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Integrated analysis of the vertical and horizontal movements of epipelagic fishes requires high-resolution data from tags that have been attached to animals for long periods. The recovery of a SPLASH tag deployed on a whale shark Rhincodon typus for 3 mo enabled access to archival data of horizontal and vertical movements of the shark that travelled 5380 km from Christmas Island to the Banda Sea. We examined water temperature and bathymetry to compare movements of the shark with key oceanographic features. Over 89 d, we identified 1931 dives and grouped these into 5 broad categories depending on dive shape. To investigate the potential for these dives to reflect behavioural thermoregulation, we used boosted regression trees to model the relationship between pre- and post-dive surface durations and dive characteristics. The movements of the shark were correlated with water temperatures, with the animal following frontal systems while remaining in a sea surface temperature (SST) range of 24-29°C. Across the continental shelf off north-western Australia, the shark mostly remained near the seafloor, likely avoiding very warm SSTs and strong currents at the surface. U- (foraging) and V- (searching) shaped dives accounted for ~78% of dives. Foraging dives during the day descended to 200-500 m and were preceded and followed by extended periods at the surface, whereas at night, the shark rarely dived below 200 m, likely foraging near the thermocline. Our results show how water temperatures influence the movement of this whale shark, with ‘basking’ at the surface during the day likely to gather environmental heat for thermoregulation, aiding to maintain body temperatures.

Monitoring the demographics and movement patterns of mobile marine species underpins appropriate management and conservation strategies. Photographic identification of whale sharks Rhincodon typus based on individual variations in spot patterns is a widely used technique for monitoring of populations, but relies on the untested assumptions that these variations in spot patterns are unique to each shark and can be reliably detected using photo-matching software. This study validated the accuracy of photo-identification technique by manually determining the number of photo-identified individuals showing mismatched genetic profiles created for the individuals using 12 microsatellite markers. Results from 154 photographic and genetic identifications of whale sharks were 100% concordant, showing the uniqueness of spot patterns to each shark and high accuracy of the photo-identification technique. Based on these techniques, we observed an annual resighting rate of approximately 10% at Ningaloo Reef, Western Australia, between 2016 and 2018, showing evidence that variations in spot patterns did not change over a time scale of years. Our study shows that the photographic identification technique provides a reliable means to recognise individuals and monitor whale sharks through time.

Anthropogenic impacts at isolated and inaccessible reefs are often minimal, offering rare opportunities to observe fish assemblages in a relatively undisturbed state. The remote Rowley Shoals are regarded as one of the healthiest reef systems in the Indian Ocean with demonstrated resilience to natural disturbance, no permanent human population nearby, low visitation rates, and large protected areas where fishing prohibitions are enforced. We used baited remote underwater video systems (BRUVS) to quantify fish assemblages and the relative abundance of regionally fished species within the lagoon, on the slope and in the mesophotic habitat at the Rowley Shoals at three times spanning 14 years and compared abundances of regionally fished species and the length distributions of predatory species to other isolated reefs in the northeast Indian Ocean. Fish assemblage composition and the relative abundance of regionally fished species were remarkably stable through time. We recorded high abundances of regionally fished species relative to other isolated reefs, including globally threatened humphead Maori wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum). Length distributions of fish differed among habitats at the Rowley Shoals, suggesting differences in ontogenetic shifts among species. The Cocos (Keeling) Islands typically had larger‐bodied predatory species than at the Rowley Shoals. Differences in geomorphology, lagoonal habitats, and fishing history likely contribute to the differences among remote reefs. Rowley Shoals is a rare example of a reef system demonstrating ecological stability in reef fish assemblages during a time of unprecedented degradation of coral reefs., Fish assemblage composition and the relative abundance of regionally fished species were remarkably stable through time at the Rowley Shoals. We recorded high abundances of regionally fished species relative to other isolated reefs, including globally threatened humphead Maori wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum).

Identification of latitudinal trends in growth and maximum ages provides important insights into the vulnerability of coral reef fishes to human exploitation. Here, we sampled three species of unharvested tropical snappers from 4 locations along the tropical Western Australian coast and from the Chagos Archipelago in the central Indian Ocean. Interpretation of sectioned sagittal otoliths identified 2 species as the longest-lived tropical reef-associated fishes recorded to date, with a combined eleven specimens aged > 60 yrs, a single Lutjanus bohar aged 79 yrs and a single Macolor macularis aged 81 yrs (both from Rowley Shoals, Western Australia). These maximum ages are two decades greater than previous estimates of maximum age for reef fishes. Lifetimes of such long durations confirm the low rates of natural mortality for these species, their associated low production potential, and the need for effective systems of governance to enable sustainable harvests across the distributions of these species.

[Extract:] In their study, Clark et al. suggest that previous studies on the effects of elevated levels of CO2 on the behaviour of coral reef fishes are not repeatable and that ocean acidification does not impair the behaviour of coral reef fishes, even though six significant behavioural effects were detected in their study, each of which was dismissed for a different reason. They then compare the means and variances of six previous ocean acidification studies in fish with a data distribution that is derived from a multi-species compilation of their own data to conclude that the results of previous studies are statistically improbable. However, Clark et al. did not closely repeat previous studies, as they did not replicate key species, used different life stages and ecological histories and changed methods in important ways that reduce the likelihood of detecting the effects of ocean acidification.

Predators can exert strong ecological effects on their prey either via consumption or by altering their behaviour and morphology. In marine systems, predators and their prey co-occur in a three-dimensional environment, but to date predator-prey studies have largely focussed on behaviours of prey on horizontal (distance from shelter) rather than vertical (height in water column) axes. We used life-size shape-models of a blacktip reef shark Carcharhinus melanopterus (threatening shape-model), a juvenile coral trout Plectropomus leopardus (non-threatening shape-model) and a shape-control to examine the impact of perceived instantaneous (measured by time to first feeding) versus sustained (measured by time to consume the entire bait) predation threats on the feeding behaviour and three-dimensional use of space by mesopredatory reef fishes in a coral reef environment. We found that mesopredatory fishes such as red snapper Lutjanus bohar and spangled emperor Lethrinus nebulosus took longer to begin feeding and to consume predation assays (fish baits) at greater distances from the shelter of a patch reef across both horizontal and vertical axes and that this phenomenon was stronger in the vertical axis than the horizontal. The presence of a life-size shape-model of a shark, which we used to increase the perception of predator threat, magnified the instantaneous effect compared to non-threatening models, but not the sustained effect. We found no evidence for a difference in the level of predation risk posed by the shape-model of the juvenile coral trout (a non-threatening reef fish) and a negative control (no shape-model). Our study suggests that mesopredators modify their behaviours in response to the perceived risk of predation across both horizontal and vertical axes away from shelter, and that this response is most severe on the vertical axis, potentially limiting daytime foraging behaviour to a hemisphere around shelter sites.

Population genetic data can provide valuable information on the demography of a species. For rare and elusive marine megafauna, samples for generating the data are traditionally obtained from tissue biopsies, which can be logistically difficult and expensive to collect and require invasive sampling techniques. Analysis of environmental DNA (eDNA) offers an alternative, minimally invasive approach to provide important genetic information. Although eDNA approaches have been studied extensively for species detection and biodiversity monitoring in metabarcoding studies, the potential for the technique to address population-level questions remains largely unexplored. Here, we applied “eDNA haplotyping” to obtain estimates of the intraspecific genetic diversity of a whale shark (Rhincodon typus) aggregation at Ningaloo reef, Australia. Over 2 weeks, we collected seawater samples directly behind individual sharks prior to taking a tissue biopsy sample from the same animal. Our data showed a 100% match between mtDNA sequences recovered in the eDNA and tissue sample for all 28 individuals sampled. In the seawater samples, >97% of all reads were assigned to six dominant haplotypes, and a clear dominant signal (~99% of sample reads) was recovered in each sample. Our study demonstrates accurate individual-level haplotyping from seawater eDNA. When DNA from one individual clearly dominates each eDNA sample, it provides many of the same opportunities for population genetic analyses as a tissue sample, potentially removing the need for tissue sampling. Our results show that eDNA approaches for population-level analyses have the potential to supply critical demographic data for the conservation and management of marine megafauna.

