Adrian Gleiss

Deep dives are performed by a range of marine megafauna, yet their function remains poorly understood. Proposed functions include foraging, predator avoidance, and navigation, but limited fine-scale data have hindered rigorous testing of these hypotheses. Here, depth time-series data from eight recovered and 16 non-recovered satellite tags deployed on oceanic manta rays (Mobula birostris) in Indonesia, Peru, and New Zealand were examined to characterise extreme dives and identify their potential function. From a total of 46,945 dives, 79 extreme dives (>500 m) were recorded, 11 of which were documented from recovered tags and associated high sampling frequency. Extreme dives were distinguished by rapid descents (up to 2.9 m s⁻¹), brief horizontal “steps” at depth, gradually slowing ascents, and extended periods spent near the surface both before and after diving. Unlike typical foraging dives, no substantial bottom phase was observed, and vertical oscillations—expected if feeding at depth—were absent. Extreme dives also occurred more frequently with increasing distance from the continental shelf edge as well as preceding periods of high 72h distance travelled, indicating they may inform subsequent movements. We propose that extreme dives enable oceanic manta rays to survey the properties of the water column, likely gathering environmental cues—such as temperature, dissolved oxygen, or geomagnetic gradients—to guide navigation and/or the decision to leave or remain in a general area. In open-ocean environments where external reference points are absent, such costly but infrequent dives may provide critical information for long-distance movements. Our results offer new insights into the role of extreme diving behaviour in oceanic manta rays and highlight the importance of fine-scale data for understanding deep-diving behaviours in marine megafauna.

Habitat suitability models (HSMs) are popular statistical tools used to inform decision-making for conservation planning, using species location data to characterize species-environment relationships and identify important habitats. Suitable habitats may vary according to behavior-specific resource requirements (e.g., foraging, resting), yet HSMs generally ignore behavior because obtaining spatially explicit behavioral data from wild animals is challenging. As such, suitable habitats may be incorrectly identified, and processes determining habitat selection may be misinterpreted. Despite offering unprecedented behavioral insight, contemporary multi-sensor biologgers remain underutilized in this context. We incorporated behavior into HSMs using biologging data collected from adult flatback turtles Natator depressus (n = 42) at a macrotidal study site in Western Australia and subsequently identified and characterized suitable habitat for key in-water behaviors. Foraging and resting locations derived from high-resolution motion sensor data (e.g., accelerometer, magnetometer) coupled with animal-borne video and GPS data were combined with 10 environmental features (i.e., bathymetry, aspect, slope, terrain ruggedness, distance from the coast and currents from a bespoke hydrodynamic model of the study site). A series of random forest HSMs were implemented for each behavior, accounting for temporal variation in habitat use. Bathymetry, distance from the coast, and currents best determined both foraging and resting suitability, with observed differences in habitat selection between behaviors. Overall, spatiotemporal patterns of most suitable foraging and resting habitat were similar, with shallow (10-15 m deep) nearshore (5-10 km from the coast) waters most suitable for both behaviors; however, habitats nearest to the coast (<5 km) were more suitable for foraging than resting. Overall, for foraging and resting, as water level increased turtles selected increasingly nearshore habitats where current speed was low and more variable direction. Overlap between most suitable habitats and current spatial zoning at the study site varied both seasonally and with water level, likely reflecting strong tidal influence on distribution and hence highlighting considerable opportunity for dynamic management. Our approach facilitates mechanistic insight into habitat selection and is generalizable across behaviors, taxa, and study systems, advancing the application of biologging tools to enhance the utility of HSMs and providing crucial context for decision-makers in threatened species management.

This paper describes the first confirmed record of a mature female dwarf sawfish, Pristis clavata, based on the dissection of an individual from the Karajarri Indigenous Protected Area in northwestern Australia. The 307-cm female, found deceased on an intertidal sandflat in July 2024, was in the early stages of pregnancy, with large ova visible in both uteri. Counts of vertebral growth zones suggested an age of 12 years. This record provides the first empirical insights into female size- and age-at-maturity, longevity and reproductive biology of this Critically Endangered fish.

