Western Australian Coast Research Articles

Abundance estimates of Southern Hemisphere Breeding Stock ‘D’ humpback whales from aerial and land-based surveys off Shark Bay, Western Australia, 2008

Single platform aerial line transect and land-based surveys of Southern Hemisphere Breeding Stock ‘D’ humpback whales Megaptera novaeangliaewere undertaken off Shark Bay, Western Australia to provide absolute abundance estimates of animals migrating northward along the westernAustralian coast. The aerial survey flew a total of 28 flights, of which 26 were completed successfully, from 24 June–19 August 2008. The landbased survey was undertaken from Cape Inscription, Dirk Hartog Island, Shark Bay, during the expected peak of the whales’ northward migration,from 8–20 July. During the first week of the land-based survey, some double count effort was undertaken to provide information on the numbersof pods missed from the land station. The assumed period of northward migration was 2 June–7 September. Estimated abundance of northwardmigrating whales during that time is 34,290 (95% CI: (27,340–53,350)), representing an annual rate of increase of 12.9% (CV = 0.20) since anestimate of 11,500 in 1999. This estimate is based on an estimate of relative abundance of surface-available whales of 10,840 (8,640–16,860), andan estimated g(0) of 0.32. There were considerable practical difficulties encountered during the land-based survey which reduced the effectivenessof the dual-survey approach for estimating g(0) for the aerial survey. Furthermore only about 15% of whales were estimated to be within the visualrange of the land-based station. Alternative approaches for estimating g(0) from these data are therefore also presented, resulting in considerablyhigher estimates of around 0.6–0.7, and yielding a conservative abundance estimate of 17,810 (14,210–27,720).

Importance of Resolving Mesoscale Eddies in the Model Simulation of Ningaloo Niño

AbstractSatellite observational data and a regional ocean model are used to understand the evolution of Ningaloo Niño (NN) anomalies near Western Australian coast. In observation and high‐resolution (~3 km) simulations, coastally trapped positive sea level anomalies (SLAs), originated largely from the Indonesian Throughflow, are transmitted westward by mesoscale eddies. Few eddies propagate long distances offshore due to dissipation, and as a result NN signatures are predominantly confined near the coast. In coarse‐resolution (~100 km) simulations that cannot resolve eddies, oceanic anomalies propagate swiftly as long Rossby waves with much weaker dissipation and more anomalies spread to the ocean interior. Eddy‐enhanced surface warming promotes surface latent heat release and mesoscale air‐sea interactions, which acts to damp NN surface warming. These processes are not resolved by coarse‐resolution models. This study highlights the importance of resolving mesoscale oceanic processes in the simulation and prediction of NN.

The Zeewijk Story and the Missing Second Wreck

The Dutch East India Company (VOC) ship Zeewijk was wrecked on Half Moon Reef in the Pelsaert (southern) Group of the Houtman Abrolhos islands off the Western Australian coast in 1727. The survivors were able to land on a nearby island, where they eventually built a rescue boat and finally reached their intended destination of Batavia (modern Jakarta) nine months later. At the time of the wreck, the survivors reported evidence of another shipwreck in the area. This paper describes these chronological events, the archaeological investigations and surveys of the site; and it attempts to analyse the veracity of the evidence of a second wreck.

Widespread seagrass meadows during the Early Miocene (Burdigalian) in southwestern Australia paralleled modern seagrass distributions

