Christine L Dudgeon

Understanding the drivers of megafauna aggregations is critical for managing threatened species in a changing climate. We analysed an 18-year dataset (2007–2024) of reef manta ray (Mobula alfredi) abundance and zooplankton density at Hanifaru Bay, Maldives (5.1733°N, 73.145°E) —the world's largest known manta ray aggregation. Generalised Linear Models were used to evaluate sightings against local environmental variables and broad-scale climatic indices. Results reveal that interannual abundance was modulated by the Indian Ocean Dipole, with sightings and prey density reaching decadal highs during the record Negative Indian Ocean Dipole and La Niña of 2021–2022. Locally, zooplankton density was the strongest predictor of M. alfredi abundance, explaining > 60% of the observed variation. Sightings were 25x higher during peak prey availability than during prey absence. Aggregations were timed with spring tides (peaking 2.7 hours post-high tide), new and full moon phases, and 25–35 km/h north-northwest winds. We also identified a critical thermal threshold at 28.6°C, beyond which sightings declined by 15.7% per degree of sea surface temperature warming. This sequence confirms that the local bathymetric retention mechanisms are dependent on specific regional oceanographic conditions. Our findings suggest that while Hanifaru Bay consistently concentrates zooplankton biomass, its functional utility as a foraging hotspot is vulnerable to climate-driven shifts in the Indian Ocean Dipole and rising sea surface temperatures, which may decouple the predator from its primary nutrient supply.

Walking sharks (Hemiscyllium) comprise 9 morphologically similar species whose identification relies on distinctive color patterns, genetic markers, and geographically restricted distributions. The genus is endemic to Australia and the island of New Guinea, a region that coincides with the global hotspot for carpet shark diversity (Orectolobiformes) that has been shaped by complex tectonic and sea‑level histories. Although knowledge of walking shark distributions has been updated over the past two decades, the species endemic to eastern Papua New Guinea remain poorly known. This study addresses these gaps by investigating the distributions of walking sharks in eastern Papua New Guinea. We used a series of in-situ surveys to review the ranges of walking shark species and to document their species-specific color patterns, complemented by an assessment of genetic markers to confirm the updated geographical distributions across species and explore phylogeographic patterns in the region. We present updated distributions for two species (H. michaeli and H. hallstromi)¸ as well as a theory for the development of a mosaic of disjunct, non-overlapping distributions previously unreported for the genus. Additionally, we describe a tenth member of the genus, Hemiscyllium dudgeonae, n. sp., which is likely to be highly threatened. We present possible mechanisms that may have produced this mosaic of distributions and influenced speciation in the region. Finally, we discuss the conservation implications of these findings.

A Field Guide to the Vertebrates of Lady Elliot Island was created to capture a living snapshot of life on and around this remarkable coral cay. As ocean temperatures shift and species move into new areas, understanding what’s here now is the first step in tracking change. This guide provides that essential benchmark.

Developed through the Leaf to Reef research project, the book brings together years of scientific surveys alongside invaluable sightings from resort staff and passionate citizen scientists. The result? New records for Australian waters, documented range extensions, and even species new to science.

Inside, you’ll find vibrant full-colour photographs and accessible species profiles covering birds, sharks, rays, fishes, mammals, and reptiles. Special “creature features” spotlight some of Lady Elliot Island’s most iconic wildlife, including red-tailed tropicbirds, reef manta rays, Lady Elliot shrimpgobies, humpback whales, and green sea turtles.

More than a field guide, this book is a celebration of collaboration, discovery, and the extraordinary biodiversity of the southern Great Barrier Reef — a vital resource for anyone who wants to explore and understand this changing marine world.

Zooplankton are vital links in marine food webs, yet their biomass remains challenging to quantify across broad spatial and temporal scales. This study introduces the Zooplankton Visual Index–a simple, rapid and scalable semi-quantitative method for evaluating zooplankton biomass through underwater observations. Following the establishment of a standardized protocol, validation against in situ net samples demonstrated that index levels increased consistently with measured biomass and predictable shifts in community composition. We then applied the validated index to a 9-year dataset of reef manta ray (Mobula alfredi) sightings in the Maldives. Increased M. alfredi abundance significantly correlated with higher index levels, confirming that the index effectively captures the food environment as an important predictor of behavior and habitat use. Thus, the Zooplankton Visual Index provides an accessible and validated tool for assessing prey availability, enabling researchers, non-specialist field staff and citizen science programs to contribute to broad-scale ecological research and conservation efforts for marine megaplanktivores.