Biological feedbacks generated through patterns of disturbance are vital for sustaining ecosystem states. Recent ocean warming and thermal anomalies have caused pantropical episodes of coral bleaching, which has led to widespread coral mortality and a range of subsequent effects on coral reef communities. Although the response of many reef-associated fishes to major disturbance events on coral reefs is negative (e.g., reduced abundance and condition), parrotfishes show strong feedbacks after disturbance to living reef structure manifesting as increases in abundance. However, the mechanisms underlying this response are poorly understood. Using biochronological reconstructions of annual otolith (ear stone) growth from two ocean basins, we tested whether parrotfish growth was enhanced following bleaching-related coral mortality, thus providing an organismal mechanism for demographic changes in populations. Both major feeding guilds of parrotfishes (scrapers and excavators) exhibited enhanced growth of individuals after bleaching that was decoupled from expected thermal performance, a pattern that was not evident in other reef fish taxa from the same environment. These results provide evidence for a more nuanced ecological feedback system-one where disturbance plays a key role in mediating parrotfish-benthos interactions. By influencing the biology of assemblages, disturbance can thereby stimulate change in parrotfish grazing intensity and ultimately reef geomorphology over time. This feedback cycle operated historically at within-reef scales; however, our results demonstrate that the scale, magnitude, and severity of recent thermal events are entraining the biological responses of disparate communities to respond in synchrony. This may fundamentally alter feedbacks in the relationships between parrotfishes and reef systems.

Provisioning of whale sharks (Rhincodon typus) for tourism at Oslob in the Philippines is a controversial issue. Recent studies that claim negative impacts of this industry on the ecology of whale sharks are characterised by a lack of baselines, limited methodological approaches and poor interpretation of results. They do not provide robust evidence for management or for advocacy that seeks to prevent provisioning. Furthermore, these studies cannot be used to draw conclusions about the ethics of tourists visiting Oslob or the motivations of the local people running the tourism operation.

Significance Seismic surveys are used to locate deposits of oil and gas in seabeds throughout the world’s oceans. There are conflicting views on the impact of these surveys on fish fauna and whether they harm commercial catches. To resolve this issue, we conducted an experimental seismic survey and monitored the composition, abundance, behavior, and movement of an assemblage of commercially important demersal fishes on a shelf habitat using acoustic telemetry and underwater video. We found that the seismic survey did not alter fish abundance or behavior in multiple before-after-control-impact and dose–response experimental frameworks. Our work may allay some of the concerns of stakeholders about the negative impacts of seismic surveys on demersal fishes in tropical shelf environments., Seismic surveys are used to locate oil and gas reserves below the seabed and can be a major source of noise in marine environments. Their effects on commercial fisheries are a subject of debate, with experimental studies often producing results that are difficult to interpret. We overcame these issues in a large-scale experiment that quantified the impacts of exposure to a commercial seismic source on an assemblage of tropical demersal fishes targeted by commercial fisheries on the North West Shelf of Western Australia. We show that there were no short-term (days) or long-term (months) effects of exposure on the composition, abundance, size structure, behavior, or movement of this fauna. These multiple lines of evidence suggest that seismic surveys have little impact on demersal fishes in this environment.

Whale sharks off the western coast of India have suffered high levels of fishing pressure in the past, and today continue to be caught in small-scale fisheries as by-catch. Additionally, coastlines in this region host very large and growing human populations that are undergoing rapid development. This exacerbates ongoing anthropogenic threats to this species such as pollution, habitat loss, and ship traffic. For these reasons, there is an urgent need for data on movement patterns of whale sharks in this region of the Indian Ocean. Here, we address this issue by providing the first data on the horizontal movements of whale sharks tagged in the northern Arabian Sea off the western coast of the Indian state of Gujarat. From 2011 to 2017, eight individuals, ranging from 5.4 to 8 m were tagged and monitored using satellite telemetry. Tag retention varied from 1 to 137 days, with the sharks traveling distances of 34 – ∼2,230 km. Six of the eight individuals remained close to their tagging locations, although two sharks displayed wide ranging movements into the Arabian Sea, following frontal zones between water masses of different sea surface temperatures. We explore the relationship between the movement patterns of these whale sharks and the physical and biological processes of the region.

By improving resource quality, cross-ecosystem nutrient subsidies may boost demographic rates of consumers in recipient ecosystems, which in turn can affect population and community dynamics. However, empirical studies on how nutrient subsidies simultaneously affect multiple demographic rates are lacking, in part because humans have disrupted the majority of these natural flows. Here, we compare the demographics of a sex-changing parrotfish (Chlorurus sordidus) between reefs where cross-ecosystem nutrients provided by seabirds are available versus nearby reefs where invasive, predatory rats have removed seabird populations. For this functionally important species, we found evidence for a trade-off between investing in growth and fecundity, with parrotfish around rat-free islands with many seabirds exhibiting 35% faster growth, but 21% lower size-based fecundity, than those around rat-infested islands with few seabirds. Although there were no concurrent differences in population-level density or biomass, overall mean body size was 16% larger around rat-free islands. Because the functional significance of parrotfish as grazers and bioeroders increases non-linearly with size, the increased growth rates and body sizes around rat-free islands likely contributes to higher ecosystem function on coral reefs that receive natural nutrient subsidies. More broadly, these results demonstrate additional benefits, and potential trade-offs, of restoring natural nutrient pathways for recipient ecosystems.

Predation on parasites is an important ecological process, but few experimental studies have examined the long-term impacts on the prey. Cleaner fish prey upon large numbers and selectively feed on the larger individuals of the ectoparasitic stage of gnathiid isopods. Removal of cleaner fish Labroides dimidiatus for 1.5–12.5 years negatively affects coral reef fishes, but the mechanism is unclear. A reduction in local parasite populations or the size of individual parasites would benefit all susceptible fishes. We tested whether cleaner presence reduces local gnathiid populations using 18 patch-reefs distributed between two sites (both at Lizard Island, Great Barrier Reef) which were maintained cleaner-free or undisturbed for 12 years. Using emergence traps (1 m2), free-living gnathiid stages were sampled before and after cleaner fish were removed during the day and night, up to 11 times over the course of the experiment. There were effects of the removal in the predicted direction, driven largely by the response at one site over the other involving 200% more gnathiids, but manifested only in the daytime sampling after 4 months. There was also a main effect (36%) for the shared sample dates at both sites after 12 years. Gnathiid size occasionally differed with cleaner presence, but in no consistent way over time. Contrary to our predictions, changes in free-living gnathiid population numbers and their size structure rarely reflected the changes in fish populations and individuals observed on cleaner-free reefs. Therefore, evidence that this predator alone regulates gnathiids remains limited, suggesting other contributing processes are involved.