The Trealla Limestone, which forms a veneer of foraminiferal-rich limestone and covers over 4000 km2 of the tectonically stable Southern Carnarvon Platform, contains the oldest evidence for seagrass meadows known in Western Australia. It belongs to Lower Tf1 Letter Stage (based on larger benthic foraminifers) of the Burdigalian, within interval 19–16 Ma, and is the only Miocene unit on the platform. The Trealla Limestone here is coeval to the deeper water lower part of the much thicker Trealla Limestone in the Exmouth Sub-basin to the northwest. A seagrass-meadow depositional environment is indicated by most of the studied microfacies based on comparisons with modern sediment composition and foraminiferal assemblages found in innermost shelf seagrass banks between 23°S and 32°S on the present Western Australian coast. Some levels in the Trealla Limestone on the platform (e.g. with abundant miliolid foraminifers, and absence of coral debris) probably were deposited in and around dense seagrass meadows similar to those present today in the metahaline (40–55 ppt salinity) reaches of Shark Bay; whereas other levels (e.g. coral floatstone) were deposited under normal-marine conditions. Based on comparisons with modern carbonate sediment and biota in the region, the biogenic composition of the Trealla Limestone on the platform suggests winter minimum sea-surface temperatures within the range of 17–22 °C. The Nullabor Limestone in the Eucla Basin, at 10° further south on the southern Australian margin, is similar, at least in part, in composition and age to the Trealla Limestone on the Southern Carnarvon Platform. Both may have been deposited during a Burdigalian sea-level rise, and during part of the Miocene climate optimum recognized elsewhere. Sediment composition and foraminiferal assemblages (including epiphytic types) found in the Trealla and Nullabor limestones are similar to those in the modern seagrass banks of the region. This suggests that seagrasses similar to the extensive Posidonia and Amphibolus stands, which are dominant today between 25°S and 35°S along the Western Australian coast, were widespread during the Burdigalian.

Functional traits reveal the presence and nature of multiple processes in the assembly of marine fish communities.

Functional traits can be used to identify the importance of various community assembly mechanisms such as ecological drift, environmental filtering, and limiting similarity. These processes act in concert, not isolation, and different processes may act upon separate traits, potentially concealing the ecological signal of one or more of the mechanisms. Nine functional attributes of marine fish were used to identify changes in the importance of various mechanisms in the assembly of marine fish communities over a latitudinal gradient along the Western Australian coast. Complementary null modelling approaches were used to test the relative importance of assembly processes (ecological drift, environmental filtering, and limiting similarity) in structuring fish communities. Ecological drift was found to be a major driver of the structure of fish communities, and dispersal limitation was strongest in the tropical region, with homogenising dispersal strongest in the temperate region. Dispersion of functional traits identified environmental filtering acting on most traits incorporated in this study, in addition to limiting similarity acting on traits associated with acquisition of trophic resources. The coexistence of Western Australian marine fishes thus results from concurrent ecological drift, environmental filtering, and limiting similarity structuring the communities. The observed ecological drift may be the result of priority effects and/or context-dependent biotic interactions. Both niche complementarity and predator avoidance may be the drivers of the observed limiting similarity in the communities.

A Cenozoic Great Barrier Reef on Australia's North West shelf

Abstract The Great Barrier Reef of Australia is the largest modern coral reef system on Earth. However, a similar-sized barrier reef (~2000 km long) existed on Australia's north-western margin in the middle Miocene and to some extent, still exists today. Seismic profiles reveal that this reef system was first initiated in the late Paleogene (~34–28 Ma) and reached its zenith as a prograding barrier reef during the middle Miocene (16–15 Ma). This giant reef system backstepped in the late Miocene (~10 Ma), forming a series of isolated atolls and pinnacle reefs. These remaining reefs were gradually extinguished, leaving only a few surviving isolated atolls today (Rowley Shoals, Scott Reef, Seringapatam Reef and Ashmore Reef). The distribution of these extant reefs therefore outlines the former presence of the mid-Miocene Great Barrier Reef of the Australian North West Shelf. This middle Miocene shallow-water rimmed-reefal shelf grew contemporaneously on a deeper-water heterozoan ramp, producing an unusual mixed heterozoan/photozoan carbonate system for most of its length. The initiation of reef growth appears related to Australia's northward drift into lower latitudes, combined with warm mid-Miocene climatic optimum conditions. However, the sudden and simultaneous initiation of reef growth in the mid-Miocene across the North West Shelf was probably also related to changes in paleoceanography (increased aragonite saturation and/or nutrient-depletion) perhaps influenced by changing climatic conditions (increased aridity). From the late Miocene (~10 Ma) to Holocene, high rates of subsidence across the North West Shelf probably set the scene for ultimate demise of this giant barrier reef system and led to widespread backstepping with the development of a series of isolated atolls and pinnacle reefs. It is likely that other paleoceanographic and climatic events (like nutrient supply, carbonate saturation, eustasy etc) combined with continued high subsidence rates acted to gradually extinguish the reef system in a series of steps over a period of 10 million years. The onset (~1 Ma) of a strong Leeuwin Current (with the delivery of warm and nutrient depleted water from the north) and its effect on the Quaternary reefs of the Western Australian coast is a good example of a paleoceanographic process that would be difficult to recognize in an ancient setting. It is likely that similar paleoceanographic events have controlled the rich and complex history of reef growth and drowning since the mid-Miocene on the North West Shelf.