Home range size and metabolic rate of animals are theorized to scale in relation to body mass with similar exponents. This expectation has only been indirectly tested using lab-derived estimates of basal metabolic rate as proxies for field energy requirements. Therefore, it is unclear if existing theory aligns with observed patterns of home range scaling since field metabolic rates may scale differently than basal metabolic rates. We conducted the first direct field test of the relationship between home range and metabolic rate allometry. Using acoustic telemetry, we simultaneously measured the home range sizes and field metabolic rates of lemon sharks (Negaprion brevirostris) spanning one order of magnitude in body mass and compared the allometric scaling exponents of these traits. Similarity between allometric scaling exponents confirmed an expected strong association between metabolic rate and home range size. However, a nonsignificant but negative association between standard metabolic rate (SMR) and home range size suggests a complex relationship between metabolism and home range, contrasting previous assumptions of a positive relationship. Nevertheless, an overall positive association between home range size and total metabolic rate persisted, driven by a strong association between active energy expenditure and home range size. These findings underscore the intricate relationship between energetics and home range size, emphasizing the need for additional direct field investigations and the potential for modern tagging technologies to gather relevant data.

Very little is known about the reproductive behaviours of whale sharks ( Rhincodon typus ). Here, we describe field observations of courtship behaviour by a whale shark at Ningaloo Reef, Western Australia. We witnessed and recorded following and biting behaviours by a sexually mature male of a smaller female. Following and biting are common events during courtship and copulation of other species of elasmobranchs. Our observations are consistent with earlier reports of courting behaviours in whale sharks provided by fishers, the pilot of a light plane and observations of courtship by a sexually mature male towards females held in aquaria.

Nearshore environments represent important habitat for many marine vertebrates during their early-life stages. Globally, these coastal sites are impacted by human activities that have the potential to negatively impact biodiversity in ways we do not yet fully appreciate. To improve our understanding of the relevance of mangrove removal in tropical elasmobranch nursery grounds, we studied the globally Vulnerable lemon shark (Negaprion brevirostris) in a mangrove-fringed lagoon in Bimini, The Bahamas, following a decade of coastal development and habitat disruption. We used two years of acoustic telemetry detections and generalised linear mixed models (GLMMs) to evaluate the link between juvenile shark spatial behaviour and six features of their physical environment. AIC-adjusted model-averaged predictions of habitat selection demonstrated that distance from the central mangrove forest was the most important feature for sharks. After updating model averaging to account for overall preference for proximity to the central forest, we found that medium density seagrass was secondarily preferred over all other habitat types (bare sand, sargassum, urban and rocky outcrops, and deep water) within the core use area (probability of use ≥ 50 %). Locally, our results support including this core area in future marine protected area considerations. More broadly, in the face of rapid global population declines of many elasmobranchs and wide-spread habitat fragmentation in coastal marine nurseries, we identified widely applicable habitat features underpinning an area of high ecological significance for a threatened shark during a vulnerable life stage and outlined a habitat selection framework suitable for using marine vertebrate movement data as ecological indicators for future applied conservation.

An animal’s movement is influenced by a plethora of internal and external factors, leading to individual- and habitat-specific movement characteristics. This plasticity is thought to allow individuals to exploit diverse environments efficiently. We tested if the movement characteristics of white sharks Carcharodon carcharias differ across ontogeny and among habitats along the coast of Central California. In doing so, we elucidate how changes in internal state (physiological changes coinciding with body size) and external environments (differing seascapes and/or diel phases) shape the movement of this globally distributed predator. White sharks, from small juveniles to large adults, were equipped with motion-sensitive biologging tags at four contrasting seascapes: two islands, a headland, and an inshore cove. From multi-sensor biologging data, 20 metrics characterising movement were derived and subjected to multivariate analyses. Movement characteristics were most different across seascapes, followed by ontogeny and diel phase. Juvenile sharks, that were only encountered at the cove, displayed the most distinct movement characteristics. Sharks at this seascape remained close to the shore and were comparatively less active than sub-adult and adult sharks tagged elsewhere. Distinct night-time movements and dive patterns were recorded from sharks at an island seascape but not from those at the headland or inshore cove. The availability of prey and access to deeper water are likely drivers, with greater numbers of Northern elephant seals Mirounga angustirostris at the island seascapes and harbour seals Phoca vitulina at the headland seascape, while the offshore island group is also closer to the continental shelf edge. Juvenile sharks at the inshore cove are piscivorous and their habitat was not adjacent to pinniped haul out areas nor deeper water. This study demonstrates plasticity in the movements of a top predator, that adapts its routine to suit the habitat it forages within.