Large epipelagic fishes (> 30 kg maximum size) are known to display a variety of patterns of vertical movement. Although advances in the affordability and sophistication of electronic tags now allows researchers to routinely document these patterns, there is no standardised approach to classify these behaviours and investigate their physical and biological drivers. This paper reviews the existing knowledge of the vertical movements of large, epipelagic fishes and the evidence for the underlying factors that structure this behaviour. The review focuses on behaviours occurring at a range of temporal scales, from seconds to years. We propose that patterns of vertical movement in gill-breathing animals of the epipelagic are best characterised by the need to move continuously in a three-dimensional environment while optimising food encounter and energy expenditure, avoiding predators, searching for mates and remaining within the limits imposed by the physical environment on their physiology (notably water temperature and oxygen). Modern biologging technologies that record both the internal (body temperature, heart rate) and external physical environment coupled with direct recording of behaviour from tri-axial sensors and animal-borne cameras offer a new approach to the analysis of drivers of vertical movement. Ultimately, this can provide insights into the evolution of the behaviour and morphology of these animals.

COVID-19 restrictions have led to an unprecedented global hiatus in anthropogenic activities, providing a unique opportunity to assess human impact on biological systems. Here, we describe how a national network of acoustic tracking receivers can be leveraged to assess the effects of human activity on animal movement and space use during such global disruptions. We outline variation in restrictions on human activity across Australian states and describe four mechanisms affecting human interactions with the marine environment: 1) reduction in economy and trade changing shipping traffic; 2) changes in export markets affecting commercial fisheries; 3) alterations in recreational activities; and 4) decline in tourism. We develop a roadmap for the analysis of acoustic tracking data across various scales using Australia's national Integrated Marine Observing System (IMOS) Animal Tracking Facility as a case study. We illustrate the benefit of sustained observing systems and monitoring programs by assessing how a 51-day break in white shark (Carcharodon carcharias) cage-diving tourism due to COVID-19 restrictions affected the behaviour and space use of two resident species. This cessation of tourism activities represents the longest break since cage-diving vessels started day trips in this area in 2007. Long-term monitoring of the local environment reveals that the activity space of yellowtail kingfish (Seriola lalandi) was reduced when cage-diving boats were absent compared to periods following standard tourism operations. However, white shark residency and movements were not affected. Our roadmap is globally applicable and will assist researchers in designing studies to assess how anthropogenic activities can impact animal movement and distributions during regional, short-term through to major, unexpected disruptions like the COVID-19 pandemic.

Given the recent trend towards establishing very large marine protected areas (MPAs) and the high potential of these to contribute to global conservation targets, we review outcomes of the last decade of marine conservation research in the British Indian Ocean Territory (BIOT), one of the largest MPAs in the world. The BIOT MPA consists of the atolls of the Chagos Archipelago, interspersed with and surrounded by deep oceanic waters. Islands around the atoll rims serve as nesting grounds for sea birds. Extensive and diverse shallow and mesophotic reef habitats provide essential habitat and feeding grounds for all marine life, and the absence of local human impacts may improve recovery after coral bleaching events. Census data have shown recent increases in the abundance of sea turtles, high numbers of nesting seabirds and high fish abundance, at least some of which is linked to the lack of recent harvesting. For example, across the archipelago the annual number of green turtle clutches (Chelonia mydas) is ~ 20,500 and increasing and the number of seabirds is ~ 1 million. Animal tracking studies have shown that some taxa breed and/or forage consistently within the MPA (e.g. some reef fishes, elasmobranchs and seabirds), suggesting the MPA has the potential to provide long-term protection. In contrast, post-nesting green turtles travel up to 4000 km to distant foraging sites, so the protected beaches in the Chagos Archipelago provide a nesting sanctuary for individuals that forage across an ocean basin and several geopolitical borders. Surveys using divers and underwater video systems show high habitat diversity and abundant marine life on all trophic levels. For example, coral cover can be as high as 40–50%. Ecological studies are shedding light on how remote ecosystems function, connect to each other and respond to climate-driven stressors compared to other locations that are more locally impacted. However, important threats to this MPA have been identified, particularly global heating events, and Illegal, Unreported and Unregulated (IUU) fishing activity, which considerably impact both reef and pelagic fishes.

Made available in DSpace on 2021-06-25T12:19:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-24 Australian Government's National Environmental Science Program Australian Research Data Commons GorgonBarrow Island Gorgon Barrow Island Net Conservation Benefits Fund Baited remote underwater stereo-video systems (stereo-BRUVs) are a popular tool to sample demersal fish assemblages and gather data on their relative abundance and body size structure in a robust, cost-effective and non-invasive manner. Given the rapid uptake of the method, subtle differences have emerged in the way stereo-BRUVs are deployed and how the resulting imagery is annotated. These disparities limit the interoperability of datasets obtained across studies, preventing broadscale insights into the dynamics of ecological systems. We provide the first globally accepted guide for using stereo-BRUVs to survey demersal fish assemblages and associated benthic habitats. Information on stereo-BRUVs design, camera settings, field operations and image annotation are outlined. Additionally, we provide links to protocols for data validation, archiving and sharing. Globally, the use of stereo-BRUVs is spreading rapidly. We provide a standardized protocol that will reduce methodological variation among researchers and encourage the use of Findable, Accessible, Interoperable and Reusable workflows to increase the ability to synthesize global datasets and answer a broad suite of ecological questions. Univ Western Australia, UWA Oceans Inst, Perth, WA, Australia Univ Western Australia, Sch Biol Sci, Perth, WA, Australia Dept Biodivers Conservat & Attract, Marine Sci Program, Biodivers & Conservat Sci, Kensington, WA, Australia Curtin Univ, Sch Mol & Life Sci, Perth, WA, Australia Univ Tasmania, Inst Marine & Antarctic Studies, Hobart, Tas, Australia Silliman Univ, Angelo King Ctr Res & Environm Management, Dumaguete, Philippines NOAA Inouye Reg Ctr, NOAA Fisheries, Pacific Isl Fisheries Sci Ctr, Sci Operat Div, Honolulu, HI USA Univ Hawaii Manoa, Joint Inst Marine & Atmospher Res, Honolulu, HI 96822 USA South African Inst Aquat Biodivers, Grahamstown, South Africa Rhodes Univ, Dept Zool & Entomol, Grahamstown, South Africa Univ St Andrews, Ctr Res Ecol & Environm Modelling, Sch Math & Stat, St Andrews, Fife, Scotland Indian Ocean Marine Res Ctr, Australian Inst Marine Sci, Perth, WA, Australia Australian Inst Marine Sci, Townsville, Qld, Australia Govt Western Australia, Western Australian Fisheries & Marine Res Labs, Dept Primary Ind & Reg Dev, North Beach, WA, Australia NSW Dept Primary Ind, Fisheries Res, Taylors Beach, NSW, Australia Dept Environm & Water, Marine Sci Program, Sci & Corp Serv Div, Adelaide, SA, Australia Flinders Univ S Australia, Southern Shark Ecol Grp, Coll Sci & Engn, Bedford Pk, SA, Australia Deakin Univ, Sch Life & Environm Sci, Ctr Integrat Ecol, Warrnambool, Vic, Australia NSW Dept Primary Ind, Fisheries Res, Huskisson, NSW, Australia Coral Reef Res Fdn, Koror, Palau NSW Dept Primary Ind, Fisheries Res, Coffs Harbour, NSW, Australia Ctr Environm Fisheries & Aquaculture Sci, Lowestoft, Suffolk, England Sao Paulo State Univ, Elasmobranch Res Lab, Inst Biosci, Sao Vicente, SP, Brazil Massey Univ, Sch Nat & Computat Sci, Auckland, New Zealand Sao Paulo State Univ, Elasmobranch Res Lab, Inst Biosci, Sao Vicente, SP, Brazil

Age and growth data are central to management or conservation strategies for any species. Circumstantial evidence suggests that male whale sharks (Rhincodon typus) grow to asymptotic sizes much smaller than those predicted by age and growth studies and consequently, there may be sex-specific size and growth patterns in the species. We tested this hypothesis by using stereo-video and photo-identification studies to estimate the growth rates of 54 whale sharks that were resighted over a period of up to a decade at Ningaloo Reef. We found that male growth patterns were consistent with an average asymptotic total length (TL) of approximately 8–9 m, a size similar to direct observations of size at maturity at aggregation sites world-wide and much smaller than the sizes predicted by earlier modeling studies. Females were predicted to grow to an average asymptotic length of around 14.5 m. Males had growth coefficients of K = 0.088 year–1, whereas limited resighting data suggested a growth coefficient of K = 0.035 year–1 for females. Other data including re-sightings of an individual male over two decades, records of sex-specific maximum sizes of individuals captured in fisheries and data from juveniles growing in aquaria were also consistent with the suggestion of sex-specific growth profiles for the species. We argue that selection for sex-specific growth patterns could explain many of the otherwise enigmatic patterns in the ecology of this species including the tendency of the species to form aggregations of juvenile males in coastal waters.

