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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.

Individual growth rate is one of the key traits that determine the productivity of populations. Chronological approaches that relate time series of growth and climate information present the opportunity to identify important climatic drivers of demography and thereby understand the likely impact of climate change. We constructed otolith chronologies (a proxy for somatic growth) to examine synchrony of growth patterns within and between two mesopredatory fishes (Lutjanus bohar and L. gibbus) in the remote Chagos Archipelago, Indian Ocean. We then used mixed-model and pathway analysis to relate growth responses to a suite of climatic and environmental factors to determine the extent to which variation in inter-annual growth could be predicted at individual and population levels. Our models explained up to half the variance associated with annual growth at the level of populations. Significant environmental drivers of growth differed between species, as did the spatial scale of these drivers: L. gibbus exhibited a strong relationship with regional ocean temperature, whereas growth of L. bohar was correlated with the Pacific Decadal Oscillation, suggesting influential teleconnections between ocean basins as an underlying predictor of productivity of fish populations. Our results demonstrate that (1) synchronous growth stemming from relationships with climate factors may be suppressed at very low latitudes; (2) closely related species may respond to very different environmental stimuli; and (3) within the same environment, the scale of influential drivers may be local in nature or reflect oceanographic processes stretching across entire ocean basins. We demonstrate that biochronological approaches are effective tools for reconstructing relationships between climate variability and fish growth even in tropical regions where seasonality is low, and these methods can be valuable for forecasting population-level responses to projected climate change.

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.

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.

The recovery of communities of predatory fishes within a no‐take marine reserve after the eradication of illegal fishing provides an opportunity to examine the role of sharks and other large‐bodied mesopredatory fishes in structuring reef fish communities. We used baited remote underwater video stations to investigate whether an increase in sharks was associated with a change in structure of the mesopredatory fish community at Ashmore Reef, Western Australia. We found an almost fourfold increase in shark abundance in reef habitat from 0.64 hr−1 ± 0.15 SE in 2004, when Ashmore Reef was being fished illegally, to 2.45 hr−1 ± 0.37 in 2016, after eight years of full‐time enforcement of the reserve. Shark recovery in reef habitat was accompanied by a two and a half‐fold decline in the abundance of small mesopredatory fishes (≤50 cm TL) (14.00 hr−1 ± 3.79 to 5.6 hr−1 ± 1.20) and a concomitant increase in large mesopredatory fishes (≥100 cm TL) from 1.82 hr−1 ± 0.48 to 4.27 hr−1 ± 0.93. In contrast, near‐reef habitats showed an increase in abundance of large mesopredatory fishes between years (2.00 hr−1 ± 0.65 to 4.56 hr−1 ± 1.11), although only smaller increases in sharks (0.67 hr−1 ± 0.25 to 1.22 hr−1 ± 0.34) and smaller mesopredatory fishes. Although the abundance of most mesopredatory groups increased with recovery from fishing, we suggest that the large decline of small mesopredatory fish in reef habitat was mostly due to higher predation pressure following the increase in sharks and large mesopredatory fishes. At the regional scale, the structure of fished communities at Ashmore Reef in 2004 resembled those of present day Scott Reefs, where fishing still continues today. In 2016, Ashmore fish communities resembled those of the Rowley Shoals, which have been protected from fishing for decades., We observed abundance and community composition of shark and mesopredatory reef fish at Ashmore Reef in Western Australia, before and after recovery from illegal fishing pressure. After eight years of recovery, there was a large decrease in small (≤50 cm TL) mesopredatory reef fish abundance and a concomitant increase in shark and large (>100 cm TL) mesopredatory fish abundance in reef habitat. Our findings provide support for fish community restructuring with reef shark recovery, which has implications for management time frames of marine protected areas.

