Brad Norman

Aim
To understand how natural geomorphological features and oil and gas platforms (OG platforms) influence the habitat use and seascape connectivity of the whale shark (Rhincodon typus).

Location
East-Indian Ocean and North-West Australia.

Methods
We compiled a satellite tracking dataset of 78 whale sharks tagged across a 14-year period at Ningaloo Reef and Shark Bay World Heritage Areas in Western Australia to develop spatial networks for the regions of the East-Indian Ocean and North-West Australia. We then applied a Bayesian modelling framework to assess the effects of natural features and OG platforms on spatial patterns and habitat connectivity.

Results
Geomorphological features such as pinnacles, canyons, and seamounts promoted habitat connectivity and strongly influenced the habitat use of whale sharks across both regional (1000's km; East-Indian Ocean) and local (100's km; North-West Australia) spatial scales. In the North-West of Australia, OG platforms had similar effects on habitat use as natural feature types and also enhanced habitat connectivity. The OG platforms most visited by whale sharks were situated close to the edge of the continental shelf and near natural geomorphological features that likely enhance productivity.

Main Conclusion
Our work identified natural geomorphological features that promoted habitat use and connectivity for whale sharks across oceanic and coastal seascapes. Sharks routinely visited OG platforms, which acted as migratory stepping stones that further enhanced habitat connectivity. Protection of natural feature types that promote habitat use and connectivity could assist conservation management of whale sharks. We suggest that the influence of OG platforms on their movement and habitat use beyond individual structures, should be considered in environmental impact assessments during operation and decommissioning phases.

The expansion of the world's merchant fleet poses a great threat to the ocean's biodiversity. Collisions between ships and marine megafauna can have population-level consequences for vulnerable species. The Endangered whale shark (Rhincodon typus), shares a circumglobal distribution with this expanding fleet and tracking of movement pathways has shown that large vessel collisions pose a major threat to the species. However, it is not yet known whether they are also at risk within aggregation sites, where up to 400 individuals can gather to feed on seasonal bursts of planktonic productivity. These “constellation” sites are of significant ecological, socio-economic and cultural value. Here, through expert elicitation, we gathered information from most known constellation sites for this species across the world (>50 constellations and >13,000 individual whale sharks). We defined the spatial boundaries of these sites and their overlap with shipping traffic. Sites were then ranked based on relative levels of potential collision danger posed to whale sharks in the area. Our results showed that researchers and resource managers may underestimate the threat posed by large ship collisions due to a lack of direct evidence, such as injuries or witness accounts, which are available for other, sub-lethal threat categories. We found that constellations in the Arabian Sea and adjacent waters, the Gulf of Mexico, the Gulf of California, and Southeast and East Asia, had the greatest level of vessel collision threat. We also identified 39 sites where peaks in shipping activity coincided with peak seasonal occurrences of whale sharks, sometimes across several months. Simulated potential collision mitigation options estimated a minimal impact to industry, as most whale shark core habitat areas were relatively small. Given the threat posed by vessel collisions, a coordinated, multi-national approach to collision mitigation is needed within priority whale shark habitats to ensure collision protection for the species.

Wildlife tourism can benefit conservation of target species, however, it can have detrimental effects on animal behaviour and physiology. Whale shark Rhincodon typus tourism has seen recent rapid growth globally, but methods and regulations vary widely. Ningaloo Reef, Australia is considered “gold standard” whale shark tourism management due to legal regulation, strict enforcement, and high compliance. Rather than relying on observational data, we used biotelemetry to collect high-resolution data (20 Hz) on whale sharks’ movement behaviour in the presence or absence of tourists. Tourism encounters lasted an average of 62 min and swimming with tourists increased the activity levels of larger (> 7 m) but not smaller sharks. Given that activity levels positively correlate with energetic costs, it is likely the 18% increase seen in activity of large sharks would have incurred additional energetic costs. However, when considered as a proportion of daily energy requirements, these additional costs were only incurred for an average of 4% of a whale shark’s day. The tourism-induced impacts we found on the endangered whale sharks at this highly regulated tourism site would not have been apparent from purely observational studies, highlighting the utility of biotelemetry to quantify tourism-related impacts on wildlife.