Publisher's version (útgefin grein), Conservation and management strategies for endangered and threatened species require accurate estimates of demographic parameters such as age and growth. The whale shark, Rhincodon typus, is the largest fish in the world and is highly valued in the eco-tourism sector. Despite conservation concerns and advances in our understanding of their life history, basic demographic parameters for growth, longevity and mortality are of questionable accuracy; previous growth studies could not agree whether the vertebral growth bands were formed annually or biannually. Here, we provide the first validation of the annual formation of growth bands within the vertebrae of the whale shark using bomb radiocarbon assays. Ages of up to 50 years were estimated from sectioned vertebrae of sharks collected in Taiwan and Pakistan. There was no cessation of the formation of growth bands in the vertebrae of older sharks and our study provides the oldest observed longevity for this species. Initial estimates of growth (k = 0.01–0.12) and natural mortality rates (M = 0.09–0.14) are consistent with those expected of long-lived sharks, which highlights their sensitivity to fishing pressure and conservation concerns., This work was supported by the Fisheries and Oceans Canada, US National Science Foundation Grant OCE-9985884, and the University of Iceland. Travel funding was provided by the Australian Institute of Marine Science.

There is limited evidence on the rate at which the shark populations of coral reefs can rebound from over-exploitation, the baselines that might signify when recovery has occurred and the role of no-take Marine Protected Areas (MPA) in aiding this process. We surveyed shark assemblages at Ashmore Reef in Western Australia using baited remote underwater video stations in 2004 prior to enforcement of MPA status and then again in 2016 after eight years of strict enforcement. We found an increase in the relative mean abundance of Carcharhinus amblyrhynchos from 0.16 ± 0.06 individuals h−1 in 2004 to 0.74 ± 0.11 individuals h−1 in 2016, a change that was also accompanied by a shift in the assemblage of sharks to greater proportions of apex species (from 7.1% to 11.9%) and reef sharks (from 28.6% to 57.6%), and a decrease in the proportional abundance of lower trophic level species (from 64.3% to 30.5%). Abundances and trophic assemblage of sharks at Ashmore Reef in 2004 resembled those of the Scott Reefs, where targeted fishing for sharks still occurs, whereas in 2016, abundances and trophic structures had recovered to resemble those of the Rowley Shoals, a reef system that has been a strictly enforced MPA for over 25 years. The shift in abundance and community structure coincident with strict enforcement of the MPA at Ashmore Reef has occurred at a rate greater than predicted by demographic models, implying the action of compensatory processes in recovery. Our study shows that shark communities can recover rapidly after exploitation in a well-managed no-take MPA.

Female octopuses are known to store sperm from multiple males they encounter throughout a breeding season, before laying a single clutch with mixed paternity. Although octopuses display a broad range of precopulatory behaviours, and both sperm competition and cryptic female choice have been hypothesized to occur, the current understanding of how these processes influence resulting paternity remains limited. This study aimed to identify behavioural factors associated with paternity patterns and the capacity of females to bias paternity postcopulation to specific males in the southern blue-ringed octopus, Hapalochlaena maculosa. Genetic markers and controlled, sequential, laboratory pairings of genotyped individuals were used to examine paternity patterns and compare them to relative signatures of male sperm remaining in female oviducal glands after egg laying. Multiple paternity was discovered in all 12 laboratory-reared clutches. There was no indication that the relative time spent in copulation affected the resulting paternity. Males that waited for females to terminate the copulation had greater paternity when they were the first candidate male, but this was not the case among second candidate males. The relative quantities of candidate male alleles detected in female oviducal glands after egg laying were consistent with relative paternity of the candidate males in all but three cases. In one of these, sibship analysis revealed that the male that obtained less paternity than expected was in fact the female's full-sibling brother. Although this study found no evidence for female postcopulatory selection of male sperm, anecdotal evidence suggests that female H. maculosa might benefit from polyandry if chemical processes can favour clutch fertilization by unrelated males. Future studies, investigating paternity bias among genotyped males of varying, but known relatedness to the female, might help to validate this pattern.

The southern blue‐ringed octopus, Hapalochlaena maculosa (Hoyle, 1883) lacks a planktonic dispersal phase, yet ranges across Australia's southern coastline. This species’ brief and holobenthic life history suggests gene flow might be limited, leaving distant populations prone to strong genetic divergence. This study used 17,523 genome‐wide SNP loci to investigate genetic structuring and local adaptation patterns of H. maculosa among eight sampling sites along its reported range. Within sites, interrelatedness was very high, consistent with the limited dispersal of this taxon. However, inbreeding coefficients were proportionally lower among sites where substructuring was not detected, suggesting H. maculosa might possess a mechanism for inbreeding avoidance. Genetic divergence was extremely high among all sites, with the greatest divergence observed between both ends of the distribution, Fremantle, WA, and Stanley, TAS. Genetic distances closely followed an isolation by geographic distance pattern. Outlier analyses revealed distinct selection signatures at all sites, with the strongest divergence reported between Fremantle and the other Western Australian sites. Phylogenetic reconstructions using the described sister taxon H. fasciata (Hoyle, 1886) further supported that the genetic divergence between distal H. maculosa sites in this study was equivalent to that of between established heterospecifics within this genus. However, it is advocated that taxonomic delineations within this species should be made with caution. These data indicate that H. maculosa forms a clinal species pattern across its geographic range, with gene flow present through allele sharing between adjacent populations. Morphological investigations are recommended for a robust resolution of the taxonomic identity and ecotype boundaries of this species.

Mobile species often aggregate at predictable places and times to ensure that individuals find mates and breed in suitable habitats. Sea turtles demonstrate this life history trait, which can make these species highly susceptible to population declines if nesting habitats are lost or degraded. Conservation management thus requires knowledge of where and when turtles nest and changes in abundance in these habitats through time. Here, we compiled new and published data and used a novel analysis to describe seasonality, annual abundance and spatial distribution of nesting green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles in data-deficient populations that inhabit the Red Sea. Major new rookeries were identified for green turtles at Jazirat 1 Mashabah (113 and 179 nesting females in 2018 and 2019) and for hawksbill turtles at Jazirat Al Waqqadi (79 nesting females in 2018), both of which are located on nearshore islands of the Kingdom of Saudi Arabia in an area subject to industrial, residential and ecotourism developments. An upward trend in annual abundance of nesting sea turtles was estimated at some sites including Ras Al Baridi (Saudi Arabia), a major rookery of green turtles in the Red Sea, where the annual numbers increased from 14–110 individuals in 1982–1995 to 178 and 330 individuals in 2018 and 2019. This integrative work provides the most up-to-date, comprehensive information on nesting sea turtles in the Red Sea and documents a critical baseline for sea turtle conservation and future management effort.