Growing human populations are driving the development of coastal infrastructure such as port facilities. Here, we used passive acoustic telemetry to examine the effects of a jetty and artificial light on the rates of predation of flatback turtle (Natator depressus) hatchlings as they disperse through nearshore waters. When released near a jetty, around 70% of the tagged hatchlings were predated before they could transit the nearshore, irrespective of the presence or absence of artificial light. Only 3 to 23% of hatchlings encountered predators at a second study site nearby where there was no jetty and a similar amount of nesting activity. Evidence for predation was provided by rapid tag detachment due to prey handling by a predator or the extensive movement of the tags within the receiver array suggesting that the tag (and hatchling) was inside the stomach of a predator. We found that 70% of the fish predators that consumed tags used the jetty as a refuge during the day and expanded their range along nearshore waters at night, predating on hatchlings in areas adjacent to the jetty with the highest nesting density. Sampling of potential predators including lutjanid reef fishes under the jetty revealed the presence of turtle hatchlings in their gut contents. By providing daytime refuges for predators, nearshore structures such as jetties have the potential to concentrate predators and they may pose a significant threat to populations of vulnerable species. Such effects must be taken into consideration when assessing the environmental impacts associated with these structures.

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.

Summary Proximity and size of the nearest market (‘market gravity’) have been shown to have strong negative effects on coral reef fish communities that can be mitigated by the establishment of closed areas. However, moray eels are functionally unique predators that are generally not subject to targeted fishing and should therefore not directly be affected by these factors. We used baited remote underwater video systems to investigate associations between morays and anthropogenic, habitat, and ecological factors in the Caribbean region. Market gravity had a positive effect on morays, while the opposite pattern was observed in a predator group subject to exploitation (sharks). Environmental DNA analyses corroborated the positive effect of market gravity on morays. We hypothesize that the observed pattern could be the indirect result of the depletion of moray competitors and predators near humans., Graphical Abstract, Highlights • Baited remote underwater videos and environmental DNA were used to assess morays • Market gravity had a strong positive effect on moray abundance • Morays and sharks were negatively associated • Lack of competitors and predators may explain increased morays on reefs near humans, Environmental science; ecology; biological sciences; zoology; animals; ethology

[Abstract] Oceans have become substantially noisier since the Industrial Revolution. Shipping, resource exploration, and infrastructure development have increased the anthrophony (sounds generated by human activities), whereas the biophony (sounds of biological origin) has been reduced by hunting, fishing, and habitat degradation. Climate change is affecting geophony (abiotic, natural sounds). Existing evidence shows that anthrophony affects marine animals at multiple levels, including their behavior, physiology, and, in extreme cases, survival. This should prompt management actions to deploy existing solutions to reduce noise levels in the ocean, thereby allowing marine animals to reestablish their use of ocean sound as a central ecological trait in a healthy ocean., [Background] Sound is the sensory cue that travels farthest through the ocean and is used by marine animals, ranging from invertebrates to great whales, to interpret and explore the marine environment and to interact within and among species. Ocean soundscapes are rapidly changing because of massive declines in the abundance of sound-producing animals, increases in anthropogenic noise, and altered contributions of geophysical sources, such as sea ice and storms, owing to climate change. As a result, the soundscape of the Anthropocene ocean is fundamentally different from that of preindustrial times, with anthropogenic noise negatively impacting marine life., [Advances] We find evidence that anthropogenic noise negatively affects marine animals. Strong evidence for such impacts is available for marine mammals, and some studies also find impacts for fishes and invertebrates, marine birds, and reptiles. Noise from vessels, active sonar, synthetic sounds (artificial tones and white noise), and acoustic deterrent devices are all found to affect marine animals, as are noise from energy and construction infrastructure and seismic surveys. Although there is clear evidence that noise compromises hearing ability and induces physiological and behavioral changes in marine animals, there is lower confidence that anthropogenic noise increases the mortality of marine animals and the settlement of their larvae., [Outlook] Anthropogenic noise is a stressor for marine animals. Thus, we call for it to be included in assessments of cumulative pressures on marine ecosystems. Compared with other stressors that are persistent in the environment, such as carbon dioxide emitted to the atmosphere or persistent organic pollutants delivered to marine ecosystems, anthropogenic noise is typically a point-source pollutant, the effects of which decline swiftly once sources are removed. The evidence summarized here encourages national and international policies to become more ambitious in regulating and deploying existing technological solutions to mitigate marine noise and improve the human stewardship of ocean soundscapes to maintain a healthy ocean. We provide a range of solutions that may help, supported by appropriate managerial and policy frameworks that may help to mitigate impacts on marine animals derived from anthropogenic noise and perturbations of soundscapes., This research was funded by KAUST through the Tarek Ahmed Juffali Research Chair in Red Sea Ecology and baseline funding to C.M.D.