Ningaloo Niño/Niña and their regional climate impacts as recorded by corals along the coast of Western Australia

Ningaloo Niño/Niña is characterized by abnormal warming/cooling of sea surface temperature (SST) along the coast of Western Australia, leading to coastal marine ecosystem disruptions and abnormal climate conditions in the eastern Indian Ocean and Western Australia. Owing to short instrumental records, long-term Ningaloo Niño/Niña variability and its impacts on regional climate are less understood. In this study, coral δ18O records with bimonthly resolution from two sites along the Western Australian coast are used to investigate the relationship between coral δ18O and local SST. Significant correlations exist between coral δ18O and Ningaloo SST with 1-month lag, and thus the former is employed to represent Ningaloo Niño/Niña variability during 1854–1993. Coral δ18O reveals that the Ningaloo Niño/Niña features interdecadal variations, occurring more frequently in the periods of 1860–1890 and 1900–1970. Correspondingly, the impacts of Ningaloo Niño/Niña on the northwestern Australian (NWA) rainfall exhibited marked interdecadal variations in the 20th century. Significant correlations between Ningaloo Niño/Niña and NWA rainfall occurred from 1900 to 1970, a period when frequent Ningaloo Niño/Niña events were recorded by coral δ18O. An increase in the correlation with rainfall in the recent decades was revealed in the instrumental records. Therefore, our study indicates the potential of using tropical corals to study long-term Ningaloo Niño/Niña variability and their regional impacts.

Stable Isotope Analysis of Dermis and the Foraging Behavior of Whale Sharks at Ningaloo Reef, Western Australia

In order to examine the foraging behavior of whale sharks at Ningaloo Reef in Western Australia, stable isotope analysis of the dermis was used to estimate 13C and 15N values. These were compared to isotope values obtained from likely species of local prey. Ontogenetic and sex-related variations in the isotopic composition of dermis were also examined. The 13C values of zooplankton and nektonic taxa at Ningaloo ranged from -18.9‰ to -16.5‰ reflecting the different carbon sources entering the food web (from a pelagic to a more inshore and benthic productivity). The isotopic composition suggests that whale sharks had greater reliance on pelagic primary and secondary productivity over a period of ~3 years. Whale shark isospace matched some of the potential prey at Ningaloo Reef including krill, zooplankton and polychaetes. Consistency on 13C values indicated regional foraging ranges across the Ningaloo Reef area and the western Australian coast. More variability in 15N values showed, however, the different patterns of foraging among whale sharks. There was evidence of enrichment in 15N occurring with increasing size in male and female whale sharks, a pattern that could have been due to changes in growth rate and trophic level with age and/or an ontogenetic shift in feeding grounds. Our study brings new insights into the diet and feeding habits of an important whale shark population over large temporal and spatial scales in the eastern Indian Ocean. Such temporal and spatial information is essential for a better conservation management of this highly migratory and elusive species.