Mutualisms are pivotal in shaping ecological communities. Iconic images of cleaner fish entering the mouths of predatory fish clients to remove ectoparasites epitomize their mutual benefit. Experimental manipulations of cleaner wrasse reveal declines in fish size and growth, and population abundance and diversity of client fishes in the absence of cleaner wrasse. Fishes grow more slowly and are less abundant and diverse on reefs without cleaner wrasse, both for larger species that are regularly cleaned and have high ectoparasite loads (“attractive species”), and for those smaller species that are rarely cleaned and are rarely infested with parasites (“unattractive species”). We therefore considered whether these previously observed declines in individual and population parameters on reefs without cleaners were related to increased ectoparasite infestation using an attractive species (Hemigymnus melapterus, Labridae) and an unattractive species (Pomacentrus amboinensis, Pomacentridae). Traps with these fish as a form of bait were deployed to sample blood-sucking gnathiid ectoparasites (Gnathiidae: Isopoda) on reefs from which cleaners (Labroides dimidiatus, Labridae) have been removed for 13 yr. Cleaner fish could not enter traps to access the clients/hosts, but gnathiids could enter the traps to infest hosts; thus, this method sampled the indirect effect of cleaners on gnathiid infestation of fish. Infestation was higher on reefs without cleaners than on those with them. The effect was only detected during the daytime when cleaners are active and only on the attractive species (H. melapterus). Thus, cleaner presence indirectly reduced fish exposure to parasites in a species that is highly susceptible to parasites, but not in one that is rarely infested with parasites. This suggests that cleaner presence indirectly reduces exposure of a common fish species to harmful parasites, which may explain some observed benefits in fishes at this location.

Anthropogenic activities such as land-use change, pollution and fishing impact the trophic structure of coral reef fishes, which can influence ecosystem health and function. Although these impacts may be ubiquitous, they are not consistent across the tropical Pacific Ocean. Using an extensive database of fish biomass sampled using underwater visual transects on coral reefs, we modelled the impact of human activities on food webs at Pacific-wide and regional (1,000s-10,000s km) scales. We found significantly lower biomass of sharks and carnivores, where there were higher densities of human populations (hereafter referred to as human activity); however, these patterns were not spatially consistent as there were significant differences in the trophic structures of fishes among biogeographic regions. Additionally, we found significant changes in the benthic structure of reef environments, notably a decline in coral cover where there was more human activity. Direct human impacts were the strongest in the upper part of the food web, where we found that in a majority of the Pacific, the biomass of reef sharks and carnivores were significantly and negatively associated with human activity. Finally, although human-induced stressors varied in strength and significance throughout the coral reef food web across the Pacific, socioeconomic variables explained more variation in reef fish trophic structure than habitat variables in a majority of the biogeographic regions. Notably, economic development (measured as GDP per capita) did not guarantee healthy reef ecosystems (high coral cover and greater fish biomass). Our results indicate that human activities are significantly shaping patterns of trophic structure of reef fishes in a spatially nonuniform manner across the Pacific Ocean, by altering processes that organize communities in both "top-down" (fishing of predators) and "bottom-up" (degradation of benthic communities) contexts.

Tiger sharks were sampled off the western (Ningaloo Reef, Shark Bay) and eastern (the Great Barrier Reef; GBR, Queensland and New South Wales; NSW) coastlines of Australia. Multiple tissues were collected from each shark to investigate the effects of location, size and sex of sharks on δ13C and δ15N stable isotopes among these locations. Isotopic composition of sharks sampled in reef and seagrass habitats (Shark Bay, GBR) reflected seagrass-based food-webs, whereas at Ningaloo Reef analysis revealed a dietary transition between pelagic and seagrass food-webs. In temperate habitats off southern Queensland and NSW coasts, shark diets relied on pelagic food-webs. Tiger sharks occupied roles at the top of food-webs at Shark Bay and on the GBR, but not at Ningaloo Reef or off the coast of NSW. Composition of δ13C in tissues was influenced by body size and sex of sharks, in addition to residency and diet stability. This variability in stable isotopic composition of tissues is likely to be a result of adaptive foraging strategies that allow these sharks to exploit multiple shelf and offshore habitats. The trophic role of tiger sharks is therefore both context- and habitat-dependent, consistent with a generalist, opportunistic diet at the population level.

Most studies investigating the effects of anthropogenic environmental stressors do so in conditions that are often optimal for their test subjects, ignoring natural stressors such as competition or predation. As such, the quantitative results from such studies may often underestimate the lethality of certain toxic compounds. A well-known example of this concept is illustrated by the marked increase in the lethality of pesticides when larval amphibians are concurrently exposed to the odor of potential predators. Here, we investigated the interaction between background levels of environmental predation risk (high vs. low) and ocean acidification (ambient vs. elevated CO2) in 2 × 2 design. Wild-caught juvenile damselfish, Pomacentrus amboinensis, were exposed in the laboratory to the different risk and CO2 conditions for 4 days and released onto coral reef patches. Using a well-established field assay, we monitored the in situ behavior and mortality of the damselfish for 2 days. We predicted that juvenile fish exposed to elevated CO2 and high-risk conditions would display more severe behavioral impairments and increased mortality compared to fish exposed to elevated CO2 maintained under low-risk conditions. As expected, elevated CO2 exposure led to impaired antipredator responses and increased mortality in low-risk fish compared to ambient CO2 controls. However, we failed to find an effect of elevated CO2 on the behavior and survival of the high-risk fish. We hypothesized that the results may stem from either a behavioral compensation or a physiological response to high risk. Our results provide insights into the interactive nature of environmental and natural stressors and advance our understanding of the predicted effect of ocean acidification on aquatic ecosystems.

Shark-diving is part of a rapidly growing industry focused on marine wildlife tourism. Our study aimed to provide an estimate of the economic value of shark-diving tourism across Australia by comprehensively surveying the whale shark (Rhincodon typus), white shark (Carcharodon carcharias), grey nurse shark (Carcharias taurus), and reef shark (mostly Carcharhinus amblyrhynchos and Triaenodon obesus) diving industries using a standardised approach. A socio-economic survey targeted tourist divers between March 2013 and June 2014 and collected information on expenditures related to diving, accommodation, transport, living costs, and other related activities during divers’ trips. A total of 711 tourist surveys were completed across the four industries, with the total annual direct expenditure by shark divers in Australia estimated conservatively at $25.5 M. Additional expenditure provided by the white-shark and whale-shark-diving industries totalled $8.1 and $12.5 M for the Port Lincoln and Ningaloo Reef regions respectively. International tourists diving with white sharks also expended another $0.9 M in airfares and other activities while in Australia. These additional revenues show that the economic value of this type of tourism do not flow solely to the industry, but are also spread across the region where it is hosted. This highlights the need to ensure a sustainable dive-tourism industry through adequate management of both shark-diver interactions and biological management of the species on which it is based. Our study also provides standardised estimates which allow for future comparison of the scale of other wildlife tourism industries (not limited to sharks) within or among countries.

We thank the University of Western Australia (UWA), Perth, which partly funded this research via an International Postgraduate Research Scholarship and the Australian Institute of Marine Science. We also thank the Department of Fisheries, the Department of Parks and Wildlife (DPaW) and the Department of Sustainability, Environment, Water, Population and Communities for arranging permits to conduct research at the Scott Reefs and the Rowley Shoals. Thank you also to the crew on board the RV 'Solander'. This research was permitted under UWA Ethics Approvals: RA3/100/1279, RA3/100/1172.

