The Needle in the Haystack: Uncovering the First Whale Shark ( Rhincodon typus ) Aggregation in the Southwest Pacific

The Needle in the Haystack: Uncovering the First Whale Shark ( Rhincodon typus ) Aggregation in the Southwest Pacific | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Ecology and Evolution This is a preprint and has not been peer reviewed. Data may be preliminary. 4 April 2025 V1 Latest version Share on The Needle in the Haystack: Uncovering the First Whale Shark ( Rhincodon typus ) Aggregation in the Southwest Pacific Authors : Ingo Miller 0000-0002-9406-2012 [email protected] , Richard Fitzpatrick , Kátya Gisela Abrantes , Brad Norman , Simon Pierce , Mark Erdmann , Lisa Hoopes , … Show All … , Christine Dudgeon , Matthew Dunbabin , Alistair Dove , Robin Beaman , Samantha Reynolds , Christopher Rohner , Samuel Williams , David Paton , Sonny Lewis , and Adam Barnett Show Fewer Authors Info & Affiliations https://doi.org/10.22541/au.174375799.97408243/v1 893 views 219 downloads Contents Abstract Abstract Introduction Background Investigation: Data Layering Approach Physical Characteristics A Significant Piece of the Puzzle Methods Results Residency & Movement Patterns Discussion Acknowledgements Permits and Ethics Data Accessibility Funding Conflict of Interest Declaration Author Contributions Supplementary Material References Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Aggregations are key events, supporting critical ecological and biological functions in many species. For highly mobile and elusive species, aggregations often provide the only feasible opportunities for research. Whale sharks ( Rhincodon typus ) form at least 30 consistent seasonal aggregation sites globally, yet none have been documented in the southwest Pacific (SWP), despite sporadic sightings of solitary individuals and groups. This study aimed to identify and characterise the first whale shark aggregation on Australia’s east coast by predicting potential sites through a data layering approach and confirming their presence through targeted field expeditions. A combination of historical sightings data, expert and anecdotal knowledge, and scientific knowledge from other whale shark aggregation sites, led to the identification of Wreck Bay, situated at the far northern Great Barrier Reef, as potential aggregation habitat. An initial field expedition in 2019 confirmed the aggregation, and subsequent voyages gathered further demographic and movement data. A total of 59 individuals were identified, with a strong male bias (3.5:1) and all classified as immature sharks ranging from 3.5–8.0 m in estimated total length. Satellite tracking revealed a mean residence time of approximately three weeks (21.6 days ±10.1 SD; range: 7–43 days), with some individuals revisiting the aggregation in subsequent years. The core aggregation period occurs from late November to late December, with movements concentrated along the continental shelf before dispersing into the Coral Sea. Tracked sharks (n = 18) exhibited wide ranging movements, with a mean track duration of 144 days (range: 3–770 days) and a mean total track length of 1,463 km (range: 19–11,355 km). This study provides the first evidence of a whale shark aggregation in the SWP and highlights Wreck Bay as key habitat for this iconic and globally endangered species. Authors: Ingo B. Miller 1, 2, 3 , Richard Fitzpatrick 1 , Kátya Abrantes 1, 3 , Brad M. Norman 4, 5 , Simon J. Pierce 6, 7 , Mark V. Erdmann 8 , Lisa A. Hoopes 9 , Christine L. Dudgeon 1, 7 , Matthew D. Dunbabin 1, 10 , Alistair D. M. Dove 9, 11 , Robin J. Beaman 12 , Samantha D. Reynolds 4, 5 , Christoph A. Rohner 6 , Samuel M. Williams 13, 14 , David Paton 15 , Sonny Lewis 4 , Adam Barnett 1, 3 Affiliations: 1 Biopixel Oceans Foundation, Cairns, Qld, Australia 2 AIMS@JCU, College of Science & Engineering, James Cook University, Qld, Australia 3 Marine Data Technology Hub, James Cook University, Qld, Australia 4 ECOCEAN Inc., Coogee, WA, Australia 5 Harry Butler Institute, Murdoch University, Murdoch, WA, Australia 6 Marine Megafauna Foundation, West Palm Beach, FL, USA 7 School of Science, Technology and Engineering, University of the Sunshine Coast, Sunshine Coast, QLD, Australia 8 Conservation International Aotearoa, University of Auckland, Auckland, New Zealand 9 Georgia Aquarium, Atlanta, GA, USA 10 Robotics and Autonomous Systems, Institute for Future Environments, Queensland University of Technology, Brisbane, QLD, Australia 11 Museum of Science and History, Jacksonville, FL, USA 12 College of Science and Engineering, James Cook University, Cairns, Qld, Australia 13 Queensland Department of Agriculture and Fisheries, Brisbane, Qld, Australia 14 The School of Biological Sciences, The University of Queensland, St Lucia, Australia 15 Blue Planet Marine, Canberra, Kingston, ACT, Australia Corresponding author: Ingo B. Miller: [email protected] Abstract Aggregations are key events, supporting critical ecological and biological functions in many species. For highly mobile and elusive species, aggregations often provide the only feasible opportunities for research. Whale sharks ( Rhincodon typus ) form at least 30 consistent seasonal aggregation sites globally, yet none have been documented in the southwest Pacific (SWP), despite sporadic sightings of solitary individuals and groups. This study aimed to identify and characterise the first whale shark aggregation on Australia’s east coast by predicting potential sites through a data layering approach and confirming their presence through targeted field expeditions. A combination of historical sightings data, expert and anecdotal knowledge, and scientific knowledge from other whale shark aggregation sites, led to the identification of Wreck Bay, situated at the far northern Great Barrier Reef, as potential aggregation habitat. An initial field expedition in 2019 confirmed the aggregation, and subsequent voyages gathered further demographic and movement data. A total of 59 individuals were identified, with a strong male bias (3.5:1) and all classified as immature sharks ranging from 3.5–8.0 m in estimated total length. Satellite tracking revealed a mean residence time of approximately three weeks (21.6 days ±10.1 SD; range: 7–43 days), with some individuals revisiting the aggregation in subsequent years. The core aggregation period occurs from late November to late December, with movements concentrated along the continental shelf before dispersing into the Coral Sea. Tracked sharks (n = 18) exhibited wide ranging movements, with a mean track duration of 144 days (range: 3–770 days) and a mean total track length of 1,463 km (range: 19–11,355 km). This study provides the first evidence of a whale shark aggregation in the SWP and highlights Wreck Bay as key habitat for this iconic and globally endangered species. Keywords: Rhincodon typus, elasmobranch, constellation, conservation, Great Barrier Reef, IUCN, marine megafauna Introduction Aggregations are key ecological phenomena observed across a broad spectrum of species of all sizes, both in aquatic and terrestrial environments (Krause & Ruxton, 2002; Parrish & Edelstein-Keshet, 1999). These congregations, often of seasonal occurrence, may comprise from tens to millions of individuals, and may include single or multiple species (Parrish & Edelstein-Keshet, 1999). The locations where animals aggregate serve as essential habitats (Barnett et al., 2019; De Wysiecki et al., 2023), playing a crucial role in supporting key biological and ecological functions, including feeding, reproduction, and/or shelter (Morrell & James, 2008; Parrish & Edelstein-Keshet, 1999). Consequently, these habitats are fundamental to the survival and success of the species that depend on them. For instance, over one million wildebeest ( Connochaetes taurinus ) migrate across the Serengeti in East Africa in pursuit of high-quality vegetation that shifts seasonally (Morrison & Bolger, 2012; Subalusky et al., 2017). One of the largest known terrestrial aggregations occurs among straw-coloured fruit bats ( Eidolon helvum ), where up to 10 million individuals gather in Zambia’s Kasanka National Park to exploit seasonal food surges (Fahr et al., 2015). In the