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.

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.

International audience; Coastal populations of maritime countries in eastern Africa rely on fish as a primary source of protein, but baseline information on the abundance of fish communities on these coastlines is often lacking. We used baited remote underwater video stations to compare the abundance and diversity of reef fishes targeted by fishing at two sites in southern Mozambique, one at Lighthouse Reef within the Bazaruto Archipelago National Park and the other to the south at San Sebastian Reef on the San Sebastian Peninsula. Fish that are known targets of fisheries (mostly small-scale and artisanal) had an abundance that was almost three-times greater at San Sebastian Reef (80.22 ind. h–1 [SE 18.00]) than at Lighthouse Reef (29.70 ind. h–1 [SE 8.91]). Similarly, there was greater mean species richness at San Sebastian Reef (38.74 species h–1 [SE 2.79]) than at Lighthouse Reef (25.37 species h–1 [SE 3.66]). The main drivers of targeted fish abundance were habitat and depth, with shallow (

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Fishing has had a profound impact on global reef shark populations, and the absence or presence of sharks is strongly correlated with national socio-economic conditions and reef governance. Decades of overexploitation have devastated shark populations, leaving considerable doubt as to their ecological status(1,2). Yet much of what is known about sharks has been inferred from catch records in industrial fisheries, whereas far less information is available about sharks that live in coastal habitats(3). Here we address this knowledge gap using data from more than 15,000 standardized baited remote underwater video stations that were deployed on 371 reefs in 58 nations to estimate the conservation status of reef sharks globally. Our results reveal the profound impact that fishing has had on reef shark populations: we observed no sharks on almost 20% of the surveyed reefs. Reef sharks were almost completely absent from reefs in several nations, and shark depletion was strongly related to socio-economic conditions such as the size and proximity of the nearest market, poor governance and the density of the human population. However, opportunities for the conservation of reef sharks remain: shark sanctuaries, closed areas, catch limits and an absence of gillnets and longlines were associated with a substantially higher relative abundance of reef sharks. These results reveal several policy pathways for the restoration and management of reef shark populations, from direct top-down management of fishing to indirect improvement of governance conditions. Reef shark populations will only have a high chance of recovery by engaging key socio-economic aspects of tropical fisheries.

Coral reefs worldwide are increasingly damaged by anthropogenic stressors, necessitating novel approaches for their management. Maintaining healthy fish communities counteracts reef degradation, but degraded reefs smell and sound less attractive to settlement-stage fishes than their healthy states. Here, using a six-week field experiment, we demonstrate that playback of healthy reef sound can increase fish settlement and retention to degraded habitat. We compare fish community development on acoustically enriched coral-rubble patch reefs with acoustically unmanipulated controls. Acoustic enrichment enhances fish community development across all major trophic guilds, with a doubling in overall abundance and 50% greater species richness. If combined with active habitat restoration and effective conservation measures, rebuilding fish communities in this manner might accelerate ecosystem recovery at multiple spatial and temporal scales. Acoustic enrichment shows promise as a novel tool for the active management of degraded coral reefs., Healthy coral reefs have an acoustic signature known to be attractive to coral and fish larvae during settlement. Here the authors use playback experiments in the field to show that healthy reef sounds can increase recruitment of juvenile fishes to degraded coral reef habitat, suggesting that acoustic playback could be used as a reef management strategy.

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.

We thank the Western Australian Departments of Fisheries, Parks and Wildlife (DPaW), the Commonwealth Department of Sustainability, Environment, Water, Population and Communities for arranging permits to conduct research at the Scott Reefs and the Rowley Shoals. We acknowledge the crew on board the RV 'Solander,' Kim Brooks, Paul Tinkler and numerous volunteers for aid in the field. Thanks also to Paddy Ryan who provided images for the figures. Special thanks to Sarah Hirth, Gammon Koval, Rachel Skubel and Marcelo Costa Lopez for help with some figures. This research was funded in part by the Australian Institute of Marine Science, an International Postgraduate Research Scholarship to S.C.B., the Save our Seas Foundation and the University of Western Australia, Perth, under UWA Ethics Approvals: RA3/100/1279, RA3/100/1172. We thank Ashley Frisch and several reviewers who provided valuable comments that improved our manuscript.

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.

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.