Decadal SST Variability in the Southeast Indian Ocean and Its Impact on Regional Climate

Abstract The southeast Indian Ocean (SEIO) exhibits decadal variability in sea surface temperature (SST) with amplitudes of ~0.2–0.3 K and covaries with the central Pacific (r = −0.63 with Niño-4 index for 1975–2010). In this study, the generation mechanisms of decadal SST variability are explored using an ocean general circulation model (OGCM), and its impact on atmosphere is evaluated using an atmospheric general circulation model (AGCM). OGCM experiments reveal that Pacific forcing through the Indonesian Throughflow explains <20% of the total SST variability, and the contribution of local wind stress is also small. These wind-forced anomalies mainly occur near the Western Australian coast. The majority of SST variability is attributed to surface heat fluxes. The reduced upward turbulent heat flux (QT; latent plus sensible heat flux), owing to decreased wind speed and anomalous warm, moist air advection, is essential for the growth of warm SST anomalies (SSTAs). The warming causes reduction of low cloud cover that increases surface shortwave radiation (SWR) and further promotes the warming. However, the resultant high SST, along with the increased wind speed in the offshore area, enhances the upward QT and begins to cool the ocean. Warm SSTAs co-occur with cyclonic low-level wind anomalies in the SEIO and enhanced rainfall over Indonesia and northwest Australia. AGCM experiments suggest that although the tropical Pacific SST has strong effects on the SEIO region through atmospheric teleconnection, the cyclonic winds and increased rainfall are mainly caused by the SEIO warming through local air–sea interactions.

Fin whale (Balaenoptera physalus) migration in Australian waters using passive acoustic monitoring

The fin whale is a globally endangered species and is listed as threatened in Australia, however no peer-reviewed studies are available to indicate the migratory movements of the species in Australian waters. This study uses passive acoustic monitoring as a tool to identify the migratory movements of fin whales in Australian waters. Sampling was conducted from eight locations around Australia between 2009 and 2017, providing a total of 37 annual migratory records. Taken together, our observations provide evidence of fin whale migration through Australian waters, with earliest arrival of the animals recorded on the Western Australian coast, at Cape Leeuwin in April. The whales travel through Cape Leeuwin, migrating northward along the Western Australian coast to the Perth Canyon (May to October), which likely acts as a way-station for feeding. Some whales continue migrating as far north as Dampier (19°S). On Australia’s east coast, at Tuncurry, fin whale seasonal presence each year occurred later, from June to late September/October. A total of only 8,024 fin whale pulses were recorded on the east coast, compared to 177,328 pulses recorded at the Perth Canyon. We suggest these differences, as well as the spatial separation between coasts, provide preliminary evidence that the fin whales present on the east and west coasts constitute separate sub-populations.

The eradication of ungulates (sheep and goats) from Dirk Hartog Island, Shark Bay World Heritage Area, Australia

The eradication of ungulates from offshore islands has now become achievable for island managers, with the size and complexity of an island no longer a major impediment to the desired outcome. Here, we report on a whole-of-island eradication campaign of ungulates (sheep Ovis aries and goats Capra hircus) from the semi-arid Dirk Hartog Island (63,300 ha) off the western Australian coast. The motive behind this campaign was to contribute towards the ecological restoration of this former grazing lease. From 2005, a concerted effort to remove ungulates began with regular destocking, and from 2010 a methodical aerial and ground shooting campaign was undertaken. Long-term commitments of funding and departmental support, staff with diverse skills, and an advisory network of professional people, have been critical components to this large-scale exercise. From 2005 to 2017 a total of 16,318 ungulates (5185 sheep and 11,133 goats) were removed from Dirk Hartog Island: 6839 by mustering, 2422 by ground shooting, 7040 by aerial shooting, and finally 17 by follow-up aerial monitoring and ground shooting. The island was declared free of ungulates in November 2017. To determine the success of the whole-of-island eradication campaign, multiple methods were adopted to locate remaining animals: use of ‘Judas’ goats, monitoring by motion-sensor cameras at water sources and across the island, and recording of tracks and fresh scats to locate any remaining animals. We estimated the likelihood that sheep and goats have been successfully eradicated from the island is 99.9% and 96.9%, respectively. The total cost (AUS$) of the aerial component of the eradication was $1,055,184, an average of $150/goat or $16/ha. The monitoring phase of the campaign (aerial detection and ground shoot) cost the least in terms of actual expenses (approximately $187,000) but the most is terms of cost per remaining goat (approximately $14,400). Ecosystem recovery following the eradication is already apparent with increased vegetation cover and reduced erosion. We conclude with some shared lessons that may assist similar large-scale eradication campaigns of islands. To date, Dirk Hartog Island is the largest island in the world where whole-of-island goat (and sheep) eradication has been achieved.

