Pygmy blue whale movement, distribution and important areas in the Eastern Indian Ocean

This study was conducted as part of AIMS’ North West Shoals to Shore Research Program (NWSSRP) and was supported by Santos as part of the company’s commitment to better understand Western Australia’s marine environment. Hydrophone pressure data from Ocean Bottom Seismometers (OBS) were provided by the CANPASS project, jointly funded by the National Natural Science Foundation of China (NSFC grants 91955210, 41625016), and the China Academy of Science (CAS program GJHZ1776). Instruments were provided by the Australian National instrument pool ANSIR (http://ansir.org.au/). ANSIR, OBS data was also made data available from the Geoscience Australia and Shell. Data was sourced from Australia’s Integrated Marine Observing System (IMOS).Pygmy blue whales in the South-east Indian Ocean migrate from the southern coast of Australia to Indonesia, with a significant part of their migration route passing through areas subject to oil and gas production. This study aimed at improving our understanding of the spatial extent of the distribution, migration and foraging areas, to better inform impact assessment of anthropogenic activities in these regions. Using a combination of passive acoustic monitoring of the NW Australian coast (46 instruments from 2006 to 2019) and satellite telemetry data (22 tag deployments from 2009 to 2021) we quantified the pygmy blue whale distribution and important areas during their northern and southern migration. We show extensive use of slope habitat off Western Australia and only minimal use of shelf habitat, compared to southern Australia where use of the continental shelf and shelf break predominates. In addition, movement behaviour estimated by a state-space model on satellite tag data showed that in general pygmy blue whales off Western Australia were mostly engaged in migration, interspersed with mostly relatively short periods (median = 28hours, range = 2 – 1080hours) of low move persistence (slow movement with high turning angles), which is indicative of foraging. Using the spatial overlap of time and number of whales in area analysis of the satellite tracking data (top 50% of grid cells) with foraging movement behaviour, we quantified the spatial extent of pygmy blue whale high use areas for foraging and migration. We compared these areas to the previously described areas of importance to foraging and migrating whales (Biologically Important Areas; BIAs). In some cases these had good agreement with the most important areas we calculated from our data, but others had only low (5%) to moderate (13%) overlap. Month was the most important variable predicting the number of pygmy blue whale units and number of singers (acting as indices of pygmy blue whale density). Whale density was highest in the southern part of the NW Australian coast and whales were present there between April-June, and November-December, a pattern also confirmed by the satellite tracking data. Available data indicated pygmy blue whales spent up to 124 days in Indonesian waters (34% of annual cycle). Since this area may also be the calving ground for this population, inter-jurisdictional management is necessary to ensure their full protection.Publisher PDFPeer reviewe

Project BRAHSS: behavioural response of Australian humpback whales to seismic surveys.

BRAHSS is a major project aimed at understanding how humpback whales respond to noise, particularly from seismic air gun arrays. It also aims to infer the longer term biological significance of the responses from the results and knowledge of normal behaviour. The aim is to provide the information that will allow seismic surveys to be conducted efficiently with minimal impact on whales. It also includes a study of the response to ramp-up in sound level. Ramp-up is widely used at the start of operations as a mitigation measure intended to cause whales to move away, but there is little information to show that it is effective. BRAHSS involves four experiments with migrating humpback whales off the east and west coasts of Australia with noise exposures ranging from a single air gun to a full seismic array. Two major experiments have been completed off the east coast, the second involving 70 scientists. Whale movements were tracked using theodolites on two high points ashore and behavioural observations were made from these points and from three small vessels and the source vessel. Vocalising whales were tracked underwater with an array of hydrophones. These and other moored acoustic receivers recorded the sound field at several points throughout the area. Tags (DTAGs) were attached to whales with suction caps for periods of several hours. Observations and measurements during the experiments include the wide range of variables likely to affect whale response and sufficient acoustic measurements to characterise the sound field throughout the area. The remaining two experiments will be conducted further off shore off the west coast in 2013 and 2014

Migratory patterns and estimated population size of pygmy blue whales (Balaenoptera musculus brevicauda) traversing the Western Australian coast based on passive acoustics.

Passive acoustic data sets along the Western Australian coast have revealed annual southnorth migrations of pygmy blue whales. At the latitude of Exmouth (21o 30’ S) a sharp southerly travelling pulse of pygmy blue whales is experienced each year over October to late December, while a more protracted northerly pulse of returning animals is detected over the following April to August. It is believed the south bound pulse of animals passing Exmouth are steadily migrating. The passive acoustic detections of pygmy blue whales off Exmouth have been converted to instantaneous counts of the number of individual whales calling. By assuming a range of proportions of animals calling of from 8.5-20% of total pygmy blue whales in the area, the number of individual whales calling has been converted to estimates of the number of whales in the noise logger listening area, at 15 minute increments across the southerly migratory pulse. This curve was integrated across the migratory season. The listening range of the noise logger and the whale swim speed along a known route were used to give whale residency time in the noise logger listening area. The integrated curve of whale days was divided by the residency time to give an estimate of 662-1559 pygmy blue whales passing the noise logger site during the 2004 southerly migratory pulse down the Western Australian coast. We know pygmy blue whales reside along the east Australian coast and in the southern Indian Ocean, thus the population estimate for Western Australia is a portion of the larger Indian and western Pacific pygmy blue whale population

Southern Hemisphere breeding stock 'D' humpback whale population estimates from North West Cape, Western Australia