marine realm, aggregations often form near oceanographic features such as nutrient-rich upwelling zones sustaining high density primary production, leading to abundant zooplankton, which in turn attract larger predatory teleosts, sharks, and marine mammals (Botsford et al., 2003; Jacox & Edwards, 2011; Johnson et al., 2018; Kingsford & Wolanski, 2019). Seasonal events like the South African sardine run or Pacific salmon migration in the Gulf of Alaska exemplify how aggregations can drive predator-prey interactions (Furey et al., 2018; O’Donoghue et al., 2010). Marine aggregations can also serve crucial physiological and reproductive functions. Emperor penguins ( Aptenodytes forsteri ), for example, aggregate in large colonies to thermoregulate and enhance breeding success in the Antarctic winter (Ancel et al., 2015), while millions of Christmas Island red crabs ( Gecarcoidea natalis ) conduct synchronised mass migrations to coastal areas for reproduction (Adamczewska & Morris, 2001). Aggregations often present the only feasible opportunity to study certain taxa, particularly for highly mobile and elusive marine species, often due to the logistical challenges and costs involved. A prime example of such species is the whale shark ( Rhincodon typus ), the world’s largest extant fish, which is classified as Endangered and in decline globally (Pierce & Norman, 2016). There are currently approximately 30 known whale shark aggregations, also known as “constellations”, across their tropical and subtropical global distribution (Norman et al., 2017; Rohner et al., 2021b). Whale sharks often aggregate to feed on seasonally available dense patches of zooplankton – their primary food source (Rohner & Prebble, 2021). Research at these aggregation sites has been instrumental in advancing scientific understanding of the species, assessing population sizes, informing IUCN Red and Green List evaluations, and guiding conservation efforts (Pierce et al., 2021a; Pierce & Norman, 2016; Rowat & Brooks, 2012). The southwest Pacific (SWP) is a notable blind spot in global scientific data collection on whale shark ecology and conservation (cf. Fig. A1) (Pierce & Norman, 2016; Rohner et al., 2021b; Womersley et al., 2024). While whale sharks are sporadically sighted along the east coast of Australia and in the Coral Sea, encounters typically involve solitary individuals. Without spatial and temporal knowledge of an aggregation, finding whale sharks in this vast oceanic expanse is akin to finding a needle in a haystack. Given the sporadic sightings, the aim of this study was to determine whether a previously undocumented whale shark aggregation exists on the east coast of Australia and to assess the ecological role and significance of the area to the species, providing a foundation for future research in the region. For this, the study takes two approaches: first a data layering-approach was used to predict the most likely locations for whale shark aggregations to occur. Second, we conducted field expeditions to confirm the presence of an aggregation at the predicted area, and to characterise the aggregation using demographic information and satellite telemetry. Background Investigation: Data Layering Approach To search for potential whale shark aggregation areas along the expansive eastern Australian coastline with limited resources, we first collated information from a range of sources to narrow down the most promising search areas. These preliminary investigations provided the foundation for the subsequent field expeditions. Historical Sightings We first gathered historical sightings data from public databases that report marine species sightings. These included Sharkbook: Wildbook for Sharks (https://www.sharkbook.ai) and the Eye on the Reef sightings network (https://eotr.gbrmpa.gov.au/home). To complement these, we conducted social media mining (i.e., Instagram, YouTube, Facebook), and sought out anecdotal sightings reports from members of the public, including fishers and tourism operators. Files were screened for duplicates, retaining the records with the most detailed information. In cases where the number of animals was reported as a range, or when the numbers differed for the same encounter reported in multiple databases, the midpoint was selected as a conservative estimate. Sightings with no date or adequate location information were omitted. For instance, marlin fishermen frequently report encountering whale sharks during the marlin fishing season (October–November); however, only sightings with documented locations were included in the analysis. Additionally, we reviewed the scientific and grey literature to screen for information that might provide insights into historical sightings or ecological patterns associated with whale sharks in the region. A review of published literature revealed that the first scientific evidence of whale sharks on the east coast of Australia emerged in the 1960s, summarised in Wolfson (1986). A number of single whale sharks were recorded along the New South Wales coast between 1936 and 1965 (Whitley, 1965; Wolfson, 1986). Whitley (1965) also mentioned single sightings off Townsville in 1955 and 1956, and, more significantly, “a group of about 30 whale sharks” near Murray Island at the northern extent of the GBR “early in 1963”. In November 1983, a group of four whale sharks was also observed near Murray Island (Simmons & Marsh, 1986). Together, these observations provide first documented indication that whale sharks may aggregate on the east coast of Australia (Fig. 1-A: “MI”). In November 1985, aerial surveys conducted for dugongs ( Dugong dugong ) recorded nine whale sharks on the mid to outer shelf near latitude 12°S; however, all sightings involved solitary individuals (Marsh, 1990). Later, in October–November 1991, a “large number” of whale sharks was reported at Bougainville Reef in the Coral Sea off Cooktown (Fig. 1-A: “BV”), associated with an aggregations of yellowfin tuna ( Thunnus albacares ) and bigeye tuna ( T. obesus ) feeding on lanternfish spawn (Hampton & Gunn, 1998). Similarly, Wolanski and Hammer (1988) noted that whale sharks have been observed swimming and feeding on plankton slicks associated with upwelling in the centre of passages in the Ribbon Reefs in the northern GBR. While the timing of the latter observation is unclear, all other reports occurred in the months of October and November and were reported in association with other megafauna and/or abundance of plankton, suggesting that the northern GBR area is productive at this time of the year and potentially suitable for whale shark aggregations. With the implementation of public sightings reporting networks in the early 2000s, the number of whale shark sightings reported on the east coast of Australia has steadily increased. Between 2007 and 2018, 204 whale sharks were recorded from 136 encounter reports, with annual numbers reported rising after 2010 (Fig. A2-A). Lower number of sightings reported before 2011 likely reflects the early stages of these networks, as public awareness of the reporting tools was developing. For the most part, sightings were sporadic along the Queensland coast and mostly individual whale sharks were reported (Fig. 1, Fig. A2). While sharks were spotted all-year round except for May, nearly three-quarters (71%) of single individuals were spotted between October and January (Fig. A2). Only 10 of the encounter reports consisted of two or more whale sharks, however, those groups amounted to nearly 40% (n = 78) of all spotted sharks. Importantly, grouped whale sharks were exclusively recorded between September and January, with 90% of these sightings in November and December, and 73% in November alone (Fig. A2-C). While some sightings occurred in southern Queensland, including off Brisbane and Gladstone at the southernmost extent of the GBR, the majority were reported between the Townsville region in the central GBR and the far northern GBR around Wreck Bay (Fig. 1). The bulk of the reports were concentrated in the Townsville and Cairns regions, likely due to higher human population density and the Cairns region being the busiest reef tourism hub in Queensland (GBRMPA, 2025), resulting in more people engaging