The Asia region harbors exceptional chondrichthyan (shark, ray, and chimaera) diversity but faces intense fishing pressure. The Important Shark and Ray Area (ISRA) process provides a collaborative, evidence-based framework to identify critical habitats and inform spatial management. We assessed ISRAs across the Bay of Bengal, Southeast Asia, and the Northwest Pacific to characterize their extent, ecological significance, and conservation relevance. We delineated 122 ISRAs spanning ~ 1 million km2 (~ 3% of the region) across 12 jurisdictions and international waters, encompassing habitats for 121 species (~ 30% of Asia’s chondrichthyans), 76% of which are threatened. Depleted taxa (e.g., giant guitarfishes, Glaucostegidae) were represented, but charismatic megafauna (e.g., Whale Shark Rhincodon typus) were overrepresented. In contrast, deepwater and freshwater species were underrepresented. Reproductive Areas were the most common ISRA sub-criterion applied (52% of ISRAs), largely in nearshore zones, while areas for range-restricted species were less frequently (18%) identified. Twelve ISRAs overlapped with biodiversity hotspots, including seven in areas of high overall chondrichthyan species richness and five in areas of high range-restricted species richness. Citizen science was the predominant research method used to delineate ISRAs, while fisheries data were underused despite the region’s major fisheries footprint. Geographic coverage was uneven: Indonesia held the most ISRAs (n = 40; 71.7% of ISRA coverage) while eight jurisdictions (e.g., Viet Nam, China, Republic of Korea) lacked ISRAs due to data gaps. Protection shortfalls are stark: MPAs cover < 5% of national waters in 16 jurisdictions (eight with < 1%); 5.4% of ISRA area lies within MPAs; and only 2.8% of ISRA spatial extent overlaps with no-take zones. These results provide a regional foundation to guide spatial planning, prioritize management, close data gaps, and support recovery of Asia’s diverse and imperiled chondrichthyan assemblages.

Population connectivity shapes both genetic and cultural variation, including in learned vocal behaviors such as birdsong. Silvereyes (Zosterops lateralis) are well-known island colonizers, providing a useful model for examining how cultural evolution unfolds across populations with differing geographic isolation. We compared song dialects from 4 populations in South East Queensland: 2 mainland (Z. l. cornwalli) and 2 island populations (Z. l. chlorocephalus), for which patterns of genetic connectivity had previously been described. From field recordings, we constructed syllable repertoires and measured spectral features to quantify dialect structure and acoustic divergence. We found no correlation between acoustic distance and either genetic or geographic distance among populations, indicating that dialect divergence is not strongly constrained by neutral genetic structure or spatial separation at this scale. Island populations showed greater similarity to one another, as well as slightly higher syllable diversity, than mainland populations. These patterns are consistent with cultural divergence shaped by local, social, or ecological conditions rather than by geographic or genetic distance. Our findings refine current understanding of island dialect evolution in silvereyes by showing that cultural differentiation can occur despite limited genetic divergence and relatively small geographic distances. Because song is socially transmitted, cultural traits may respond rapidly to environmental change, suggesting that conservation strategies for island passerines may benefit from integrating the cultural dimensions of avian behavior.

Like most seabirds, red-tailed tropicbirds (Phaethon rubricauda) spend most of their lives at sea, returning to islands only to breed. Despite their well-known capacity for long-distance movement, little is known about how new colonies are established or how genetic diversity is maintained across isolated, highly philopatric breeding populations. Here, we investigate patterns of genetic diversity using SNP genotyping across three breeding colonies forming a triangular spatial configuration between the Great Barrier Reef and Ashmore Reef in the eastern Indo-Pacific. We focus first on Lady Elliot Island, the most recently colonised site in the region, and compare it to Raine Island (the only other Great Barrier Reef colony), and Ashmore Reef off north-western Australia. Red-tailed tropicbirds were first recorded nesting on Lady Elliot Island in the 1980s, following revegetation efforts after historical guano mining. Raine Island lies approximately equidistant from Lady Elliot Island (1965 km south) and Ashmore Reef (2280 km west). Despite its smaller size, the Lady Elliot Island colony exhibited genetic diversity that was greater than the larger Raine Island colony and comparable to the larger Ashmore Reef colony. Weak genetic population structuring was observed between the three colonies, with Raine Island positioned between the other two in a pattern consistent with their geographic layout. These findings suggest well-established connectivity among colonies, with Lady Elliot and Ashmore Reef populations likely drawing from a broader genetic pool. Further sampling across the Indian and Pacific Oceans may reveal additional drivers of genetic structure.