Biochronologies provide important insights into the growth responses of fishes to past variability in physical and biological environments and, in so doing, allow modelling of likely responses to climate change in the future. We examined spatial variability in the key drivers of inter-annual growth patterns of a widespread, tropical snapper, Lutjanus bohar, at similar tropical latitudes on the north-western and north-eastern coasts of the continent of Australia. For this study, we developed biochronologies from otoliths that provided proxies of somatic growth and these were analysed using mixed-effects models to examine the historical drivers of growth. Our analyses demonstrated that growth patterns of fish were driven by different climatic and biological factors in each region, including Pacific Ocean climate indices, regional sea level and the size structure of the fish community. Our results showed that the local oceanographic and biological context of reef systems strongly influenced the growth of L. bohar and that a single age-related growth trend cannot be assumed for separate populations of this species that are likely to experience different environmental conditions. Generalised predictions about the growth response of fishes to climate change will thus require adequate characterisation of the spatial variability in growth determinants likely to be found throughout the range of species that have cosmopolitan distributions.

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.

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.

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 (

Funding was provided from the Paul G. Allen Foundation through the Global FinPrint Project.

To demonstrate conservation effects resulting from marine protected areas, many studies rely on spatial comparisons between areas afforded different levels of protection. These spatial comparisons can be confounded if the habitat and reef size are dissimilar and not accounted for in the statistical analysis. Taking into account reef size (obtained from multibeam sonar data) and benthic habitat structure, this research tested the effect of management zonation (No-take Sanctuary Zone = NTSZ; Controlled Pelagic Zone = CPZ) on the population structure (relative abundance and average biomass) of six fish species in the iSimangaliso Wetland Park, South Africa. Furthermore, this study tested the effect of ignoring reef size in spatial comparisons. Our results showed that reef size had a significant positive effect on the relative abundance and average biomass of most, but not all species. When reef size was included in the models, the results showed that two of the six species presented no effect of management zone; two appeared to be directly affected by the permitted (past and present) fishing activity in the CPZ; and the last two species appeared to be affected by the disturbance caused by the diving and/or boating activity in the CPZ. Excluding reef size from the analysis consistently resulted in the predicted relative abundance and average biomass decreasing in the CPZ and increasing in the NTSZ. This effect was most marked in the average biomass data, as the management zone effect changed from negligible to significant for five of the six species. Our results highlight the importance of accounting for the reef size, or area of suitable habitat, when conducting spatial comparisons among species and illustrate the potential impact of the trade-off required to accommodate human needs within protected spaces.

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.

Noise produced by anthropogenic activities is increasing in many marine ecosystems. We investigated the effect of playback of boat noise on fish cognition. We focused on noise from small motorboats, since its occurrence can dominate soundscapes in coastal communities, the number of noise-producing vessels is increasing rapidly and their proximity to marine life has the potential to cause deleterious effects. Cognition—or the ability of individuals to learn and remember information—is crucial, given that most species rely on learning to achieve fitness-promoting tasks, such as finding food, choosing mates and recognizing predators. The caveat with cognition is its latent effect: the individual that fails to learn an important piece of information will live normally until the moment where it needs the information to make a fitness-related decision. Such latent effects can easily be overlooked by traditional risk assessment methods. Here, we conducted three experiments to assess the effect of boat noise playbacks on the ability of fish to learn to recognize predation threats, using a common, conserved learning paradigm. We found that fish that were trained to recognize a novel predator while being exposed to ‘reef + boat noise’ playbacks failed to subsequently respond to the predator, while their ‘reef noise’ counterparts responded appropriately. We repeated the training, giving the fish three opportunities to learn three common reef predators, and released the fish in the wild. Those trained in the presence of ‘reef + boat noise’ playbacks survived 40% less than the ‘reef noise’ controls over our 72 h monitoring period, a performance equal to that of predator-naive fish. Our last experiment indicated that these results were likely due to failed learning, as opposed to stress effects from the sound exposure. Neither playbacks nor real boat noise affected survival in the absence of predator training. Our results indicate that boat noise has the potential to cause latent effects on learning long after the stressor has gone.

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).