Estimates of the abundance of breeding group ‘D’ humpback whales (Megaptera novaeangliae) are key to managing what is thought to be one of the largest populations of the species. Five years (2000, 2001, 2006, 2007, and 2008) of aerial surveys carried out over an eight-year period at North West Cape (NWC, Western Australia) using line transect methodology allowed trends in whale numbers to be investigated, and provided a base for comparison with estimates made approximately 400km south at Shark Bay (SB, Western Australia). A total of 3,127 whale detections were made during 74 surveys of the 7,043km2 study area west of NWC. Pod abundance for each flight was computed using a Horvitz-Thompson like estimator and converted to an absolute measure of population size after corrections were made for estimated mean cluster size, unsurveyed time, swimming speed and animal availability. Resulting estimates from the migration model of best fit with the most credible assumptions were 7,276 (CI = 4,993-10,167) for 2000, 12,280 (CI = 6,830-49,434) for 2001, 18,692 (CI = 12,980-24,477) for 2006, 20,044 (CI = 13,815-31,646) for 2007, and 26,100 (CI = 20,152-33,272) for 2008. Based on these data, the trend model with the greatest r2 was exponential with an annual increase rate of 13% (CI=5.6%-18.1%). While this value is above the species’ maximum plausible growth rate of 11.8%, it is reasonably close to previous reports of between 10-12%. The coefficient of variation, however, was too large for a reliable trend estimate. Perception bias was also not accounted for in these calculations. Based on a crude appraisal which yielded an estimated p(0) of 0.783 (0from independent observer effort, CV=0.973), the 2008 humpback population size could then be as large as 33,333. In conclusion, the work here provides evidence of an increasing breeding group ‘D’ humpback whale population, however more surveys are necessary to confirm whether the population is indeed increasing at its maximum rat

Estimating cetacean carrying capacity based on spacing behaviour.

Conservation of large ocean wildlife requires an understanding of how they use space. In Western Australia, the humpback whale (Megaptera novaeangliae) population is growing at a minimum rate of 10% per year. An important consideration for conservation based management in space-limited environments, such as coastal resting areas, is the potential expansion in area use by humpback whales if the carrying capacity of existing areas is exceeded. Here we determined the theoretical carrying capacity of a known humpback resting area based on the spacing behaviour of pods, where a resting area is defined as a sheltered embayment along the coast. Two separate approaches were taken to estimate this distance. The first used the median nearest neighbour distance between pods in relatively dense areas, giving a spacing distance of 2.16 km (± 0.94). The second estimated the spacing distance as the radius at which 50% of the population included no other pods, and was calculated as 1.93 km (range: 1.62-2.50 km). Using these values, the maximum number of pods able to fit into the resting area was 698 and 872 pods, respectively. Given an average observed pod size of 1.7 whales, this equates to a carrying capacity estimate of between 1187 and 1482 whales at any given point in time. This study demonstrates that whale pods do maintain a distance from each other, which may determine the number of animals that can occupy aggregation areas where space is limited. This requirement for space has implications when considering boundaries for protected areas or competition for space with the fishing and resources sectors

Blue whale calling in the Rottnest trench, Western Australia, and low frequency sea noise

Through January-April 2000 research was carried out off the Rottnest trench to search for blue or pygmy blue whales. A consortium of researchers carried out aerial surveys, boat based studies and acoustical measures. Historical records led us to believe that a Western Australian population of pygmy blue whales (Balaenopteridae musculus brevicauda, sub species of the true blue whale, B. m. musculus) existed, while a preliminary boat survey in 1994 suggested that some of these animals aggregated in the Rottnest trench west of Perth. This was confirmed in the early 2000 observations, in 30 days boat based searching 17 pygmy blue whales were sighted. Five thousand acoustic records were made, almost all of which had blue/pygmy blue whale calling in, some having up to six animals calling at once. Although of a slightly different format, recorded call components were of a similar character to those described from other populations. Also common were impuslive 'clicking' calls which were shorter than the 12-23 s blue whale call components and of low to very low frequency (< 1 Hz to 20 Hz). The literature suggests these are produced by fin whales but none were sighted. The low frequency (< 100 Hz) sea noise spectra from a series of 90 s recordings made every 10 minutes for 33.5 days was dominated was dominated by blue whale calling

Pygmy Blue Whale Diving Behaviour Reflects Song Structure

Passive acoustic monitoring is increasingly employed to monitor whales, their population size, habitat usage, and behaviour. However, in the case of the eastern Indian Ocean pygmy blue whale (EIOPB whale), its applicability is limited by our lack of understanding of the behavioural context of sound production. This study explored the context of singing behaviour using a 7.6-day biotelemetry dataset from a single EIOPB whale moving north from 31.5° S to 28.5° S along the Western Australian coast and a simultaneously collected, but separate, acoustic recording. Diving behaviour was classified using an automated classification schema. Singing was identified in the depth, pitch, and fluking time series of the dive profile. The EIOPB whale sang profusely as it migrated, spending more time singing during the day (76.8%) than at night (64.9%), and most during twilight periods (83.3%). The EIOPB whale almost exclusively produced the three-unit (P3) song while milling. It sang the two-unit (P2) song in similar proportions to the P3 song while travelling, except at night when P3 was sung 2.7 times more than P2. A correlation between singing depth, migration duration, and water temperature provides a biological basis to explain depth preferences for sound production, which may contribute to the cause of intra- and inter-annual sound frequency trends

Genetic diversity and structure of blue whales (Balaenoptera musculus) in Australian feeding aggregations

The worldwide distribution of blue whales (Balaenoptera musculus) has not prevented this species from becoming endangered due to twentieth century whaling. In Australia there are two known feeding aggregations of blue whales, which most likely are the pygmy subspecies (B. m. brevicauda). It is unknown whether individuals from these feeding aggregations belong to one breeding stock, or multiple breeding stocks that either share or occupy separate feeding grounds. This was investigated using ten microsatellite loci and mitochondrial DNA control region sequences (N = 110). Both sets of markers revealed no significant genetic structure, suggesting that these whales are likely to belong to the same breeding stock.5 page(s