Monitoring cetaceans in Australia's Great Barrier Reef (GBR) is essential for understanding their ecological roles and informing conservation, yet traditional visual surveys are limited by logistical constraints. Passive acoustic monitoring (PAM) offers a complementary solution, particularly in acoustically complex coral‐reef habitats of the southern GBR. Over 2 years, we deployed an autonomous recorder at Lady Elliot Island to document cetacean presence and assess environmental associations. We detected vocalizations from humpback whales ( Megaptera novaeangliae ), dwarf minke whales ( Balaenoptera acutorostrata subsp.), and delphinids, likely spinner ( Stenella longirostris ) and/or bottlenose dolphins ( Tursiops spp.). Humpback whale song dominated recordings from June through October, while dwarf minke whale “Star‐Wars” calls occurred from May to August, marking the first acoustic evidence of this subspecies within the southern GBR. Dwarf minke whale detections correlated positively with chlorophyll‐ a concentration, whereas humpback whale detections were negatively associated with wind speed. Rorqual vocalizations declined during periods of elevated anthropogenic noise, while odontocete detections remained unaffected. These results highlight PAM's effectiveness for detecting cetaceans within complex reef soundscapes and suggest acoustic niche partitioning among taxa. These critical baseline data inform management strategies for understudied GBR cetacean populations and establish a robust framework for future long‐term monitoring efforts and effective conservation actions.

Marine megafauna species are affected by a wide range of anthropogenic threats. To evaluate the risk of such threats, species' vulnerability to each threat must first be determined. We build on the existing threats classification scheme and ranking system of the International Union for Conservation of Nature (IUCN) Red List of Threatened Species by assessing the vulnerability of 256 marine megafauna species to 23 at-sea threats. The threats we considered included individual fishing gear types, climate-change-related subthreats not previously assessed, and threats associated with coastal impacts and maritime disturbances. Our ratings resulted in 70 species having high vulnerability (v > 0.778 out of 1) to at least 1 threat, primarily drifting longlines, temperature extremes, or fixed gear. These 3 threats were also considered to have the most severe effects (i.e., steepest population declines). Overall, temperature extremes and plastics and other solid waste were rated as affecting the largest proportion of populations. Penguins, pinnipeds, and polar bears had the highest vulnerability to temperature extremes. Bony fishes had the highest vulnerability to drifting longlines and plastics and other solid waste; pelagic cetaceans to 4 maritime disturbance threats; elasmobranchs to 5 fishing threats; and flying birds to drifting longlines and 2 maritime disturbance threats. Sirenians and turtles had the highest vulnerability to at least one threat from all 4 categories. Despite not necessarily having severe effects for most taxonomic groups, temperature extremes were rated among the top threats for all taxa except bony fishes. The vulnerability scores we provide are an important first step in estimating the risk of threats to marine megafauna. Importantly, they help differentiate scope from severity, which is key to identifying threats that should be prioritized for mitigation.

Reproductive behaviors in wild sharks remain largely undocumented, yet they are critical for understanding population dynamics and informing conservation strategies. The Indo-Pacific Leopard shark (Stegostoma tigrinum), listed as endangered by the IUCN, has primarily been studied in captivity, with little information on its natural mating behaviors. Here, we present the first documented observations of group copulation in free-living S. tigrinum, recorded at Abore Reef, New Caledonia. Our observations detail a sequential mating event involving two males and a single female over a 90-min period. The mating behavior followed a structured sequence, including prolonged pre-copulation positioning, male grasping of the female’s fins and tail, conspicuous siphon sac, copulatory thrusting, and clasper use consistent with previous reports from captive settings. These findings provide novel insights into the species’ reproductive strategies and highlight the importance of identifying and protecting key mating habitats. Given the conservation concerns surrounding S. tigrinum, understanding these mating mechanisms and recognizing reproductive sites are crucial for effective species management. Our study underscores the need for further field observations to better understand the reproductive ecology of S. tigrinum and support targeted conservation efforts. Digital video images related to the article are available at: http://www.momo-p.com/showdetail-e.php?movieid=momo250903st01a.