Reef sharks may influence the foraging behaviour of mesopredatory teleosts on coral reefs via both risk effects and competitive exclusion. We used a "natural experiment" to test the hypothesis that the loss of sharks on coral reefs can influence the diet and body condition of mesopredatory fishes by comparing two remote, atoll-like reef systems, the Rowley Shoals and the Scott Reefs, in northwestern Australia. The Rowley Shoals are a marine reserve where sharks are abundant, whereas at the Scott Reefs numbers of sharks have been reduced by centuries of targeted fishing. On reefs where sharks were rare, the gut contents of five species of mesopredatory teleosts largely contained fish while on reefs with abundant sharks, the same mesopredatory species consumed a larger proportion of benthic invertebrates. These measures of diet were correlated with changes in body condition, such that the condition of mesopredatory teleosts was significantly poorer on reefs with higher shark abundance. Condition was defined as body weight, height and width for a given length and also estimated via several indices of condition. Due to the nature of natural experiments, alternative explanations cannot be discounted. However, the results were consistent with the hypothesis that loss of sharks may influence the diet and condition of mesopredators and by association, their fecundity and trophic role. Regardless of the mechanism (risk effects, competitive release, or other), our findings suggest that overfishing of sharks has the potential to trigger trophic cascades on coral reefs and that further declines in shark populations globally should be prevented to protect ecosystem health.

Alternative livelihood projects are criticised as having minimal effect on biodiversity conservation. Studies are rare and where success is claimed, outcomes and reasons why projects work, have not been documented. Livelihoods are an essential element of sustainable integrated coastal management, an accepted framework for conserving coral reefs and marine resources in the tropics. It is not known whether alternative livelihood projects contribute to the goal of improving biodiversity conservation through sustainable integrated coastal management. Here, we examine Oslob Whale Sharks, an alternate livelihoods project in the Philippines built on provisioning whale sharks for community based dive tourism. We investigate how Oslob Whale Sharks contributes to sustainable integrated coastal management and whether it has any effect on biodiversity conservation. Using key stakeholder interviews with artisanal fishers, their community, local politicians and government, we found that Oslob Whale Sharks contributes to all nine factors required for sustainable integrated coastal management. Fishers and local authorities report their perception that whale sharks are protected from poaching and finning and destructive fishing has decreased, while fish abundance, pelagic fish species and catch have increased. Our findings further suggest that as there is little evidence that this type of tourism has any negative impacts on the biology or behaviour of whale sharks, Oslob Whale Sharks provides sustainable livelihoods and a delivery mechanism for sustainable integrated coastal management.

We report observations of a novel feeding behaviour in the moray eel Gymnothorax favagineus (Bloch & Schneider, 1801) and a previously undocumented application of “knotting” behaviour in G. fimbriatus (Bennett, 1832). Moray eels were filmed by baited remote underwater video systems (BRUVS) at the Scott Reefs, a remote group of atoll-like reefs on the edge of the continental shelf in tropical, northwestern Australia. Two behaviours were observed as the moray eels tried to dislodge food from a bait bag: (1) G. favagineus used its tail as a “paddle” to gain leverage on the bag, and (2) G. fimbriatus tied a knot in its tail in order to extract food from the bag. Our observations suggest that morays have an extensive behavioural repertoire for manipulating and extracting large prey items from the interstices of the reefs where they typically hunt.

Little information is available on the movements and behaviour of tropical rays despite their potential ecological roles and economic value as a fishery and a tourism resource. A description of the movement patterns and site fidelity of juvenile rays within a coral reef environment is provided in this study. Acoustic telemetry was used to focus on the use of potential nursery areas and describe movement patterns of 16 individuals of four species monitored for 1–21 months within an array of 51 listening stations deployed across a lagoon, reef crest, and reef slope at Mangrove Bay, Ningaloo Reef, Western Australia. Juveniles used a small (< 1 km2), shallow (1–2 m depth) embayment where three receivers recorded 60–80 % of total detections of tagged animals, although individuals of all species moved throughout the array and beyond the lagoon to the open reef slope. Detections at these primary sites were more frequent during winter and when water temperatures were highest during the day. Long-term use of coastal lagoons by juvenile rays suggests that they provide an important habitat for this life stage. Current marine park zoning appears to provide an effective protection for juveniles within this area.