in water activities compared to more remote areas further north or south. Groups of whale sharks were observed in three key areas – Townsville in the central GBR, and Cairns and Wreck Bay in the northern GBR (Fig. 1). The only other site where more than one individual was recorded was off Gladstone, where three whale sharks were sighted in 2016, marking the southernmost record of grouped whale sharks. Between 2014 and 2017, five multi-individual encounters were recorded off Townville, with group sizes ranging from two to 20 individuals. One of these reports noted that a group of seven whale sharks was feeding on the surface alongside large schools of tuna. Cairns had two reports of three whale sharks occurring as a group, both in the month of November, in 2007 and in 2008. No other encounters of multiple whale sharks were reported around Cairns over the following 10 years. While whale shark encounters around Townsville and Cairns are spread out over a large area, the third hotspot had sightings of multiple whale sharks over the smaller area of Wreck Bay, located at the edge of the continental shelf in the remote far northern GBR (Fig. 1). In November 2011, the largest confirmed report of a group of whale sharks on the east coast of Australia was reported from the southern border of Wreck Bay, inside Mantis Reef (cf. Fig. 2), with a conservative estimate of 31 individuals (observed range of 12–50 animals from multiple reports of this encounter). It was also reported that the whale sharks were surface feeding on visibly dense patches of zooplankton. Another group of three sharks was observed in January 2018 also inside Mantis Reef. Within five days in October 2017, four individual whale sharks with different size estimates were observed in Wreck Bay, followed by another encounter two weeks later. It is likely that these encounters were of more than one individual, suggesting the presence of multiple sharks. However, to be conservative, they were considered as single individual sightings. Figure 1: Historical sightings of whale sharks ( Rhincodon typus ) along the East Coast of Australia. A) Sightings records are shown as circles, with size and colour differentiating the number of sighted whale sharks recorded in sightings databases between 2007 and 2018. Star-shaped locations depict notable evidence of whale shark clusters mentioned in scientific literature at Murray Island (MI) (Simmons & Marsh, 1986; Whitley, 1965; Wolfson, 1986) and Bougainville Reef (BV) (Hampton & Gunn, 1998). For the three apparent hotspots that emerged from this work (Wreck Bay, Cairns, Townsville), B) illustrates the monthly distribution of sightings in these regions. The Great Barrier Reef Marine Park boundary is shown as a dotted line. QLD = Queensland Physical Characteristics Bathymetric features are strongly associated with whale shark aggregations, in particular where shallow depths are in close proximity to steep slopes into deep water (mesopelagic zone) (Copping et al., 2018). Such characteristics create favourable conditions for upwelling, resulting in increased primary productivity and zooplankton abundance, which in turn attracts filter feeding species such as whale sharks (Heyman et al., 2001; Reynolds et al., 2024; Robinson et al., 2013; Rowat et al., 2006). For example, in the Azores archipelago, whale sharks occur more frequently in areas with steep bathymetric slopes near seamounts, coinciding with increased productivity and feeding opportunities (Afonso et al., 2014). To identify potentially suitable areas for whale shark aggregations along the GBR, we visually inspected regionally compiled, high resolution (30 m) bathymetric grids obtained from Project 3D-GBR (Beaman, 2017). This dataset integrates multibeam data – cleaned of anomalous noise within Teledyne Caris HIPS & SIPS software (Teledyne Technologies Inc., CA, USA) – and LiDAR bathymetry data to provide a seamless 3D depth model for the GBR and Coral Sea. Further details and data are available on the AusSeabed Marine Data Portal (https://portal.ga.gov.au/persona/marine). The bathymetry and oceanographic conditions in the northern areas, where groups of whale sharks have repeatedly been recorded, are distinctly different from those in the central and southern GBR. Unlike the central and southern regions, which are in general characterised by shallow waters with gradual slopes into the deep waters of the Coral Sea, the remote northern GBR (north of Cairns) features steep bathymetric slopes that descend into deep waters of the adjacent Coral Sea (cf. Fig. A3) (Hopley & Smithers, 2019). Such characteristics have been identified as key drivers of whale shark aggregations in other regions (Copping et al., 2018). Wreck Bay, where large groups of whale sharks have been repeatedly observed, has unique characteristics that distinguish it from other nearby shelf areas both north and south. Wreck Bay, consists of shallow, near-surface coral reefs that form a bay-like barrier, opening to the east (Fig. 2). This formation provides physical protection from wind, waves, and swell, facilitating calm conditions that likely retain and concentrate zooplankton, consequently ensuring a more consistent and predictable abundant food source for whale sharks. In contrast, upwelling-induced zooplankton in the more open shelf areas to the north and south are likely to be more rapidly dispersed, making food less abundant and predictable. Wreck Bay has a funnel-like shape, sloping from near-surface coral reefs into increasingly deep waters. Its entrance reaches a depth of 1,000 m, sloping further down to 2,000 m and eventually to 4,000 m in the Coral Sea basin (Fig. 2). The northern GBR shelf region experiences coastal upwelling during the monsoon season (November–February), bringing nutrient-rich deep water to the otherwise oligotrophic shallows (Berkelmans et al., 2010; Kingsford & Wolanski, 2019; Sun et al., 2024; Wolanski et al., 1988). This aligns with previous findings suggesting that the occurrence of whale sharks and baleen whales on the east coast between 12°S and 14°S latitude during November were consistent with upwelling events that occur on the upper continental shelf of the GBR at that time of the year, and the resulting enrichment with nutrients and plankton (Marsh, 1990; Wolanski & Hammer, 1988). However, upwelling is not limited to the northern continental shelf regions. For example, the identified whale shark hotspots off the coast off Townville also coincide spatially and temporarily with intrusive upwelling, which facilitates the exchange of water between the shelf and the Coral Sea through channels – a phenomenon commonly observed in the central GBR (Benthuysen et al., 2016). Figure 2: Westerly-looking 3D view of Wreck Bay, Great Barrier Reef, Australia. Bathymetry data courtesy of the Schmidt Ocean Institute and Australian Hydrographic Office. Vertical exaggeration x3. A Significant Piece of the Puzzle While evidence was increasingly pointing towards Wreck Bay as the most suitable area to explore for a whale shark aggregation, the next piece of the puzzle was delivered by opportunistically equipping a whale shark at Ribbon Reef No. 4, off Cooktown (Fig. 3) with a satellite transmitter (see below for satellite tagging procedures) in October 2018 – the first satellite tracked whale shark on the east coast of Australia and broader southwest Pacific. Post-tagging, this individual shark moved to Wreck Bay, where it remained for two weeks in November, further supporting the suspected location and timing for an aggregation to occur. Based on this suite of preliminary information, the Wreck Bay region in the far northern GBR during the months of November–January appeared to be the most likely site to find a whale shark aggregation. Figure 3: Satellite track of a whale shark ( Rhincodon typus ) opportunistically tagged at Ribbon Reef No. 4, off Cooktown, in October 2018. This individual moved to and resided in the Wreck Bay area for two weeks in November, confirming the projected location and timing that an aggregation is likely to occur. Satellite ‘World Imagery’ basemap provided by Esri, DigitalGlobe, GeoEye, and other contributors, accessed using the ‘basemaps’ R package (Schwalb-Willmann, 