A seascape genetic analysis of a stress-tolerant coral species along the Western Australian coast

Genetic diversity and connectivity are key factors in determining a population’s resilience to future disturbance. This is especially relevant to corals, which are in global decline due to increasing frequency and strength of thermal anomalies and severe tropical cyclones. While many studies have investigated genetic diversity and population structure in corals, they focused on species being removed at the greatest rate from coral reefs, acroporids and pocilloporids, and it is unclear whether the patterns observed in these species reflects those found in more resilient species. Here, we use microsatellite markers and two Lagrangian models with differing resolutions, to investigate population structure in a stress-tolerant coral survivor Cyphastrea microphthalma, Family Merulinidae, along the north-western Australian coastline. We found evidence of four genetic clusters with some level of admixture among them. However, while there was evidence of population structure within the intensively sampled Pilbara region, the patterns of connectivity differed to those reported previously. WA populations of C. microphthalma were also characterised by lower levels of genetic diversity at higher latitudes. High- and moderate-resolution Lagrangian models did not significantly predict regional-scale genetic connectivity across the Pilbara and Ningaloo (500 km). Although the high-resolution model explained an order of magnitude more genetic variation, suggesting model resolution and resolving coastal processes are important. Over broad spatial scales (nearly 2000 km), all moderate-resolution model particle release durations significantly predicted the genetic differentiation, although over-water distance best-predicted the genetic distance across this spatial scale. This study improves the understanding of connectivity in this region by focusing on a stress-tolerant species incorporating a spatially more intensive sampling effort than previous coral studies. It also shows that further development of Lagrangian models is required, such as inclusion of multi-generational stepwise models and larval behaviour, to improve predictions of connectivity for this coral species in this region.

Altivasum Hedley, 1914 (Gastropoda: Turbinellidae) from South Western Australia

This paper seeks to correct the erroneous taxonomy associated with the current understanding of the Altivasum flindersi (Verco, 1914) complex based on type revision, morphological differences and geographic separation. Structurally, there are three distinct species that can be differentiated, Altivasum flindersi (Verco, 1914), A. typicum Hedley, 1916 and A. profundum sp. nov. Geographically, these species are not all sympatric, with A. typicum restricted to shallower waters, at depths around 20-180 m off the south Western Australian coast, whereas A. profundum is located at the edge of the South Western Australian continental shelf, and A. flindersi is found off the coast of the Great Australian Bight at similar depths to A. typicum. There is an overlap in distribution between A. typicum Hedley, 1916 and A. flindersi (Verco, 1914) on the western side of the Great Australian Bight where they are often associated with similar habitats.

Southbound migration corridor of pygmy blue whales off the northwest coast of Australia based on data from ocean bottom seismographs.

A line array of 14 ocean bottom seismographs was deployed on the Exmouth Plateau northwest of the North West Cape in Western Australia in December 2014-January 2015. Acoustic data collected with this array were used to evaluate the corridor of the southbound migration of pygmy blue whales of the eastern Indian Ocean population. It is found that pygmy blue whales tended to travel southward much further away from the Western Australian coast, at distances of up to 400 km from shore, than that expected from data on their northbound migration. This is an important observation providing additional information on the migration pattern of pygmy blue whales, which is crucial for assessing their population and migration by passive acoustic means.