Dietary characteristics and the degree of dietary partitioning by five species of sympatric stingray were assessed using stomach content and sediment analyses within a coral reef lagoon at Ningaloo Reef, Western Australia (the cowtail Pastinachus atrus, blue-spotted fantail Taeniura lymma, blue-spotted mask Neotrygon kuhlii, porcupine Urogymnus asperrimus rays and the reticulate whipray Himantura uarnak). A total of 2804 items were recovered from the stomachs of 170 rays and 3215 individual taxa from the environment, which were used in selectivity analyses. Twenty-four prey taxa were identified from stomach contents and pooled into 10 taxonomic categories for analysis, of which annelids, prawns, brachyurans and bivalves were the most abundant, together accounting for 96% of the diet. Himantura uarnak had the greatest interspecific dissimilarity in diet, consuming a larger proportion of crustaceans, notably penaeids (41% of total diet) than the other four species of rays, all of which had diets dominated by annelids (71-82% of total diet). Crustacean specialization by H. uarnak may exist to maximize resources and reduce competition among sympatric species. The remaining species may partition resources on the basis of space, rather than diet.

Understanding the movements of turtle hatchings is essential for improved understanding of dispersal behaviour and ultimately survivorship, life history strategies and population connectivity. Yet investigation of in-water movement has been hampered by the small size of hatchlings relative to the size of available tracking technologies. This has resulted in the use of labour intensive visual tracking methods, or active tracking methods with high transmitter to body weight ratios. These methods are confounded by the presence of the observer, the size of the tag, usual small treatment sample sizes and studies that are constrained to daylight hours when turtles hatch predominantly at night. Passive acoustic monitoring using new miniature tags can overcome these limitations. We tested the effectiveness of active and passive acoustic tracking in monitoring turtle hatchling movement in order to measure the influence of artificial light on newly hatched turtles once they enter the water. A Vemco VR2W Positioning System (VPS) comprising an array of 18 VR2W receivers was deployed in the surf zone to detect signals from acoustic-coded transmitters (1.14 ± 0.06% of body mass) attached to 26 flatback turtle hatchlings released into the array. A total of 1328 detections were recorded for 22 hatchlings with turtles spending a mean of 16.63 ± 5.89 min in the array. The test detection range for this technology in the surf-zone was 50–100 m and was influenced by wave noise and shallow deployment. Cyclonic conditions hampered the experiment and resulted in an inconclusive test of light effects. Three additional instrumented flatback hatchlings were followed in a small boat using a mobile acoustic receiver and directional hydrophone up to 2 km from shore. Passive acoustic monitoring is a viable technology for tracking small marine animals and removes many of the confounding effects of other telemetry methods. It has great potential to examine natural and anthropogenic factors influencing orientation and behaviour during a crucial stage in turtle life history — their initial movement from the beach through predator-rich, near shore waters. While the data obtained by passive acoustic monitoring is limited in its spatio-temporal coverage, being constrained by the size of the array, active acoustic tracking can be applied over larger scales. Such studies will be particularly important for assessing the impacts of anthropogenic pressures that have changed the natural light, noise or wave environments and for providing behavioural data to improve and validate bio-physical models of the migration and dispersal of young turtles.

Ten years have passed since the last synopsis of whale shark Rhincodon typus biogeography. While a recent review of the species' biology and ecology summarized the vast data collected since then, it is clear that information on population geographic connectivity, migration and demography of R. typus is still limited and scattered. Understanding R. typus migratory behaviour is central to its conservation management considering the genetic evidence suggesting local aggregations are connected at the generational scale over entire ocean basins. By collating available data on sightings, tracked movements and distribution information, this review provides evidence for the hypothesis of broad-scale connectivity among populations, and generates a model describing how the world's R. typus are part of a single, global meta-population. Rhincodon typus occurrence timings and distribution patterns make possible a connection between several aggregation sites in the Indian Ocean. The present conceptual model and validating data lend support to the hypothesis that R. typus are able to move among the three largest ocean basins with a minimum total travelling time of around 2-4 years. The model provides a worldwide perspective of possible R. typus migration routes, and suggests a modified focus for additional research to test its predictions. The framework can be used to trim the hypotheses for R. typus movements and aggregation timings, thereby isolating possible mating and breeding areas that are currently unknown. This will assist endeavours to predict the longer-term response of the species to ocean warming and changing patterns of human-induced mortality.