Wedgefishes have recently been recognised as one of the most imperilled marine fish families worldwide. However, many knowledge gaps about their biology and ecology hinder conservation efforts. Here we used a combination of acoustic telemetry and acceleration datalogger technology to gain fundamental insights into the fine-scale behaviour, habitat use, size of activity spaces, and residency of adult female bottlenose wedgefish (Rhynchobatus australiae) in the Ningaloo region of northwestern Australia. Acoustic tracking data over one year demonstrated that female bottlenose wedgefish continuously resided in a relatively small area of a productive coral reef lagoon. Acceleration data revealed that bottlenose wedgefish were nocturnal, with time of day having a greater influence on activity than tidal patterns. Bottlenose wedgefish also increased activity with seasonally increasing temperatures. We identified several discrete behavioural signatures in the acceleration data, inferred to correspond to chafing, settling/burying behaviour, foraging behaviour, and escape behaviour, based on their kinematics. Further observations are required to confirm these behaviours with certainty. Additionally, according to datalogger and acoustic data, tagged bottlenose wedgefish rarely inhabited areas greater than 2 m deep. Together, these first insights into behaviour and habitat use of adult female bottlenose wedgefish highlight the importance of nearshore habitats for this species and indicate that they may be highly resident to specific areas. Our findings provide important insight into the conservation of bottlenose wedgefish in northwestern Australia, including potential effectiveness of protected areas and interactions with specific anthropogenic threats such as shoreline development and recreational beach fishing.

Stomach eversion is common in sharks captured during fishing activities, however, records of subsequent retraction of the stomach once animals are released are rare and limited by the logistics of recording post-release behaviors in the wild. Here, we report stomach eversion and retraction by a tiger shark captured and tagged at Ningaloo Reef, Western Australia. Initial eversion occurred during capture, and retraction was recorded by video and tri-axial acceleration sensors approximately five minutes after release. The ability to retract the stomach without apparent ill effect is consistent with the documented resilience of tiger sharks to stressful capture events, but remains to be confirmed for other species.

Animal personalities are differences in behaviour among individuals of the same species that are consistent over time and contexts. The integration of animal personality into conservation actions is hampered by limited understanding of personality traits in non-model organisms. We estimated repeatabilities and correlations between behaviours in Nannoperca vittata (western pygmy perch), a threatened freshwater fish species endemic to south-western Australia, and, for comparative purposes, in Poecilia reticulata (guppy), a species frequently used in personality research. Each fish was measured four times for each of seven behavioural variables, presumed to reflect five underlying personality traits. Track length (TL) was used as a measure of activity; time spent in a risky zone (RZ) and time to emergence (ET) for boldness; latency to approach a novel object (LA) and time spent close to the object (TS) for exploration; time spent close to a mirror (CV) for sociability and number of attacks at the mirror (AT) for aggression. Four behavioural variables (TL, RZ, ET and CV) were significantly repeatable in N. vittata and also in P. reticulata. There was a lack of concordance in phenotypic and among-individual correlations between variables in both species, emphasising the importance of partitioning trait covariances to infer behavioural syndromes. Significant among-individual correlations were found between activity, boldness and sociability variables in N. vittata, consistent with a proactive-reactive personality axis, but not in P. reticulata. Personality variation should be considered in conservation actions for N. vittata, particularly with respect to unintended consequences of domestication selection in captive breeding and release.