Fishing and habitat degradation have increased the extinction risk of sharks, and conservation strategies recognize that survival of juveniles is critical for the effective management of shark populations. Despite the rapid expansion of marine protected areas (MPAs) globally, the paucity of shark-monitoring data on large scales (100s–1000s km) means that the effectiveness of MPAs in halting shark declines remains unclear. Using data collected by baited remote underwater video systems (BRUVS) in northwestern Australia, we developed generalized linear models to elucidate the ecological drivers of the occurrence of juvenile shark habitat. We assessed occurrence patterns at the order and species levels. We included all juvenile sharks sampled and the 3 most abundant species sampled separately (grey reef [Carcharhinus amblyrhynchos], sandbar [Carcharhinus plumbeus], and whitetip reef [Triaenodon obesus]. We predicted the occurrence of juvenile sharks across 490,515 km2 of coastal waters and quantified the representation of highly suitable habitats within MPAs. Our species-level models had higher accuracy (ĸ ≥ 0.69) and deviance explained (≥ 48 %) than our order-level model (ĸ = 0.36 and deviance explained of 10 %). Maps of predicted occurrence revealed different species-specific patterns of highly suitable habitat. These differences likely reflect different physiological or resource requirements between individual species and validate concerns over the utility of conservation targets based on aggregate species groups as opposed to a species-focused approach. Highly suitable habitats were poorly represented in MPAs with the most restrictions on extractive activities. This spatial mismatch possibly indicates a lack of explicit conservation targets and information on species distribution during the planning process. The nonextractive BRUVS provided a useful platform for building the suitability models across large scales to assist conservation planning across multiple maritime jurisdictions, and our approach provides a simple for method for testing the effectiveness of MPAs. This article is protected by copyright. All rights reserved

Chemoreception cues potentially influence intraspecific interactions of cephalopods, including mate choice. However, at present there is limited empirical evidence demonstrating whether cephalopods can use olfaction to identify the sex or identity of conspecifics. This study examined the responses of the southern blueringed octopus, Hapalochlaena maculosa (Hoyle, 1883), to conspecific odours during controlled laboratory trials. The ventilation rates in aquaria of 25 wild-sourced animals were measured during four treatments: baseline, sea water, sea water containing male conspecific odour and sea water containing female conspecific odour. When used as 'receivers' in trials, female H. maculosa significantly increased their ventilation rates in response to male odours, but not to female odours. However, female response decreased significantly with the receiver's size during female-odour treatments. The ventilation rates of male H. maculosa were statistically similar in all treatments. However, their ventilation rates showed a significant progressive increase over the observation period during male and female-odour treatments. Eighteen of these animals (nine females and nine males) were used in focal-animal trials 1 week after odour-cue experiments. Of these individuals, females were significantly more receptive to copulation attempts, and spent significantly more time per day in copulation, with males whose odours had elicited a weaker ventilation response in prior trials. These results suggest that female H. maculosa can use chemosensory cues to discriminate the sex, and possibly identity, of conspecifics and that this information might influence their mate choice. However, the mechanisms underlying these responses and subsequent copulatory access to females by males remain unknown.

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

Variation in life-history characteristics is evident within and across animal populations. Such variation is mediated by environmental gradients and reflects metabolic constraints or trade-offs that enhance reproductive outputs. While generalizations of life-history relationships across species provide a framework for predicting vulnerability to overexploitation, deciphering patterns of intraspecific variation may also enable recognition of peculiar features of populations that facilitate ecological resilience. This study combines age-based biological data from geographically disparate populations of bluespine unicornfish (Naso unicornis)-the most commercially valuable reef-associated species in the insular Indo-Pacific-to explore the magnitude and drivers of variation in life span and examine the mechanisms enabling peculiar mortality schedules. Longevity and mortality schedules were investigated across eleven locations encompassing a range of latitudes and exploitation levels. The presence of different growth types was examined using back-calculated growth histories from otoliths. Growth-type-dependent mortality (mortality rates associated with particular growth trajectories) was corroborated using population models that incorporated size-dependent competition. We found a threefold geographic variation in life span that was strongly linked to temperature, but not to anthropogenic pressure or ocean productivity. All populations consistently displayed a two-phase mortality schedule, with higher than expected natural mortality rates in earlier stages of post-settlement life. Reconstructed growth histories and population models demonstrated that variable growth types within populations can yield this peculiar biphasic mortality schedule, where fast growers enjoy early reproductive outputs at the expense of greater mortality, and benefits for slow growers derive from extended reproductive outputs over a greater number of annual cycles. This promotes population resilience because individuals can take advantage of cycles of environmental change operating at both short- and long-term scales. Our results highlight a prevailing, fundamental misperception when comparing the life histories of long-lived tropical ectotherms: the seemingly incongruent combination of extended life spans with high mortality rates was enabled by coexistence of variable growth types in a population. Thus, a demographic profile incorporating contrasting growth and mortality strategies obscures the demographic effects of harvest across space or time in N. unicornis and possibly other ectotherms with the combination of longevity and asymptotic growth.

Stable isotope analyses provide the means to examine the trophic role of animals in complex food webs. Here, we used stable isotope analyses to characterize the feeding ecology of reef manta rays (Mobula alfredi) at a remote coral reef in the Western Indian Ocean. Muscle samples ofM. alfrediwere collected from D'Arros Island and St. Joseph Atoll, Republic of Seychelles, in November 2016 and 2017. Prior to analysis, lipid and urea extraction procedures were tested on freeze-dried muscle tissue in order to standardize sample treatment protocols forM. alfredi. The lipid extraction procedure was effective at removing both lipids and urea from samples and should be used in future studies of the trophic ecology of this species. The isotopic signatures of nitrogen (δ15N) and carbon (δ13C) forM. alfredidiffered by year, but did not vary by sex or life stage, suggesting that all individuals occupy the same trophic niche at this coral reef. Furthermore, the isotopic signatures forM. alfredidiffered to those for co-occurring planktivorous fish species also sampled at D'Arros Island and St. Joseph Atoll, suggesting that the ecological niche ofM. alfrediis unique. Pelagic zooplankton were the main contributor (45%) to the diet ofM. alfredi, combined with emergent zooplankton (38%) and mesopelagic prey items (17%). Given the extent of movement that would be required to undertake this foraging strategy, individualM. alfrediare implicated as important vectors of nutrient supply around and to the coral reefs surrounding D'Arros Island and St. Joseph Atoll, particularly where substantial site fidelity is displayed by these large elasmobranchs.

The expanding use of biologging tags in studies of shark movement provides an opportunity to elucidate the context and drivers of fine-scale movement patterns of these predators. In May 2017, we deployed high-resolution biologging tags on four mature female sandbar sharks Carcharhinus plumbeus at Ningaloo Reef for durations ranging between 13 and 25.5 h. Pressure and tri-axial motion sensors within these tags enabled the calculation of dive geometry, swimming kinematics and path tortuosity at fine spatial scales (m-km) and concurrent validation of these behaviors from video recordings. Sandbar sharks oscillated through the water column at shallow dive angles, with gliding behavior observed in the descent phase for all sharks. Continual V-shaped oscillatory movements were occasionally interspersed by U-shaped dives that predominately occurred around dusk. The bottom phase of these U-shaped dives likely occurred on the seabed, with dead-reckoning revealing a highly tortuous, circling track. By combining these fine-scale behavioral observations with existing ecological knowledge of sandbar habitat and diet, we argue that these U-shaped dives are likely to be a strategy for bentho-pelagic foraging. Comparing the diving geometry of sandbar sharks with those of other shark species reveals common patterns in oscillatory swimming. Collectively, the fine-scale movement patterns of sandbar sharks reported here are consistent with results of previous biologging studies that emphasize the role of cost-efficient foraging in sharks.