Context. Shipping impacts are a major environmental concern that can affect the behaviour and health of marine mammals and fishes. The potential impacts of shipping within marine parks is rarely considered during the planning process. Aims. We assessed the areal disturbance footprint of shipping around Australia, its overlap with marine parks, and known locations of megafauna, so as to identify areas of concern that warrant further investigation. Methods. Automatic Identification System (AIS) shipping data from 2018 to 2021 were interpreted through a kernel-density distribution and compared with satellite data from & SIM;200 individuals of megafauna amalgamated from 2003 to 2018, and the locations of marine parks. Key results. Over 18% of marine parks had shipping exposure in excess of 365 vessels per year. Around all of Australia, 39% of satellite-tag reports from whale shark and 36.7% of pygmy blue and humpback whale satellite-tag reports were in moderate shipping-exposure areas (> 90 ships per year). Shipping exposure significantly increased from 2018 despite the pandemic, including within marine parks. Conclusions. These results highlight the wide-scale footprint of commercial shipping on marine ecosystems that may be increasing in intensity over time.

As the use of coastal and offshore environments expands, there is a need to better understand the exposure of marine megafauna to anthropogenic activities that potentially threaten their populations. Individual satellite telemetry studies are often hampered by small sample sizes, providing limited information on spatiotemporal distributions of migratory animals and their relationships to anthropogenic threats. We addressed this issue by synthesising satellite tracking data from 484 individuals of three taxonomic groups and six species; three marine turtle, two whale and one shark. The spatial overlap between taxa distributions and multiple anthropogenic activities was assessed as a proxy for the cumulative exposure of these taxa to anthropogenic threats (coastal modification, vessel strike, underwater noise, oil spill, bycatch, entanglement, and artificial light) across an area totalling 2,205,740 km2 off north-western Australia. Core exposure areas (top 50% of the distribution) encompassed ecologically important sites for all taxa, such as the Ningaloo and Pilbara regions, migratory routes for whales and sharks in offshore waters beyond Ningaloo Reef, and marine turtle nesting beaches at Barrow Island and Cape Lambert. Although areas of high exposure represented <14% of taxa distributions, we showed that no taxa occurred in the absence of threats and that even areas with existing spatial protections are experiencing high levels of exposure. Importantly, we developed a robust approach for documenting the potential exposure of marine species to a range of human activities at appropriate spatial scales to inform conservation management.

A new microbothriid monogenean Dermopristis pterophilus n. sp. is described from the skin of the Critically Endangered green sawfish Pristis zijsron Bleeker, 1851 in the Ashburton River delta, northern Western Australia. Analyses of the 28S ribosomal DNA marker and the molecular barcoding markers Histone 3 and Elongation Factor 1 α confirmed position among the Microbothriidae, with close affinity to the only other sequenced representative of Dermopristis Kearn, Whittington and Evans-Groing, 2010. The new species is morphologically consistent with the concept of Dermopristis; it has two testes, lacks a male copulatory organ and has a simple haptor. It is smaller than its two congeners D. paradoxus Kearn, Whittington and Evans-Gowing, 2010 and D. cairae Whittington and Kearn, 2011 and is most similar to the former, distinguished only in that it lacks the strong, transverse, parallel ridges on the ventral body surface that characterise that species. It is more easily distinguished from D. cairae, differing in body shape, possession of a seminal receptacle, and relative position and size of the haptor. It may further differ from both species by fine details of the gut diverticula, although these details are difficult to ascertain. Spermatophores were observed in the new species, similar to those previously reported for D. cairae. The new species exhibits site attachment preference: infections were greatest on and immediately adjacent to the host pelvic fins (including male reproductive organs, i.e. claspers), moderate in proximity to the dorsal and pectoral fins, few on the caudal fin and peduncle, and infrequently, isolated worms occurred elsewhere on the dorsal and ventral surfaces of the body. There was no incidence of infection on the head (including rostrum). We presume D. pterophilus is restricted to P. zijsron and thus likely faces the same threat of extinction.

Travel represents a major cost for many animals so there should be selection pressure for it to be efficient – at minimum cost. However, animals sometimes exceed minimum travel costs for reasons that must be correspondingly important. We use Dynamic Body Acceleration (DBA), an acceleration-based metric, as a proxy for movement-based power, in tandem with vertical velocity (rate of change in depth) in a shark (Rhincodon typus) to derive the minimum estimated power required to swim at defined vertical velocities. We show how subtraction of measured DBA from the estimated minimum power for any given vertical velocity provides a “proxy for power above minimum” metric (PPAmin), highlighting when these animals travel above minimum power. We suggest that the adoption of this metric across species has value in identifying where and when animals are subject to compelling conditions that lead them to deviate from ostensibly judicious energy expenditure.