2024). Methods An initial field expedition to Wreck Bay was undertaken in November 2019 to confirm the existence of the suspected aggregation. Three further voyages were conducted 2021, 2023, and 2024 during the months of November/December to confirm that the site is an annual aggregation and to conduct further sampling. The expeditions included aerial surveys to find whale sharks, and satellite tagging and photo ID to track shark movements and to characterise the demography of the aggregation (Fig. A1). All data preparation, statistical analyses, modelling, and visualisations were performed using RStudio (Posit team, 2024), based on the statistical computing language R (Version 4.3.2, R Core Team, 2024). A significance value α of 5% was used for statistical tests. Statistical values are presented as mean and standard deviations (SD), unless otherwise stated. In case of skewed data, median values were given with the interquartile range (IQR) representing the variation in the data. Maps were created using the ‘ggplot2’ (Wickham & Sievert, 2016), ‘basemaps’ (Schwalb-Willmann, 2024), ‘ggspatial’ (Dunnington, 2023), and ‘sf’ (Pebesma & Bivand, 2023) packages. Aerial surveys While the expedition vessel was at Wreck Bay, a single engine high-wing aircraft (Cessna types 172, 182, and 210) with either one or two designated spotters was used to locate whale sharks by flying line-transects or circular search patterns throughout the Wreck Bay area during daylight hours. Position and time of sighting was recorded for all sighted whale sharks. Once a shark was located, the plane circled the individual and communicated its location and details to the expedition vessel. Tagging Procedures and Demographic Data Collection With guidance of the spotter plane, a drone (DJI Mavic Pro Cine) was manoeuvred to and hovered above the whale shark to provide a visual reference and direct the tender with the tagging team to the shark’s location. Continuous communication between the spotter plane and the drone operator was maintained to ensure safe separation between the tender and the whale shark. Individual whale sharks were identified by photographing their unique spot patterns behind the gills and above the pectoral fins and submitted to the Sharkbook: Wildbook for Sharks library (https://www.sharkbook.ai/). Each shark was assigned a unique ID (Table A1) and checked for matches in the database to identify potential connectivity with other sites (Arzoumanian et al., 2005; Norman et al., 2017). The size (total length TL in meters) was approximated using objects of known dimensions as reference points, e.g., researcher in the water, or boat (Norman & Stevens, 2007; Reynolds et al., 2024). Sex was determined visually by inspecting the pelvic fins for the presence of claspers (Norman & Stevens, 2007; Pierce et al., 2021b). Long and thick claspers that extend past the pelvic fins indicate calcification and thus maturity (Norman & Stevens, 2007; Rohner et al., 2015). Female maturity was assigned based on size, assuming maturity at around 9–10 m (Norman & Stevens, 2007; Pierce et al., 2021b). To compare differences in total length between males and females, a non-parametric Wilcoxon rank-sum test was performed using the ‘rstatix’ package (Kassambara, 2023), as the size data was not normally distributed (assessed using a Shapiro-Wilk test). Sharks were equipped with satellite-linked platform transmitter terminal (PTT) tags (Table A2) (Wildlife Computers, Inc., Redmond, WA, USA) – either with smart position and temperature (SPOT), or data archiving and satellite transmitting (SPLASH) tags – and tracked using the Argos-CLS satellite network (https://www.argos-system.org/). SPOT tags provide near-live tracking of horizontal geolocation data, while SPLASH tags also record depth time series data. SPOT (n = 15; models: SPOT-196, 257), and SPLASH tags (n = 2; model: SPLASH10-346) were attached to the first dorsal fin using custom made spring clamps, equipped with a set of spikes that grip and retain the tag on the fin (Gleiss et al., 2009; Norman et al., 2016). Titanium anchors were used for two tethered SPOT tags (SPOT-253) that were deployed opportunistically off Cooktown in 2018 (preliminary tagged shark, Fig. 3) and Cairns in November 2023 (Fig. 7). A handheld pole spear with a custom-made tip applicator was used to insert the titanium dart anchor intradermal (Hammerschlag et al., 2011) above the first prominent longitudinal ridge, approximately centred below the shark’s dorsal fin. The latter two individuals were not sexed, and no photo IDs were taken. Movement Data Analysis To analyse movement patterns and residency in the Wreck Bay aggregation, transmitted geolocation data from a total of 19 tagged whale sharks were included – 17 tagged during three dedicated field expeditions to Wreck Bay (2019, 2021, and 2023), and the two opportunistically tagged off Cooktown and Cairns in 2018 and 2023 (see Fig. 7 for locations). One SPOT tag (PTT 178950) failed to transmit data and was excluded, resulting in 18 shark tracks considered for further analyses. All tracks were processed using the ‘aniMotum’ R package (Jonsen et al., 2023). A correlated random walk state space model (SSM), which incorporates Argos Kalman filtered error ellipses, was fitted to all tracks, applying a speed filter of 1.15 m s –1 to remove implausible locations (Cade et al., 2020; Guzman et al., 2022). To determine residency of whale sharks within the Wreck Bay aggregation, each SSM track was clustered into behavioural segments using the ‘segclust2d’ package (Patin et al., 2020). The behavioural states were determined based on longitudinal and latitudinal displacement or based on speed and turning angle (Patin et al., 2020). Considered for residency analysis were those parts of the tracks, that indicated area restricted search behaviour. Detailed information on the segmentation process is provided in Table A3. Home range analysis was conducted to determine hotspot areas within the vicinity of the aggregation habitat, as described previously in Abrantes et al. (2024). Briefly, resident phases of the tracks were used to calculate autocorrelated kernel density estimates (AKDE) for each whale shark using the ‘ctmm’ package (Calabrese et al., 2016; Fleming et al., 2017). Twelve sharks had suitable tracks for home range estimation, including two multi-year tracks (PTTs 178954, 252324). For the latter sharks, AKDE’s were computed for each year they visited Wreck Bay. This resulted in a total of 14 track sections considered for home range estimation. The resulting individual AKDEs were used to estimate a population home range (i.e., PKDE). The 95%, 50% and 25% PKDE’s were extracted to visualise home range, core use areas, and high intensity core areas, respectively, including their 95% confidence intervals. Results Aerial Surveys Aerial surveys were conducted on five consecutive days in 2019 (Nov 15–19), 2021 (Dec 05–09), 2023 (Nov 29–Dec 03), and 2024 (Nov 28–Dec 02). Active spotting time was 3.5–4.0 hours per day and ranged between 09:00 h and 16:00 h. The number of whale sharks spotted during aerial surveys increased over the years, with 13 and 25 whale sharks recorded in 2019 and 2021, and 67 and 53 in 2023 and 2024, respectively. In total, 158 sharks were sighted over the course of the four expeditions. However, it is likely that some of these sightings were of the same individuals. Demography A total of 59 individual whale sharks were recorded in-water during the four expeditions to Wreck Bay. (Table A2). The majority of these sharks were males, with an overall male to female sex ratio of 3.5:1 (males: n = 45, 76%; females: n = 13, 22%), while the sex of one individual was not determined (Fig. 4A). Sex ratios varied over the years as the number of sharks identified increased (Fig. 4B). Of the four sharks identified in 2019, three were males, while the sex ratio of the 10 photo ID’d sharks in 2021 was balanced. The sex ratios in 2023 and 2024 were 3.5:1 (males: n = 14, 77.8%; females: n = 4, 22.2%) and 5.8:1 (males: n = 23, 82.1%; females: n = 5, 17.9%), respectively. Estimated total length ranged from 3.5 to 8.0 m (Fig. 4C). All sharks were immature, with four males classified as subadults