Waves are thought to provide an important directional cue for hatchlings of marine turtles to navigate through the nearshore zone and to facilitate dispersal to oceanic waters. As the flatback turtle (Natator depressus) is the only species of marine turtle that lacks an oceanic juvenile stage and remains on the continental shelf throughout the entire life cycle, it is possible that hatchlings of this species do not use wave cues for early dispersal. Here, we used a wave flume to examine the response of flatback turtle hatchlings to waves as a cue for nearshore dispersal. We exposed hatchlings to two types of waves (sea and swell waves) differing in height and period commonly experienced at nesting locations and monitored swimming direction (orientation). Hatchlings oriented towards shorter period (3 s) sea waves with both small (6 cm peak to trough) and large (12 cm peak to trough) wave heights. Orientation of hatchlings to longer period (8 s) swell waves only occurred with large (16 cm peak to trough) and not with small (7 cm peak to trough) wave heights. Acceleration generated by waves was the strongest predictor of directional preference in hatchling bearings. There was a positive relationship between maximum acceleration and directional preference, with hatchling bearings more concentrated (r-value 0.98) towards the oncoming wave direction with waves that produced the highest acceleration (sea waves with largest wave heights). These waves were similar to sea waves generated from onshore winds, which was the most common type of wave we measured at a flatback turtle nesting beach. Our study has confirmed that despite lacking an oceanic development stage, flatback hatchlings, like other species of sea turtles, can detect and respond to wave cues, and that the accelerations generated by waves may be a key characteristic of waves that drives orientation.

The ability of predators to switch between hunting and scavenging (facultative scavenging) carries both short-term survival and long-term fitness advantages. However, the mechanistic basis for facultative scavenging remains poorly understood. The co-occurrence of tiger sharks (Galeocerdo cuvier) and green turtles (Chelonia mydas) at Raine Island (Australia), provides an opportunity to examine a top marine predator’s feeding mode in response to seasonal pulses in nesting turtles that offer both hunting and scavenging opportunities. Using satellite telemetry, we evaluated home range overlap between sharks and turtles and quantified their surfacing behavior around Raine Island during the turtle nesting season. We found core home range overlap to be highest during the nesting season. Both sharks and turtles spent significantly more time at the surface in areas of greatest range overlap closest to shore, where turtle density was highest. Both sharks and turtles showed decreased surfacing with increasing distance from Raine Island. Combined with published data on turtle demography at Raine Island, we propose the following: (1) sharks patrol the surface to increase scavenging opportunities on turtle carcasses and intercept weakened individuals after nesting; (2) healthy turtles may not perceive sharks as a major threat and/or other biological factors override anti-predatory responses; and (3) sharks during the nesting season may primarily scavenge on dead turtles individuals rather than actively hunt. Our study results and approach may be applicable to other situations in which direct observations of predator-prey interactions are limited. Every animal encounters dead or dying resources, yet the role of facultative scavenging has been difficult to study, and thus largely overlooked in marine behavioral ecological research. Movement analyses of tiger shark and green turtle movement and surfacing behavior at Raine Island (Australia) suggest that facultative scavenging may be a prevalent, yet underappreciated, feeding strategy in tiger sharks. Our integration of behavioral ecology theory with multi-species electronic tagging provided a valuable approach for investigating predator-prey interactions in situations where direct observations are limited or not possible.

We are grateful to people who contributed to field-work, including Captain Terry Maxwell and his crew on board of 'Osso Blu', as well as all the scientific team from the Australian Institute of Marine Science with special mention to Kim Brooks and the WA Department of Parks and Wildlife. We also thank Peter Mansour at CSIRO for his help with lipid and fatty acid analysis and Ella Clausius for her work in identifying zooplankton samples. Janet A. Ley and 3 anonymous reviewers are thanked for their helpful comments that improved the final manuscript. This research was funded by the Save Our Seas Foundation, Winifred Violet Scott Charitable Trust and Holsworth Wild-life Research Endowment Grants.

Marine protected areas (MPA) are one management tool that can potentially reduce declining shark populations. Protected-area design should be based on detailed movements of target animals; however, such data are lacking for most species. To address this, 25 sharks from three species were tagged with acoustic transmitters and monitored with a network of 103 receivers to determine the use of a protected area at Mangrove Bay, Western Australia. Movements of a subset of 12 individuals ( Carcharhinus melanopterus [ n = 7 ]), C. amblyrhynchos [ n = 2 ], and Negaprion acutidens [ n = 3 ]) were analysed over two years. Residency for all species ranged between 12 and 96%. Carcharhinus amblyrhynchos had C. melanopterus adults that ranged between 0 and 99%. Juvenile sharks had high percentages of position estimates in the MPA (84–99%). Kernel density activity centres for C. melanopterus and C. amblyrhynchos were largely outside the MPA and mean activity space estimates for adults were 12.8 km 2 (±3.12 SE) and 19.6 km 2 (±2.26), respectively. Juveniles had smaller activity spaces: C. melanopterus , 7.2 ±1.33 km 2 ; N. acutidens , 0.6 km 2 (±0.04). Both C. melanopterus and C. amblyrhynchos had peaks in detections during daylight hours (1200 and 0900 h, respectively), whereas N. acutidens had a peak in detections at 0200 h. Long-distance movements were observed for adult C. melanopterus and C. amblyrhynchos , the longest being approximately 275 km. These migrations of C. melanopterus might be related to reproductive behaviours, because they were all observed in adult females during the summer months and provide links between known in-shore aggregation and possible nursery areas. The MPA at Mangrove Bay provided some protection for juvenile and adult reef sharks, although protection is likely greater for juveniles due to their more restricted movements.

The presence of bluestreak cleaner wrasse, Labroides dimidiatus, on coral reefs increases total abundance and biodiversity of reef fishes. The mechanism(s) that cause such shifts in population structure are unclear, but it is possible that young fish preferentially settle into microhabitats where cleaner wrasse are present. As a first step to investigate this possibility, we conducted aquarium experiments to examine whether settlement-stage and young juveniles of ambon damselfish, Pomacentrus amboinensis, selected a microhabitat near a cleaner wrasse (adult or juvenile). Both settlement-stage (0 d post-settlement) and juvenile (~5 weeks post-settlement) fish spent a greater proportion of time in a microhabitat adjacent to L. dimidiatus than in one next to a control fish (a non-cleaner wrasse, Halichoeres melanurus) or one where no fish was present. This suggests that cleaner wrasse may serve as a positive cue during microhabitat selection. We also conducted focal observations of cleaner wrasse and counts of nearby damselfishes (1 m radius) to examine whether newly settled fish obtained direct benefits, in the form of cleaning services, from being near a cleaner wrasse. Although abundant, newly settled recruits (

The coastline of northern Australia may be a refuge for elasmobranchs threatened or extirpated from much of their former ranges across South-East Asia. In this study, we used baited remote underwater video stations to survey the abundance, size and assemblage of elasmobranchs in the Cobourg Marine Park in northern Australia. Two sites were sampled inside the park and one site was sampled outside the park, covering two management zones: open and partially protected. During the austral summer, 85 individuals of 12 species of elasmobranch were observed over 12 days. No significant differences were observed among sites in either size or abundance for common species. Videos were dominated by Carcharhinus melanopterus (relative abundance±s.d., 0.29±0.90h–1), Nebrius ferrugineus (0.03±0.24h–1) and Urogymnus granulatus (0.08±0.28h–1), which comprised >81% of all individuals. Environmental variables had no measurable effect on the abundance of elasmobranchs. The abundance and diversity of elasmobranchs in Cobourg Marine Park is high compared with other similar turbid, inshore areas of northern Australia. The large number of juveniles observed in our surveys also suggests the possibility of a nursery area.