Pygmy blue and Antarctic blue whale presence, distribution and population parameters in southern Australia based on passive acoustics

Passive acoustic recorders set around Australia since 2004 have been used to study blue whales. Calls from New Zealand pygmy blue whales occur predominantly eastward of Bass Strait (145.8° E), calls from Eastern Indian Ocean pygmy blue whales (EIO PB) west of Bass Strait, while Antarctic blue whale calls occur along the entire southern Australian coast. The only location all calls have been detected within a short space of time in the same season is Bass Strait, where inter-species mixing commonly occurs. The EIO PB shows three migratory stages: "southbound" from November to January during which whales travel down the Western Australian coast; "southern Australian" where animals spread across the Indian and Southern Oceans spanning longitudes from 74° to 146° E down to at least a latitude of 55° S searching for food and feeding; then a northern migration where they return north to Indonesian waters post April-August. Along the southern Australian coastline EIO PB whales are more often detected towards the east, favouring an area where late summer to autumn upwelling occurs mostly over ~ 134-145° E longitude. Receivers on the shelf break south of Portland (141.2° E) showed 10–181 times greater EIO PB whale calling when integrated over their three month season than at sites located around the Great Australian Bight to the west. Within a season the Portland site did not show consistency of EIO PB whale presence or number of calling individuals, but when the number of calling individuals was integrated across a season and correlated with an upwelling index of seasonally integrated seabed water temperature across seven seasons, the upwelling index predicted 83% of the seasonal variance in whale presence. The strength of this correlation will be reduced by population growth of whales. By correcting EIO PB whale call rates for a variety of population growth rate values, we found a 4.3% growth rate for the population proportion visiting the Portland area, gave the maximum regression, correlation coefficient of r2= 90%. Time averaged levels of squared pressure produced at the upper chorus frequency of the Antarctic blue whale z-call and received via deep sound channel propagation at Portland showed a 12.6% increase rate. This is indicative of population growth rate for Antarctic blue whales using waters south of Australia, although the value of using pressure squared in this fashion and the assumptions underlying the technique need to be explored.

Marine debris pathways across the southern Indian Ocean

The distribution of marine debris both with the open oceans and along coastlines is largely governed by surface currents and thereby dependent upon seasonal circulation patterns and annual variability inherent in the major current systems. The recovery of a satellite-tracked current drifter on a South African beach some 22 months after release off Western Australia was an indicator of the ocean-wide processes operating in the southern Indian Ocean gyre. Using this single drift trajectory in combination with data from other current drifters released along the Western Australian coast between 2008 and 2013, from earlier satellite-tracked drifters and a selection of historical drift bottle returns, drift patterns across the southern Indian Ocean between Western Australia and east Africa were analysed to quantify inter-continental debris transport rates via the South Equatorial Current (northern east-west pathway) and the South Indian Ocean Current (southern west-east pathway). The northern east-west trans-ocean pathway can be considered in three segments: the complex and highly variable Leeuwin Current eddy system in the east, which can retain drifting debris for up to a year, the comparatively uniform westward travel in the South Equatorial Current, and the eddying components in the western boundary current system off southern Africa. A simple Eddy Activity Index is derived here to clearly distinguish the Leeuwin Current eddy region from the South Equatorial Current. The southern route to Australia is simpler via the Agulhas Return Current and the South Indian Ocean Current.

Optimizing an oceanographic-larval model for assessment of the puerulus settlement of the western rock lobster, Panulirus cygnus, in Western Australia

Western rock lobster larvae have a 9–11 mo pelagic larval phase that makes them susceptible to the oceanographic environment, such as the poleward-flowing Leeuwin Current, surface winds, and wave-induced Stokes drift. An innovative oceanographic-larval modelling approach, which incorporated these physical drivers and complex larval behavior, was used to investigate the cause of the major reduction in postlarval (puerulus) settlement in the late 2000s. Individual-based biophysical larval models, taking into account the sensitivity to different wind effects on the surface water movement and different levels of puerulus swimming, were developed utilizing 19 yrs of meteorological and oceanographic data (1994–2012). Model optimization was achieved by assessing modelled and observed puerulus settlements along the Western Australian coast for 24 model simulations with different combinations of model parameters. A postmodel analysis then assessed the effect of the timing of larval release, abundance and spatial distribution of larval release, and duration of larval development. Model results revealed that a mismatch between the seasonal timing of spawning, larval development, and onshore current systems needed to return the larvae to the coast appears to be the primary cause of the low settlement in the late 2000s. Since the mid-2000s, there has been an earlier start of the spawning season due to warmer winter temperatures, which may have caused the ocean currents and eddies to diffuse the larvae in the open ocean before they can be transported back to the coast by onshore currents and weakened winter storms.