Conservation and management of mobile marine species requires an understanding of how movement behaviour and space-use varies among individuals and populations, and how intraspecific differences influence exposure to anthropogenic threats. Because of their long-distance movements, broad distribution and long lifespan, whale sharks (Rhincodon typus) can encounter multiple, cumulative threats. However, we lack knowledge on how sharks at different aggregations use their habitats, and how geographic variation in anthropogenic threats influences their vulnerability to population decline. Using movement data from 111 deployments of satellite-linked tags, we examined how whale sharks at five aggregations in the Indian Ocean varied in their exposure to six anthropogenic impacts known to threaten this endangered species. Tagged sharks were detected in territorial waters of 24 countries, and international waters, with individuals travelling up to 11,401 km. Despite long-distance movements, tagged sharks from each aggregation occupied mutually exclusive areas of the Indian Ocean, where they encountered different levels of anthropogenic impacts. Sharks in the Arabian Gulf had the greatest proximity to oil and gas platforms, and encountered the warmest sea surface temperatures and highest levels of shipping, pollution and ocean acidification, while those from the Maldives and Mozambique aggregations had the highest exposure to fishing and human population impacts respectively. Our findings highlight the need for aggregation-specific conservation efforts to mitigate regional threats to whale sharks. Multinational coordination is essential for implementing these efforts beyond national jurisdictions and tackling issues of global conservation concern, including the consequences of climate change and an expanding human population.

The world’s largest extant fish, the whale shark Rhincodon typus, is one of the most-studied species of sharks globally. The discovery of predictable aggregation sites where these animals gather seasonally or are sighted year-round – most of which are coastal and juvenile-dominated – has allowed for a rapid expansion of research on this species. The most common method for studying whale sharks at these sites is photographic identification (photo-ID). This technique allows for long-term individual-based data to be collected which can, in turn, be used to evaluate population structure, build population models, identify long-distance movements, and assess philopatry and other population dynamics. Lagged identification rate (LIR) models have fewer underlying assumptions than more traditional capture mark recapture approaches, making them more broadly applicable to marine taxa, especially far-ranging megafauna species like whale sharks. However, the increased flexibility comes at a cost. Parameter estimations based on LIR can be difficult to interpret and may not be comparable between areas with different sampling regimes. Using a unique data-set from the Philippines with ~8 years of nearly continuous survey effort, we were able to derive a metric for converting LIR residency estimates into more intuitive days-per-year units. We applied this metric to 25 different sites allowing for the first quantitatively-meaningful comparison of sightings-derived residence among the world’s whale shark aggregations. We validated these results against the only three published acoustic residence metrics (falling within the ranges established by these earlier works in all cases). The results were then used to understand residency behaviours exhibited by the sharks at each site. The adjusted residency metric is an improvement to LIR-based population modelling, already one of the most widely used tools for describing whale shark aggregations. The standardised methods presented here can serve as a valuable tool for assessing residency patterns of whale sharks, which is crucial for tailored conservation action, and can cautiously be tested in other taxa.

Marine traffic is increasing globally yet collisions with endangered megafauna such as whales, sea turtles, and planktivorous sharks go largely undetected or unreported. Collisions leading to mortality can have population-level consequences for endangered species. Hence, identifying simultaneous space use of megafauna and shipping throughout ranges may reveal as-yet-unknown spatial targets requiring conservation. However, global studies tracking megafauna and shipping occurrences are lacking. Here we combine satellite-tracked movements of the whale shark, Rhincodon typus, and vessel activity to show that 92% of sharks’ horizontal space use and nearly 50% of vertical space use overlap with persistent large vessel (>300 gross tons) traffic. Collision-risk estimates correlated with reported whale shark mortality from ship strikes, indicating higher mortality in areas with greatest overlap. Hotspots of potential collision risk were evident in all major oceans, predominantly from overlap with cargo and tanker vessels, and were concentrated in gulf regions, where dense traffic co-occurred with seasonal shark movements. Nearly a third of whale shark hotspots overlapped with the highest collision-risk areas, with the last known locations of tracked sharks coinciding with busier shipping routes more often than expected. Depth-recording tags provided evidence for sinking, likely dead, whale sharks, suggesting substantial “cryptic” lethal ship strikes are possible, which could explain why whale shark population declines continue despite international protection and low fishing-induced mortality. Mitigation measures to reduce ship-strike risk should be considered to conserve this species and other ocean giants that are likely experiencing similar impacts from growing global vessel traffic.