based on clasper elongation without full calcification. Males were significantly larger ( W = 184.5, p = 0.042, n = 48), with an average size of 6.2 ±1.1 m (range: 4.0–8.0 m) compared to 5.5 ±1.0 m (range: 3.5–6.5 m) for females. Photo ID confirmed that one shark that was documented in 2023 (GBR-052), revisited Wreck Bay in 2024. None of the whale sharks had been identified elsewhere within the global Sharkbook database as of March 2025. Figure 4: Demographics of the Wreck Bay whale shark ( Rhincodon typus ) aggregation. Overall sex ratios of the 59 individuals recorded by Photo ID are shown in A), while B) illustrates the proportion of whale sharks per year, and the sex ratios per expedition. Size distributions of males (n = 45) and females (n = 13) are shown in C), with violin plots illustrating the density distribution of estimated total length. Boxes in the box-and-whisker plots depict the interquartile range (IQR, first and third quartile, Q1, Q3) and whiskers extend to 1.5x IQR from Q1 and Q3. The thick horizontal line within the box represents the median, while the star represents the mean. Raw data as shown as hollow circles. A Wilcoxon rank-sum test confirmed significant differences between the sexes ( W = 184.5, p = 0.042, n = 48); indicated by an asterisk above the plots. M = male, F = female, U = undetermined. Residency & Movement Patterns Twelve sharks (two females, eight males, and two with undetermined sex) had suitable movement patterns (in terms of tracking duration and number of transmitted geolocations) to allow for a distinct separation of movement behaviours, including departure from the Wreck Bay aggregation area (Table A3). The mean residence time in the general vicinity of the Wreck Bay area was approximately three weeks (21.6 ±10.1 days; range: 7–43 days), during which time an average of 43.1 ±35.5 geolocations (range: 7–145) were transmitted. The residence time is likely underestimated as it remains unclear how long the individuals had already been present in Wreck Bay before tagging. However, data from four sharks that were either tagged before reaching the aggregation area (n = 2) or tracked over multiple years after being tagged in Wreck Bay (n = 2) provide more accurate residency times. Based on track segmentation analysis of the two sharks tagged offshore from Cooktown and Cairns, one individual (PTT 172899, sex unknown, 5.0 m TL) remained in the Wreck Bay aggregation area for 14 days, while the other (PTT 172900, sex unknown, 5.1 m TL) stayed for about one month (34 days). For the two sharks tagged in Wreck Bay, a female (PTT 178954, 6.0 m TL) revisited the aggregation for two subsequent years, spending 11 days in the area during its first return in 2022, and 40 days in the second return in 2023. A male shark (PTT 252324, 7.0 m TL) tagged in 2023 spent approximately one month (30 days) in the aggregation area when it returned in the following year in 2024. Together, these four tracks suggest a general mean residence time of approximately three weeks (24.3 ±10.9 days), similar to the estimated residence time from all 12 sharks. Acknowledging the relatively small sample size, the data collected so far suggest that the core aggregation period at Wreck Bay occurs between late November and late December, with the earliest arrivals at the end of October and the latest departures in mid-January (Fig. 5). Potential area-restricted search behaviour (based on track segmentation analysis) predominantly occurred on the continental shelf area of the outer reefs, within approximately one degree latitude north and south of Wreck Bay, covering a latitudinal span of approximately 200 km. Figure 5: Whale shark ( Rhincodon typus ) residency based on the presence (large blue dots) and absence (black dots) in the vicinity of the Wreck Bay aggregation site. The orange rectangle represents residency in Wreck Bay based on the earliest and arrival and latest departure, while the red rectangle shows residency based on the median arrival and departure dates. The red dotted vertical line represents the earliest tag deployment (24 th of October). Numbers in parentheses after whale PTTs indicate the different aggregation seasons for multi-year tracks. Home range analysis of the overall tracked population suggests a home range area (95% PKDE) of 5,336 km 2 (17.9–24,411.1 km 2 95% CI), stretching over 140 km from the southern end of Saunder Reef to north of Bligh Reef (Fig. 6, Table A4). The core use (50% PKDE) extends over 57 km from the northern end of Wreck Bay to Sandy Reef in the south and covers an area of 815.5 km 2 (2.7–3,730.9 km 2 95% CI). The 25% PKDE area centred around Henry Reef, covering an area of 238 km 2 (0.8–1,090.0 km 2 95% CI). Figure 6: Population home range of aggregating whale sharks ( Rhincodon typus ) in the Wreck Bay area. Autocorrelated kernel density estimators (AKDE) were modelled for each shark’s area-restricted search behavioural segment of the tracks, and subsequently the populations’ KDE (PKDE) was estimated. The 95% (turquoise), 50% (magenta) and 25% (yellow) PKDE’s reflect the populations home range, core use areas, and high intensity core areas while aggregating in Wreck Bay, respectively. Dashed lines represent the upper 95% confidence intervals for each PKDE. Annotations in white depict the locations and names of coral reefs. Satellite ‘World Imagery’ basemap provided by Esri, DigitalGlobe, GeoEye, and other contributors, accessed using the ‘basemaps’ R package (Schwalb-Willmann, 2024). Upon departing from Wreck Bay, whale sharks dispersed into the Coral Sea and beyond. This pattern was most apparent between January and May, when geolocations were spread across a broad spatial range in both latitude and longitude (Fig. 7). Overall, the movements of tracked sharks spanned over 13˚ longitude (143˚E to 156˚E) and 12˚ latitude (18.6˚S to 6.2˚S). Distance travelled ranged from 19 km to 11,355 km track length per individual, with a median distance of 1,463 km (2,312 km IQR) (Table A1). Tag retention varied from 3–770 days, with an average of 144 ±209.63 days at liberty (DAL, Table A1). Of the three female tagged sharks, one tag failed to transmit data (PTT 178950). The other two females exhibited considerably longer tracks compared to males (n = 13) and sharks with unknown sex (n = 3). One female (PTT 178957, 6.0 m TL) transmitted for 526 days and the other (PTT 178954, 6.0 m TL) transmitted for 770 days. Male shark track durations ranged from 3–397 days with an average of 78.5 ±106 DAL, similarly to the sharks with unidentified sex, which averaged to 94.7 ±77.1 and ranged from 6–146 days. Interestingly, both females visited the Gulf of Papua, while no male sharks moved to that area. Figure 7: Spatiotemporal distribution of whale sharks ( Rhincodon typus ) (n = 18), satellite-tracked between October 2018 and December 2024. Map shows the transmitted geolocations by month and paths of individual sharks connected by white lines, with density plots indicating monthly latitudinal and longitudinal distribution of geolocations and values indicating the number of individual sharks per month. Crossed circles indicate tagging locations: Wreck Bay (“WB”), Ribbon Reef No. 4 (“R4”) off Cooktown, and Linden Bank (“LB”) off Cairns. ‘Ocean Basemap’ data product provided by Esri, GEBCO, NOAA, and other contributors. Discussion Here, we describe the first whale shark aggregation site documented on the east coast of Australia and the broader southwest Pacific region. Our investigative approach, layering multiple sources of information including insights from local experts and citizens’ observations alongside knowledge from research at known whale shark aggregations, was paramount to identify and confirm the location of an aggregation site in this region. Through four targeted field expeditions, we can now confidently confirm a seasonal whale shark aggregation at Wreck Bay, situated at the far northern Great Barrier Reef. To date, data suggests that the aggregation is dominated by juvenile males (75%, 4–8 m TL), which aligns with most known whale shark aggregations globally, where the percentage of males typically ranges from 62–97% and size distributions fall between 3–9 m (Araujo et al., 2022; Norman et