Evidence for a widely expanded humpback whale calving range along the Western Australian coast

AbstractThe recognized calving grounds of humpback whales (Megaptera novaeangliae) that breed along the Western Australian coast (Breeding Stock D) extend along the Kimberley coast between Camden Sound and Broome (15°–18°S). However, there are reports of neonates further south, suggesting that the calving areas may be poorly defined. During aerial photogrammetric research in 2013 and 2015, we sighted large numbers of humpback whale calves along North West Cape (21°47′–22°43′S). We estimated the minimum relative calf abundance to be 463–603 in 2013 and 557–725 in 2015. We categorized the calves as either neonate or post neonate according to their color and size. The majority of calves sighted in both years (85% in 2013; 94% in 2015) were neonates. Our observations indicate that a minimum of approximately 20% (17.1%–24.3%) of the expected number of calves of this population are born near, or south of, North West Cape. We thus demonstrate that the calving grounds for the Breeding Stock D population extend south from Camden Sound in the Kimberley (15°S) to at least North West Cape (22°43′S), 1,000 km southwest of the currently recognized calving area.

Movement, distribution and marine reserve use by an endangered migratory giant

AbstractAimUnderstanding the spatial and temporal variation in the distribution of migratory species is critical for management and conservation efforts. However, challenges in observing mobile marine species throughout their migratory pathways can impede the identification of critical habitat, linkages between these habitats and threat‐mitigation strategies. This study aimed to gain insight into the long‐term residency and movement patterns of the whale shark (Rhincodon typus) and to reveal important habitat in the context of R. typus usage of existing Marine Protected Areas (MPAs).LocationSouth‐eastern Indian Ocean.MethodsSatellite telemetry was used to remotely track the long‐term movements of 29 R. typus, and to quantify shark usage of the existing MPA network. From the tracking data and environmental predictors, nonlinear models were developed to predict suitable R. typus habitat throughout the south‐eastern Indian Ocean.ResultsThis study includes the first documented complete return migrations by R. typus to Ningaloo Marine Park, which was found to be an important area for R. typus all year‐round. We found that while existing MPAs along Australia's west coast do afford some protection to R. typus, telemetry‐based habitat models revealed large areas of suitable habitat not currently protected, particularly along the Western Australian coast, in the Timor Sea, and in Indonesian and international waters.Main conclusionsAnimal‐borne telemetric devices allowed the gathering of long‐term spatial information from the elusive and highly mobile R. typus, revealing the spatial scale of their migration in the south‐eastern Indian Ocean. Suitable habitat was predicted to occur inside conservation areas, but our findings indicate that the current MPA network may not sufficiently protect R. typus throughout the year. We suggest that telemetry‐based habitat models can be an important tool to inform conservation planning and spatial management efforts for migratory species.

High-Frequency Modulated Signals Recorded Off the Antarctic Peninsula Area: Are Killer Whales Emitting Them?

High-frequency modulated signals with a stereotyped down-swept contour were recorded in the northwestern Antarctic Peninsula using an autonomous recorder and a towed hydrophone array. Signals have a mean start frequency at 21.6 kHz, end frequency at 15.7 kHz, −10 dB bandwidth of 5.9 kHz, and duration of 65.2 ms. Bouts of signals were generally recorded with a median inter-signal interval of 2.1 s. HFM signals partially modulated in the non-ultrasonic range similar to the ones described in this paper have already been reported for killer whales in the North Pacific, Western South Atlantic and Western Australian coast. The HFM signals were recorded in the presence of other odontocete sounds such as whistles, echolocation clicks and burst-pulsed sounds. The similarities of these sounds with vocalizations described for killer whales in the Western Australian coast lead us to strongly believe that the described HFM signals were produced by Antarctic killer whales. This paper described for the first time HFM signals in Antarctica and discussed evidence suggesting that Antarctic type A killer whales are the most probable candidates to produce such signals. However, a visual confirmation is still needed and the function of the HFM signals remains unknown.