This study details a simple and cost-effective means of attaching acoustic transmitters to coral reef sharks and stingrays, which potentially allows for retrieval and reuse on completion of tracks. Between 2008 and 2011, galvanised timed releases were trialled in both static field tests and on blacktip reef sharks Carcharhinus melanopterus, cowtail Pastinachus atrus, and porcupine Urogymnus asperrimus rays in Coral Bay (−23°08′41″, 113°45′53″), Western Australia. The timed releases remained attached to animals for the duration required for tracking and in four out of five deployments transmitters were recovered after release from the animals. The use of modified Rototags for sharks and stainless steel darts for stingrays allowed rapid and effective attachment to animals, with limited impact on their welfare in the short term. External attachment for short-term tracking of coral reef-associated elasmobranchs should be considered as a complementary option to internal placement of transmitters in animals either by surgery or by ingestion.

Body size and age at maturity are indicative of the vulnerability of a species to extinction. However, they are both difficult to estimate for large animals that cannot be restrained for measurement. For very large species such as whale sharks, body size is commonly estimated visually, potentially resulting in the addition of errors and bias. Here, we investigate the errors and bias associated with total lengths of whale sharks estimated visually by comparing them with measurements collected using a stereo-video camera system at Ningaloo Reef, Western Australia. Using linear mixed-effects models, we found that visual lengths were biased towards underestimation with increasing size of the shark. When using the stereo-video camera, the number of larger individuals that were possibly mature (or close to maturity) that were detected increased by approximately 10%. Mean lengths calculated by each method were, however, comparable (5.002 ± 1.194 and 6.128 ± 1.609 m, s.d.), confirming that the population at Ningaloo is mostly composed of immature sharks based on published lengths at maturity. We then collated data sets of total lengths sampled from aggregations of whale sharks worldwide between 1995 and 2013. Except for locations in the East Pacific where large females have been reported, these aggregations also largely consisted of juveniles (mean lengths less than 7 m). Sightings of the largest individuals were limited and occurred mostly prior to 2006. This result highlights the urgent need to locate and quantify the numbers of mature male and female whale sharks in order to ascertain the conservation status and ensure persistence of the species.

After a pelagic larval phase, settlement-stage coral reef fish must locate a suitable reef habitat for juvenile life. Reef noise, produced by resident fish and invertebrates, provides an important cue for orientation and habitat selection during this process, which must often occur in environments impacted by anthropogenic noise. We adapted an established field-based protocol to test whether recorded boat noise influenced the settlement behavior of reef fish. Fewer fish settled to patch reefs broadcasting boat + reef noise compared with reef noise alone. This study suggests that boat noise, now a common feature of many reefs, can compromise critical settlement behavior of reef fishes.

We examined the effect of artificial light on the near shore trajectories of turtle hatchlings dispersing from natal beaches. Green turtle (Chelonia mydas) hatchlings were tagged with miniature acoustic transmitters and their movements tracked within an underwater array of 36 acoustic receivers placed in the near shore zone. A total of 40 hatchlings were tracked, 20 of which were subjected to artificial light during their transit of the array. At the same time, we measured current speed and direction, which were highly variable within and between experimental nights and treatments. Artificial lighting affected hatchling behaviour, with 88% of individual trajectories oriented towards the light and spending, on average, 23% more time in the 2.25 ha tracking array (19.5 ± 5 min) than under ambient light conditions (15.8 ± 5 min). Current speed had little to no effect on the bearing (angular direction) of the hatchling tracks when artificial light was present, but under ambient conditions it influenced the bearing of the tracks when current direction was offshore and above speeds of approximately 32.5 cm s−1. This is the first experimental evidence that wild turtle hatchlings are attracted to artificial light after entering the ocean, a behaviour that is likely to subject them to greater risk of predation. The experimental protocol described in this study can be used to assess the effect of anthropogenic (light pollution, noise, etc.) and natural (wave action, current, wind, moonlight) influences on the in-water movements of sea turtle hatchlings during the early phase of dispersal.