In 2018, the Australian Institute of Marine Science (AIMS) and its partners, conducted an experiment to investigate the effect of exposure to a 3D seismic survey on demersal fishes. The experiment involved the use of a commercial seismic vessel equipped with a 2600 cubic inch air-gun array, sailing a racetrack pattern with eight operational (high exposure zone) and eight inactive (vessel control zone) sail lines, with a 500 m sequential line separation and ≈18 m shot point spacing. The high exposure and vessel control lines were separated by 35 km. Demersal fishes were observed in five sampling surveys over a 6-month period (three surveys before and two after exposure), using acoustic telemetry and stereo baited remote underwater videos systems (BRUVS). The telemetry component included the capture, tagging with acoustic transmitters and release of 387 red emperor (Lutjanus sebae) within two telemetry receiver arrays. These arrays, one in each zone, comprised 37 and 39 acoustic receivers over ≈32 km2, to record movements of tagged fish. The receivers provided near-continuous data on tag locations, and, hence, movement of fish in the area, until removal in December 2018. During each sampling survey, BRUVS were deployed at various distances from the area of the seismic survey. Study results are currently being finalised for presentation.

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches., This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.

The extent of increasing anthropogenic impacts on large marine vertebrates partly depends on the animals’ movement patterns. Effective conservation requires identification of the key drivers of movement including intrinsic properties and extrinsic constraints associated with the dynamic nature of the environments the animals inhabit. However, the relative importance of intrinsic versus extrinsic factors remains elusive. We analyze a global dataset of ∼2.8 million locations from >2,600 tracked individuals across 50 marine vertebrates evolutionarily separated by millions of years and using different locomotion modes (fly, swim, walk/paddle). Strikingly, movement patterns show a remarkable convergence, being strongly conserved across species and independent of body length and mass, despite these traits ranging over 10 orders of magnitude among the species studied. This represents a fundamental difference between marine and terrestrial vertebrates not previously identified, likely linked to the reduced costs of locomotion in water. Movement patterns were primarily explained by the interaction between species-specific traits and the habitat(s) they move through, resulting in complex movement patterns when moving close to coasts compared with more predictable patterns when moving in open oceans. This distinct difference may be associated with greater complexity within coastal microhabitats, highlighting a critical role of preferred habitat in shaping marine vertebrate global movements. Efforts to develop understanding of the characteristics of vertebrate movement should consider the habitat(s) through which they move to identify how movement patterns will alter with forecasted severe ocean changes, such as reduced Arctic sea ice cover, sea level rise, and declining oxygen content., Workshop funding was granted by the University of Western Australia (UWA) Oceans Institute, the Australian Institute of Marine Science (AIMS), and King Abdullah University of Science and Technology (KAUST). A.M.M.S. was supported by Australian Research Council Grant DE170100841 and an Indian Ocean Ocean Marine Research Centre (UWA, AIMS, Commonwealth of Scientific and Industrial Research Organisation) fellowship. J.P.R., V.M.E., and J.F.G. were supported by Agencia Estatal de Investigación (AEI, Spain) and Fondo Europeo de Desarrollo Regional (FEDER) through project Spatiotemporality in Sociobological Interactions, Models and Methods (SPASIMM) (FIS2016-80067-P AEI/FEDER, European Union), and by research funding from KAUST. J.P.R. was supported by Ministerio de Educación, Cultura y Deporte (Formación de Profesorado Universitario Grant, Spain). D.W.S. was supported by the UK Natural Environment Research Council and Save Our Seas Foundation. N.Q. was supported by Fundação para a Ciência e Tecnologia (Portugal). M.M.C.M. was supported by a Coordenação de Aperfeiçoamento de pessoal de Nível Superior fellowship (Ministry of Education).

In recent decades, biologists have sought to tag animals with various sensors to study aspects of their behavior otherwise inaccessible from controlled laboratory experiments. Despite this, chemical information, both environmental and physiological, remains challenging to collect despite its tremendous potential to elucidate a wide range of animal behaviors. In this work, we explore the design, feasibility, and data collection constraints of implantable, near-infrared fluorescent nanosensors based on DNA-wrapped single-wall carbon nanotubes (SWNT) embedded within a biocompatible poly(ethylene glycol) diacrylate (PEGDA) hydrogel. These sensors are enabled by Corona Phase Molecular Recognition (CoPhMoRe) to provide selective chemical detection for marine organism biologging. Riboflavin, a key nutrient in oxidative phosphorylation, is utilized as a model analyte in in vitro and ex vivo tissue measurements. Nine species of bony fish, sharks, eels, and turtles were utilized on site at Oceanogràfic in Valencia, Spain to investigate sensor design parameters, including implantation depth, sensor imaging and detection limits, fluence, and stability, as well as acute and long-term biocompatibility. Hydrogels were implanted subcutaneously and imaged using a customized, field-portable Raspberry Pi camera system. Hydrogels could be detected up to depths of 7 mm in the skin and muscle tissue of deceased teleost fish ( Sparus aurata and Stenotomus chrysops) and a deceased catshark ( Galeus melastomus). The effects of tissue heterogeneity on hydrogel delivery and fluorescence visibility were explored, with darker tissues masking hydrogel fluorescence. Hydrogels were implanted into a living eastern river cooter ( Pseudemys concinna), a European eel ( Anguilla anguilla), and a second species of catshark ( Scyliorhinus stellaris). The animals displayed no observable changes in movement and feeding patterns. Imaging by high-resolution ultrasound indicated no changes in tissue structure in the eel and catshark. In the turtle, some tissue reaction was detected upon dissection and histopathology. Analysis of movement patterns in sarasa comet goldfish ( Carassius auratus) indicated that the hydrogel implants did not affect swimming patterns. Taken together, these results indicate that this implantable form factor is a promising technique for biologging using aquatic vertebrates with further development. Future work will tune the sensor detection range to the physiological range of riboflavin, develop strategies to normalize sensor signal to account for the optical heterogeneity of animal tissues, and design a flexible, wearable device incorporating optoelectronic components that will enable sensor measurements in moving animals. This work advances the application of nanosensors to organisms beyond the commonly used rodent and zebrafish models and is an important step toward the physiological biologging of aquatic organisms.

Large-bodied pelagic ectotherms such as sharks need to maintain internal temperatures within a favourable range in order to maximise performance and be cost-efficient foragers. This implies that behavioural thermoregulation should be a key feature of the movements of these animals, although field evidence is limited. We used depth and temperature archives from pop-up satellite tags to investigate the role of temperature in driving vertical movements of 16 oceanic whitetip sharks, Carcharhinus longimanus, (OWTs). Spectral analysis, linear mixed modelling, segmented regression and multivariate techniques were used to examine the effect of mean sea surface temperature (SST) and mixed layer depth on vertical movements. OWTs continually oscillated throughout the upper 200 m of the water column. In summer when the water column was stratified with high SSTs, oscillations increased in amplitude and cycle length and sharks reduced the time spent in the upper 50 m. In winter when the water column was cooler and well-mixed, oscillations decreased in amplitude and cycle length and sharks frequently occupied the upper 50 m. SSTs of 28 oC marked a distinct change in vertical movements and the onset of thermoregulation strategies. Our results have implications for the ecology of these animals in a warming ocean.