al., 2017; Pierce et al., 2021b). Sex ratios at whale shark hotspots closest to Wreck Bay are similar, with ∼80% males at Ningaloo Reef (Western Australia), and ∼65% males in Indonesia (Araujo et al., 2022; Norman et al., 2017). Notable exceptions from the predominant male bias include aggregations in Shib Habil in the Red Sea, Saudi Arabia (Berumen et al., 2014; Cochran et al., 2016), and St. Helena in the Atlantic Ocean, where sex ratios are more balanced, with the latter dominated by mature sharks and with evidence of mating (Perry et al., 2020). Darwin Island, in the Galápagos, remains the only documented hotspot with a predominance of adult females (Hearn et al., 2016; Hearn et al., 2021). Given that demographic data are currently available for only 59 sharks in Far North Queensland, and that sex ratios varied across years, further data collection is required to comprehensively characterise the demography of the Wreck Bay whale shark aggregation. The mean residency period of three weeks in Wreck Bay is consistent with other aggregations, where residencies typically range from 19 days at St. Helena (Perry et al., 2020) to around one month at Ningaloo Reef (Holmberg et al., 2009) and Holbox/Isla Mujeres at the Caribbean coast of Mexico (Hueter et al., 2013), and two months in Baja California (Ramírez-Macías et al., 2012). However, the number of tagged sharks with a full year of data or more, needed to confirm site fidelity over multiple years, remains limited. In the present study, three individuals, two of which were females, transmitted data for more than one year, providing some insight into potential multi-year residency patterns and site fidelity. Two of these individuals revisited Wreck Bay in subsequent years, while the third (PTT 178957), a female tagged in 2021, exhibited sporadic and inconsistent data transmission with gaps of several months, with only 84 recorded locations over 500 days. Its last known position, recoded in May 2023, was in the Coral Sea off the northern Ribbon Reefs, about 100 NM south of Wreck Bay. While transience is a common trait in whale sharks across global aggregations (Pierce et al., 2021b), the single resighted shark in Wreck Bay is considerably lower than the 36% resightings on average reported at other aggregations (Norman et al., 2017). In Wreck Bay, logistical constraints due to the area’s remoteness limited sampling effort to only five days per season in four years since 2019. In contrast, at Ningaloo Reef, where 40% of identified animals were sighted over two or more calendar years, fieldwork has been ongoing for decades and occurs throughout the entire aggregation season (March–July), facilitated by research teams and citizen science initiatives (Meekan et al., 2006; Norman et al., 2016, 2017). Since 1986, over 2,300 individuals have been recorded in the Sharkbook database for Ningaloo Reef. Similarly, in the Philippines, where the resighting rate is 35%, whale sharks are observed year-round (Araujo et al., 2022), with over 800 individuals added to Sharkbook since 1998. Given our restricted sampling effort, it is possible that some previously identified individuals were in the area but remained undetected in subsequent years. Lack of resightings could also be influenced by the aggregation being distributed across a broad area, as indicated by home range analysis, and/or sharks spending limited time at the surface during the day. Daytime surface feeding was observed occasionally, and several individuals were also seen ram-feeding on dense zooplankton patches at night (from sunset to late into the night). Whale sharks show high plasticity of feeding behaviours, depending on the local food availability, ranging from passive, active, and stationary feeding (Rohner & Prebble, 2021) on the surface and in the water column at depth (Rohner et al., 2013), and benthic foraging (D’Antonio et al., 2024; Whitehead & Gayford, 2023). Most commonly observed at coastal aggregations is active surface feeding during the day (Motta et al., 2010; Rohner & Prebble, 2021), although observation bias may play a role in this (Rohner & Prebble, 2021). Nocturnal surface feeding on high-density plankton patches, as observed on multiple occasions in Wreck Bay, has, to our knowledge, previously only been regularly documented (under natural conditions) at Ningaloo Reef, where similar surface ram-feeding behaviour was reported to occur during sunset (Gleiss et al., 2013; Taylor, 2007). While further investigation is needed to quantify feeding patterns, these observations suggest that nocturnal foraging may be the predominant feeding behaviour in Wreck Bay. Whale sharks are not the only marine megafauna that utilise Wreck Bay during summer months, with black marlin ( Istiompax indica ) known to routinely migrate north from the Ribbon Reef group of Cairns, up to Wreck Bay during this period (Domeier & Speare, 2012; Williams et al., 2017). The spatiotemporal overlap of black marlin and whale sharks is not restricted to the Wreck Bay location, with these species co-occurring in other parts of the world including Ningaloo Reef in Western Australia, and Bazaruto Island in Mozambique (Pepperell et al., 2011; Rohner et al., 2014, 2021b; Wilson et al., 2001). Given that these species are among the most highly mobile on the planet it suggests that the biophysical attributes of these sites offer an important ecological niche that can support the needs of migratory species that forage at different ends of the food web (Domeier & Speare, 2012; Williams et al., 2017). During our field surveys, we also observed manta rays ( Mubula alfredi and M. birostris ) and Omura’s whales ( Balaenoptera omurai ) within Wreck Bay. Further work to understand whether the timing and occurrence of black marlin, and other co-occurring megafauna species, are associated with specific physical factors would help to identify other whale shark aggregations as well as the ecological value of these sites. Extensive whale shark movements have rarely been recorded, likely due to short satellite tag deployments and tag shedding (Hearn et al., 2021). In the current study, a female whale shark travelled at least 11,355 km over a period of over two years (770 d), representing one of the longest tag deployments and distances moved. Despite the long track distances indicating wide dispersal capabilities, most of the tracked whale sharks in this study remained within the Coral Sea region, except two individuals that moved into the Solomon Sea. Notable transoceanic movements include a 7.1 m whale shark of unknown sex that travelled nearly 13,000 km from the Sea of Cortez into the northwestern Pacific over a period of three years (Eckert & Stewart, 2001) and a 7 m female that travelled >20,000 km from Panama to the Mariana Trench in 841 days (Guzman et al., 2018). However, the accuracy of these tracks has been questioned, due to the lack of depth data and inconsistencies in location fixes (Hearn et al., 2021). The longest verified movement to date was recorded from an 8 m female fitted with a fin-mounted SPOT tag, travelling >40,000 km over four years, mostly within the Gulf of Mexico (Daye et al., 2024). In conclusion, we discovered the first whale shark aggregation on the east coast of Australia, which occurs annually at Wreck Bay in the remote northern Great Barrier Reef during the months of November and December. This is a first step to filling a significant gap in whale shark knowledge in the southwest Pacific. Unlike most whale shark studies, which typically commence at established aggregation sites, our research took the opposite approach – we set out to investigate whale sharks on Australia’s east coast without knowing where to start. This ‘needle in the haystack’ challenge required an innovative investigative strategy, combining local and expert knowledge, citizen science, and an understanding of what is driving whale shark movements and aggregations in other areas to pinpoint a previously unknown aggregation. This approach demonstrates how aggregations can be identified in data-poor regions and could be applied to other species or locations where critical habitats remain undocumented. While public databases have proven to be valuable resources, unfortunately