Background The seasonal aggregations of whale sharks that occur at coastal sites throughout the tropics are the focus of growing ecotourism industries. Genetic and modelling studies suggest that these aggregations may be linked by migration, although the temporal and spatial scales at which this occurs is unknown. Here, we utilized a continuously expanding photoidentification database collected by citizen scientists and researchers to assess connectivity and residency patterns of five whale shark aggregation sites across the entire Indian Ocean at timescales of up to a decade. We also investigated the effectiveness of such an approach in detecting different levels of migration given the population size at each aggregation site. Approach We used the semi-automated program I3S (Individual Interactive Identification System) to compare 6,519 photographs of the unique natural marking patterns of individual whale sharks collected from aggregations at Mozambique, the Seychelles, the Maldives, Christmas Island (Australia) and Ningaloo Reef (Australia). We searched the database for matches between aggregations (migration) and matches between years within aggregations (residency). A Monte Carlo simulation approach utilizing population sizes of aggregations reported by previous studies was used to examine the sample sizes that would be required to reliably detect varying levels of migration rates among four of these aggregations. Results We found no evidence of connectivity of whale shark aggregations at ocean-basin scales within the time frame of the study, and evidence for only limited connectivity at regional (100s–1000s km) scales. A male whale shark sampled in January 2010 at Mozambique was resighted eight months later in the Seychelles and was the only one of 1,724 individuals to be photographed at more than one site. On average, 35% of individuals were re-sighted at the same site in more than one year. The Monte Carlo simulation study showed that the power of this photo-identification approach was strongly dependent on both the number of individuals identified in aggregations each year and the size of resident populations. The simulation also indicated that there was a higher chance of detecting migrants (if they were present) in aggregations at Ningaloo Reef and the Maldives than the Seychelles and Mozambique given the current numbers of individuals identified each year. Conclusions The weight of evidence from both our photo-identification study and previous tagging studies suggests regional or small-scale movements (10–100s km) may be more common in whale sharks than movement at ocean-basin scales. We recommend that the management of whale sharks in the Indian Ocean occur at regional scales, and photo-identification databases are expanded to include additional sampling sites within each region.

Genetic and modelling studies suggest that seasonal aggregations of whale sharks ( Rhincodon typus ) at coastal sites in the tropics may be linked by migration. Here, we used photo-identification (photo-ID) data collected by both citizen scientists and researchers to assess the connectedness of five whale shark aggregation sites across the entire Indian Ocean at timescales of up to a decade. We used the semi-automated program I 3 S (Individual Interactive Identification System) to compare photographs of the unique natural marking patterns of individual whale sharks collected from aggregations at Mozambique, the Seychelles, the Maldives, Christmas Island (Australia) and Ningaloo Reef (Australia). From a total of 6519 photos, we found no evidence of connectivity of whale shark aggregations at ocean-basin scales within the time frame of the study and evidence for only limited connectivity at regional (hundreds to thousands of kilometres) scales. A male whale shark photographed in January 2010 at Mozambique was resighted eight months later in the Seychelles and was the only one of 1724 individuals in the database to be photographed at more than one site. On average, 35% of individuals were resighted at the same site in more than one year. A Monte Carlo simulation study showed that the power of this photo-ID approach to document patterns of emigration and immigration was strongly dependent on both the number of individuals identified in aggregations and the size of resident populations.

1. With the global increase in CO2 emissions, there is a pressing need for studies aimed at understanding the effects of ocean acidification on marine ecosystems. Several studies have reported that exposure to CO2 impairs chemosensory responses of juvenile coral reef fishes to predators. Moreover, one recent study pointed to impaired responses of reef fish to auditory cues that indicate risky locations. These studies suggest that altered behaviour following exposure to elevated CO2 is caused by a systemic effect at the neural level. 2. The goal of our experiment was to test whether juvenile damselfish Pomacentrus amboinensis exposed to different levels of CO2 would respond differently to a potential threat, the sight of a large novel coral reef fish, a spiny chromis, Acanthochromis polyancanthus, placed in a watertight bag. 3. Juvenile damselfish exposed to 440 (current day control), 550 or 700 μatm CO2 did not differ in their response to the chromis. However, fish exposed to 850 μatm showed reduced antipredator responses; they failed to show the same reduction in foraging, activity and area use in response to the chromis. Moreover, they moved closer to the chromis and lacked any bobbing behaviour typically displayed by juvenile damselfishes in threatening situations. 4. Our results are the first to suggest that response to visual cues of risk may be impaired by CO2 and provide strong evidence that the multi-sensory effects of CO2 may stem from systematic effects at the neural level.