry, it is proposed that a proportion of the eastern South Pacific humpback whales consistently use the Chiloe-Corcovado region to feed and nurse their young.
3. This mid-latitude area could be regarded as the northernmost feeding ground for humpback whales in South America, extending the previous known range some 1300km north.
4. These findings provide further evidence for alternative life-strategies other than traditional migration and highlight the importance of northern Patagonian fjords to resolve questions that are central for large baleen whale conservation and management such as the extent and characteristics of spatio-temporal habitat use and overlap with human activities.
5. The need for future research on the migratory movements and population structure of this poorly understood population of humpback whales is emphasized, while an account is given of the threats they currently face.
... Speculations on maturity could be flawed if more than one stock is present, including a possible small-sized fin whale, in line with Clarke's (2004) proposal. Evidence is mounting for a scenario similar to blue whale status in Peru (Van Waerebeek et al., 1997) where a small form, possibly distinct from the pygmy blue whale (Branch et al., 2007) occurs. Fin whales caught off Peru in 1961-1977 (Ramírez, 1988) seem to broadly agree with length composition in the 1928 catches, unfortunately Ramírez did not discuss sexual and physical maturity. ...
A summer sighting of a loose aggregation of 11 photo-identified fin whales off Callao (12°09.5'S,77°23.2'W), central Peru, on 3 March 2007 raised the issue of seasonality. However, 20th century whaling records off Peru confirmed year-round presence of fin whales. Whalers presumed most were juveniles due to their small size. The Callao fin whales were also smallish and showed a nondescript, dusky colouration without clear head blazes or chevrons. Clarke (2004) suggested the existence of a dark, small-bodied (‘pygmy’) fin whale, possibly with black baleen, in the Southern Hemisphere, he referred to as B. physalus patachonica. A critical reading of Burmeister’s (1865) description of B. patachonica points to an unusual combination of fin whale morphological features with others, including a nasal bone configuration, that do not match B. physalus. We recommend a re-examination of B. patachonica type specimens, besides fin whale biopsy sampling, photo-identification and sound recordings off Peru, Ecuador and northern Chile. The taxonomic position of Balaenoptera Tschudii Reichenbach, 1846 or ‘Peruvian finner’ (Gray, 1866) should also be revisited.
The study of marine soundscapes is a growing field of research. Recording hardware is becoming more accessible; there are a number of off-the-shelf autonomous recorders that can be deployed for months at a time; software analysis tools exist as shareware; raw or preprocessed recordings are freely and publicly available. However, what is missing are catalogues of commonly recorded sounds. Sounds related to geophysical events (e.g. earthquakes) and weather (e.g. wind and precipitation), to human activities (e.g. ships) and to marine animals (e.g. crustaceans, fish and marine mammals) commonly occur. Marine mammals are distributed throughout Australia’s oceans and significantly contribute to the underwater soundscape. However, due to a lack of concurrent visual and passive acoustic observations, it is often not known which species produces which sounds. To aid in the analysis of Australian and Antarctic marine soundscape recordings, a literature review of the sounds made by marine mammals was undertaken. Frequency, duration and source level measurements are summarised and tabulated. In addition to the literature review, new marine mammal data are presented and include recordings from Australia of Omura’s whales (Balaenoptera omurai), dwarf sperm whales (Kogia sima), common dolphins (Delphinus delphis), short-finned pilot whales (Globicephala macrorhynchus), long-finned pilot whales (G. melas), Fraser’s dolphins (Lagenodelphis hosei), false killer whales (Pseudorca crassidens), striped dolphins (Stenella coeruleoalba) and spinner dolphins (S. longirostris), as well as the whistles and burst-pulse sounds of Australian pygmy killer whales (Feresa attenuata). To date, this is the most comprehensive acoustic summary for marine mammal species in Australian waters.
We examined recordings from a 15-month (May 2009–July 2010) continuous acoustic data set collected from a bottom-mounted passive acoustic recorder at a sample frequency of 6 kHz off Portland, Victoria, Australia (38°33′01″S, 141°15′13″E) off southern Australia. Analysis revealed that calls from both subspecies were recorded at this site, and general additive modeling revealed that the number of calls varied significantly across seasons. Antarctic blue whales were detected more frequently from July to October 2009 and June to July 2010, corresponding to the suspected breeding season, while Australian blue whales were recorded more frequently from March to June 2010, coinciding with the feeding season. In both subspecies, the number of calls varied with time of day; Antarctic blue whale calls were more prevalent in the night to early morning, while Australian blue whale calls were detected more often from midday to early evening. Using passive acoustic monitoring, we show that each subspecies adopts different seasonal and daily call patterns which may be related to the ecological strategies of these subspecies. This study demonstrates the importance of passive acoustics in enabling us to understand and monitor subtle differences in the behavior and ecology of cryptic sympatric marine mammals.