we found that many whale shark encounters remain unreported. The identification of this critical habitat has important implications for the Great Barrier Reef Marine Park and Coral Sea Marine Park. Currently, whale sharks are not a priority for management in this region, however the data presented here highlights its importance for the species and emphasises the need to assess potential threats to whale sharks in their newly identified essential habitat. Nevertheless, beyond the GBR, our findings will contribute valuable data for future conservation assessments for this Endangered species (Pierce & Norman, 2016). Importantly, our findings indicate that Wreck Bay may not be the only aggregation site along the east coast of Australia. Sightings data highlighted other locations where groups of whale sharks have been repeatedly observed (i.e., off Townsville, Cairns), suggesting the possibility of additional, yet undocumented, aggregations. Furthermore, our tracking data reveal additional areas of interest where no prior sightings have been reported, such as the Gulf of Papua, underscoring the potential for undiscovered aggregation sites across the broader SWP region. Building species distribution models to identify potential suitable and essential to target further sites and expand research efforts, would be valuable steps toward improving our understanding of whale shark distribution, ecology, and aggregation dynamics in the southwest Pacific region. Acknowledgements This research has made use of data and software tools provided by Wildbook for Sharks , an online photo library operated by the non-profit scientific organization Conservation X Labs , the Eye on the Reef sightings network, and additional sightings data provided by Jessica Funnell. Multibeam bathymetry data courtesy of the Schmidt Ocean Institute’s RV Falkor expedition FK20030 ‘Northern Depths of the Great Barrier Reef’. Multibeam data collected under permit G20/43838.1. Shallow lidar bathymetry data courtesy of the Australian Hydrographic Office provided under licence for Project 3D-GBR. We thank Dan McCarthy and his crew at Big Fish Downunder for assisting with the tagging of whale sharks in the Cairns/Cooktown areas and providing vital insights into whale shark occurrence. Special thanks to the crew of Blue Planet Marine RV Infamis. We also thank Gesa Mueller and Cameron Perry for fieldwork assistance, as well as the spotter plane crews, particularly Hannah Robertson and Jasmin Behnke. SJP and CAR thank Waterlust, Aqua-Firma, and the Shark Foundation for support. Author IBM acknowledges support through an Australian Government Research Training Program Scholarship awarded by James Cook University and AIMS@JCU. Permits and Ethics Research was conducted under permits G18/39348.1, G21/144109.1 and G22/46908.1. All work conducted was approved by James Cook University Animals Ethics Committee (A2864). firstpage\fancyhf \lhead \chead \rhead \cfoot فروردین ماه ۱۴۰۴ Data Accessibility Sightings data as well as tracking data used for analysis are available on the Zenodo data repository: https://doi.org/10.5281/zenodo.15048664. Near-live tracks can be viewed at https://biotracker.tv/. Photo IDs were uploaded to Sharkbook: WIldbook for whale sharks : https://www.sharkbook.ai/, and links provided in Table A1. firstpage\fancyhf \lhead \chead \rhead \cfoot فروردین ماه ۱۴۰۴ Funding We acknowledge funding support by the Queensland Government’s Threatened Species Research (round 1) grant (TSR069), the Sapphire Project, Blancpain Ocean Commitment, Georgia Aquarium, Sea World Foundation (SWR/9/2023), Conservation International, MAC3 Impact Philanthropies, the Slattery Family Trust, and 4planet. firstpage\fancyhf \lhead \chead \rhead \cfoot فروردین ماه ۱۴۰۴ Conflict of Interest Declaration Authors declare no conflict of interest Author Contributions Ingo B. Miller : Conceptualization (Equal), Data curation (Lead), Formal analysis (Lead), Investigation (Equal), Methodology (Lead), Project administration (Equal), Visualization (Lead), Writing – original draft (Lead), Writing – review & editing (Lead) Richard Fitzpatrick : Conceptualization (Equal), Funding acquisition (Equal), Project administration (Equal), Resources (Equal), Writing – review & editing (Equal) Kátya G. Abrantes : Conceptualization (Equal), Funding acquisition (Equal), Project administration (Equal), Writing – review & editing (Equal) Brad Norman : Conceptualization (Equal), Investigation (Equal), Writing – review & editing (Equal) Simon J. Pierce : Conceptualization (Equal), Data curation (Equal), Investigation (Equal), Writing – review & editing (Equal) Mark V. Erdmann : Funding acquisition (Equal), Investigation (Equal), Resources (Equal), Writing – review & editing (Equal) Lisa A. Hoopes : Funding acquisition (Equal), Investigation (Equal), Resources (Equal), Writing – review & editing (Equal) Christine L. Dudgeon : Conceptualization (Equal), Writing – review & editing (Equal) Matthew D. Dunbabin : Investigation (Equal), Methodology (Equal), Resources (Equal), Writing – review & editing (Equal) Alistair D. M. Dove : Conceptualization (Equal), Funding acquisition (Equal), Investigation (Equal), Methodology (Equal), Resources (Equal), Writing – review & editing (Equal) Robin J. Beaman : Data curation (Equal), Investigation (Equal), Resources (Supporting), Visualization (Supporting), Writing – review & editing (Equal) Samantha D. Reynolds : Investigation (Equal), Writing – review & editing (Equal) Christopher Rohner : Investigation (Equal), Writing – review & editing (Equal) Samuel M. Williams : Writing – review & editing (Equal) David Paton : Resources (Supporting), Writing – review & editing (Equal) Sonny Lewis : Investigation (Equal), Writing – review & editing (Equal) Adam Barnett : Conceptualization (Lead), Data curation (Equal), Funding acquisition (Lead), Investigation (Equal), Project administration (Lead), Resources (Equal), Writing – review & editing (Equal) firstpage\fancyhf \lhead \chead \rhead \cfoot فروردین ماه ۱۴۰۴ Figure A1: Global distribution of whale shark ( Rhincodon typus ) hotspots, with colours indicating sex-dominance and circle size representing the dominant maturity status at each site. The notable gap in the southwestern Pacific is marked with a “?”. The shaded green area represents the species’ range distribution, adapted from the IUCN Red List assessment (Pierce & Norman, 2016). Figure A2: Whale shark ( Rhincodon typus ) sightings recorded on the east coast of Australia from public data bases, social media, and anecdotal reports, excluding duplicated records. A) Annual whale shark sightings from 2007 and 2018, and monthly distribution of sightings for individual sharks, groups, and all sharks in B), C), and D), respectively. Figure A3: Westerly-looking 3D view of the Great Barrier Reef, Australia. Bathymetry data courtesy of the Schmidt Ocean Institute and Australian Hydrographic Office. Table A1: Photo IDs of Wreck Bay whale sharks ( Rhincodon typus ) submitted to Sharkbook: Wildbook for Sharks (https://www.sharkbook.ai). For individuals that were also satellite tagged, the corresponding Platform Transmitter Terminal (PTT) ID is provided. GBR-001 M 700 2021 178951 9cf2da54-28d2-448b-acfa-ea285aec362c GBR-002 M 550 2021 8eae9454-2301-435b-96b4-dfd4c3f6f6c5 GBR-003 F 500 2021 c9834549-ac87-4903-ae74-6f8f434969d7 GBR-004 M 650 2021 2c448119-5cfe-4476-8b73-246c01be5e24 GBR-005 M 700 2021 9968c8a9-b0bc-45ef-8940-757a0db4cbd4 GBR-006 F 600 2021 178954 000588bf-460f-49c7-99b9-fe9a0801640f GBR-007 F 600 2021 178957 83bb78b7-8d13-41e5-b7c3-56061ba8ecee GBR-008 F 600 2021 a5c08b42-90d2-4ef6-b4a0-3214fc51d133 GBR-009 M 600 2021 178953 46c4f0dc-6306-4b1d-bd97-33d6c31f8126 GBR-010 F 550 2021 178950 a9697a0e-5837-4673-b299-1dcdeceb5215 GBR-044 F 600 2023 63921607-6cc3-4123-9b7e-38f6f0651642 GBR-045 F 450 2023 270a7a9a-c98e-425f-967c-24439723414c GBR-046 M 700 2023 243951 219a61d9-c57f-4319-a06f-c2854c681e2a GBR-047 M 700 2023 252324 5803be05-89e5-49b8-a917-e23ad069c9c0 GBR-048 M 550 2023 0350e4b7-2d90-4aba-a6c1-817b981cdeff GBR-049 M 600 2023 252325 40ffbc23-2cd3-4979-854e-5574413257f3 GBR-050 M 600 2023 243953 06c0fccf-d4c9-4c37-ab8b-2127332a1a59 GBR-051 M 800 2023 243952 4b093b96-e374-4071-a16a-6e1a100f3f77 GBR-052 M 450 2023 aee3c3e3-69ed-4e41-8e06-4d30c483f317 GBR-053 M 700 2023 176409 d7ffb68e-1196-41de-a54e-42a495a0101b GBR-054 M 450 2023 2307868c-6d50-48b6-95ee-a0a876fe81f7 GBR-055 F 650 2023 0af57755-623c-4eb8-8e6d-8c3c9999a108 GBR-056 M 675 2023 243954 3217982d-c99c-4b0b-a0f7-0c2a11a7bddd GBR-057 F 650 2023 588c7359-2d45-418c-9eb2-449f622495a3 GBR-058 M 600 2023 380dc23f-082c-4411-82b4-fe85f299dec0 GBR-059 M 650 2023 243955 f218f87b-236c-461a-9f46-22c28de20dc6 GBR-060 M 400 2023 3283160e-b863-4a60-b008-0bb405b1432e GBR-061 M 400 2023 d568e7df-3664-4ffe-af25-7ab76858336a GBR-066 M 400 2019 176413 2a696b10-69a7-43c7-945b-dd937884b615 GBR-067 U 400 2019 176407 b5c2190e-d2f0-4aa1-93d8-f18c96b252b3 GBR-068 M 750 2019 178948 c85aa324-012b-42df-9d93-953b4de5e787 GBR-069 M 700 2019 178949 bee933e8-d64b-4d95-8556-db45c182c71a GBR-070 M 650 2024 42013657-cc6d-458e-8261-80663a12bc99 GBR-011 F 650 2024 f7ad700e-9451-48f8-a432-9d5a5eda574e GBR-012 M 700 2024 a27859fe-7e44-4a2f-b63a-75228af397cf GBR-013 M 750 2024 9749edd8-6680-4313-84de-e3ef0794e9ca GBR-014 F 400 2024 bb46a7e1-de88-4207-b924-99da76346faa GBR-015 M 700 2024 1d4b768d-eb3c-4576-b97f-aead6f2d3357 GBR-016 M 500 2024 8b3ac1f7-93c0-4db6-8d11-d4677279a7b5 GBR-017 M 800 2024 a754f8b0-98fb-4b29-a302-c44036ebf112 GBR-018 M 700 2024 43c74038-d691-4f28-85ff-65b3f1aae0ae GBR-019 M 750 2024 7b1e4b87-4a7b-4598-9b6a-f2b51bc2020d GBR-020 F 600 2024 19c9da71-0f84-48aa-98aa-c1b647ae39f5 GBR-021 M 600 2024 8fa5eec0-cabb-45da-99e9-cb12db42a6c3 GBR-023 M 650 2024 617a8fb0-bf86-4847-8c72-a47b4fab57c9 GBR-024 M 450 2024 285aa49d-337d-4817-9132-87fcbed12e58 GBR-025 M 500 2024 5ed483c0-f15d-46c1-868b-649a53271b2a GBR-026 M 500 2024 1865e936-67d5-48da-9dee-ae81bc0fc42e GBR-027 M 700 2024 2fbff285-4245-4c96-939d-5abab875aefc GBR-028 M 800 2024 2d345183-6054-4d1f-901a-01bb6b09c515 GBR-029 M 500 2024 a3312908-56e7-4a49-8284-70e5097b960e GBR-030 M 700 2024 841a944c-f9e2-4acd-8b41-3cbc67d654bd GBR-031 M 700 2024 31d73cc9-2125-4180-9899-de682e46b3a3 GBR-032 M 600 2024 b2b57440-db1a-4dbe-a647-c8d2f1a403de GBR-033 M 600 2024 37fc2977-91c1-4f65-94c9-370a5a37d001 GBR-034 M 500 2024 9e8d7286-941f-4744-8413-fc044a5b2f87 GBR-035 M 700 2024 b9124650-d9d8-40cc-8010-939b56d35abc GBR-036 F 350 2024 c2034778-7ae1-4265-a9eb-7d5b9d013669 GBR-037 M 500 2024 ec557c0b-9113-49d7-91ec-5cb17146b73a PTT = platform transmitter terminal Table A2: Meta data of tagged whale sharks on the east coast of Australia, including their respective number of locations transmitted, days at liberty (DAL), and track distance in km. U = undetermined. 1 172899 2018-10-24 U 500 SPOT-253 Tether 185 146 3670 2 176413 2019-11-17 M 400 SPOT-257 Fin Clamp 81 88 2672 3 176407 2019-11-18 U 400 SPOT-257 Fin Clamp 9 6 18 4 178948 2019-11-19 M 750 SPOT-257 Fin Clamp 73 39 255 5 178949 2019-11-19 M 700 SPOT-257 Fin Clamp 11 3 20 6 178951 2021-12-05 M 700 SPOT-257 Fin Clamp 29 37 865 7 178953 2021-12-05 M 600 SPOT-257 Fin Clamp 461 158 4298 8 178957 2021-12-06 F 600 SPOT-257 Fin Clamp 84 526 1934 9 178954 2021-12-06 F 600 SPOT-257 Fin Clamp 333 770 11355 10 172900 2023-11-03 U 510 SPOT-253 Tether 235 132 2638 11 243951 2023-11-30 M 700 SPOT-196 Fin Clamp 57 7 143 12 252324 2023-11-30 M 700 SPLASH10-346 Fin Clamp 509 397 6067 13 243953 2023-12-01 M 600 SPOT-196 Fin Clamp 22 5 76 14 243952 2023-12-01 M 800 SPOT-196 Fin Clamp 126 68 1843 15 252325 2023-12-01 M 600 SPLASH10-346 Fin Clamp 280 97 1538 16 243954 2023-12-01 M 650 SPOT-196 Fin Clamp 78 73 643 17 176409 2023-12-02 M 700 SPOT-253 Fin Clamp 28 9 1388 18 243955 2023-12-04 M 650 SPOT-196 Fin Clamp 65 39 770 19 178950 a 2021-12-05 F 550 SPOT-253 Fin Clamp 1 0 a a Tag failed – excluded from analysis; only used for demographic analysis. PTT = platform transmitter terminal Table A3: Details on parameters set in the clustering process for determination of shifts in behaviour in whale shark ( Rhincodon typus ) tracking data using segclust2d package (Patin et al., 2020). For each shark (PTT), the minimum date and date of leaving the Wreck Bay (WB) aggregation area with clear shift in behaviour, the number of days spent within the aggregation area until leaving, and the number of locations transmitted during that time are given. For animals and periods where a clear arrival date in the WB area is apparent, the minimum Dates are marked with an asterisk. \fancypagestyle firstpage\fancyhf \lhead \chead \rhead \cfoot فروردین ماه ۱۴۰۴ 172899 Speed (smoothed), turning angle 10 3 11/11/2018 * 25/11/2018 14 10 172900 Speed (smoothed), turning angle 10 4 06/12/2023 * 09/01/2024 34 63 176407 19/11/2019 Has not left 6 9 176409 First location away from WB and no area-restricted search behaviour obvious ? 176413 X, Y 5 5 17/11/2019 18/01/2020 17 32 178948 19/11/2019 Has not left 39 63 178949 20/11/2019 Has not left 3 10 178951 X, Y 5 3 05/12/2021 17/12/2021 13 11 178953 X, Y 10 5 05/12/2021 12/12/2021 7 14 178954 X, Y 5 5 Year 1: 06/12/2021 25/12/2021 Year 2: 14/11/2022 * 25/11/2022 Year 3: 03/11/2023* 25/12/2023 19 11 40 23 7 60 178957 X, Y 5 5 06/12/2021 29/12/2021 23 17 243951 30/11/2023 Has not left 7 53 243952 X, Y 5 3 02/12/2023 2/12/2023 22 76 243953 01/12/2023 Has not left 5 18 243954 X, Y 5 3 01/12/2023 13/01/2024 43 45 243955 X, Y 5 3 04/12/2023 25/12/2023 21 45 252324 X, Y 10 3 Year 1: 30/11/2023 26/12/2023 Year 2: 24/10/2024 23/11/2024 27 30 145 55 252325 X, Y 10 5 01/12/2023 12/12/2023 11 49 PTT = platform transmitter terminal Table A4: Population kernel density estimates (PKDE) for whale sharks ( Rhincodon typus ) aggregating in the vicinity of Wreck Bay. \fancypagestyle firstpage\fancyhf \lhead \chead \rhead \cfoot فروردین ماه ۱۴۰۴ low high 95% (home range) 5,335.8 17.9 24,411.1 50% (core area) 815.5 2.7 3,730.9 25% (high intensity core area) 238.3 0.8 1,090.0 Supplementary Material File (fig_a3.pdf) Download 14.16 MB File (image10.emf) Download 16.89 MB References 1. https://doi.org/10.3354/esr01293 https://doi.org/10.2307/1543512 https://doi.org/10.1371/journal.pone.0102060 https://doi.org/10.1016/j.anbehav.2015.09.019 https://doi.org/10.3389/fmars.2022.775691 https://doi.org/10.1111/j.1365-2664.2005.01117.x https://doi.org/10.1002/aqc.3087 https://doi.org/10.4225/25/5a207b36022d2 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Collection Ecology and Evolution Keywords description ecological experiment ecosystem marine population ecology vertebrate Authors Affiliations Ingo Miller 0000-0002-9406-2012 [email protected] James Cook University College of Science and Engineering View all articles by this author Richard Fitzpatrick Biopixel Oceans Foundation View all articles by this author Kátya Gisela Abrantes Biopixel Oceans Foundation View all articles by this author Brad Norman ECOCEAN Inc. View all articles by this author Simon Pierce Marine Megafauna Foundation View all articles by this author Mark Erdmann Conservation International Aotearoa View all articles by this author Lisa Hoopes Georgia Aquarium Inc View all articles by this author Christine Dudgeon Biopixel Oceans Foundation View all articles by this author Matthew Dunbabin Biopixel Oceans Foundation View all articles by this author Alistair Dove Georgia Aquarium Inc View all articles by this author Robin Beaman James Cook University College of Science and Engineering Cairns Campus View all articles by this author Samantha Reynolds ECOCEAN Inc. View all articles by this author Christopher Rohner Marine Megafauna Foundation View all articles by this author Samuel Williams Queensland Department of Agriculture and Fisheries View all articles by this author David Paton Blue Planet Marine View all articles by this author Sonny Lewis ECOCEAN Inc. View all articles by this author Adam Barnett Biopixel Oceans Foundation View all articles by this author Metrics & Citations Metrics Article Usage 893 views 219 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Ingo Miller, Richard Fitzpatrick, Kátya Gisela Abrantes, et al. The Needle in the Haystack: Uncovering the First Whale Shark ( Rhincodon typus ) Aggregation in the Southwest Pacific. Authorea . 04 April 2025. DOI: https://doi.org/10.22541/au.174375799.97408243/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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