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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.

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.

Shark-diving tourism is a fast-growing industry that provides socio-economic benefits to local communities. This study estimated the economic contribution of the shark-diving tourism in the Maldives by using surveys with dive tourists and dive operators. Direct business revenue from shark divers was estimated to be US$14.4 million. Revenues to local businesses associated with travel expenses of shark divers were estimated to be US$51.4 million. Further economic benefits from shark-diving occurred in form of annual business tax revenues of US$7.2 million and annual salaries to employees working in the diving industry of US$4.1 million. These values were compared with the business revenues from shark-diving in the Maldives in 1992 to assess how the shark-diving industry has changed over time. The results of this study indicate that the business revenues of this industry have almost doubled (when inflation adjusted) over the last 24 years confirming its economic growth and importance for the Maldives. Effective management of shark dive operations is crucial for maintaining the value and sustainability of this tourism industry to improve ongoing conservation efforts for shark populations.

Shark-diving tourism provides important economic benefits to the Maldives. We examine the link between shark conservation actions and economic returns from diving tourism. A combined travel cost and contingent behaviour approach is used to estimate the dive trip demand under different management scenarios. Our results show that increasing shark populations could increase dive-trip demand by 15%, raising dive tourists’ welfare by US$58 million annually. This could result in annual economic benefits for the dive-tourism industry of >US$6 million. Conversely, in scenarios where shark populations decline, where dive tourists observe illegal fishing, or if dive operators lack engagement in shark conservation, dive trip demand could decrease by up to 56%. This decline causes economic losses of more than US$24 million annually to the dive tourism industry. These results highlight the dependence of the shark-diving industry on the creation and enforcement of appropriate management regimes for shark conservation.

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.

This study estimated the economic value of the shark-diving industry in Semporna, the most popular diving destination of Malaysia, by surveying the expenditures of diving tourists and dive operators through the region. A willingness-to-pay survey was also used to estimate the potential of the industry as a financing mechanism for enforcement and management of a hypothetical Marine Protected Area (MPA) to conserve shark populations. The study showed that in 2012, shark-diving tourism provided direct revenues in excess of USD 9.8 million to the Semporna region. These economic benefits had a flow-on effect, generating more than USD 2 million in direct taxes to the government and USD 1.4 million in salaries to the community. A contingent valuation analysis indicated that implementation of a fee paid by divers could generate over USD 2 million for management and enforcement of the MPA each year. These findings suggest that shark diving is an important contributor to the economy of the Semporna region that could be used as a mechanism to assist financial resourcing for management and conservation strategies.

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.

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.

Many marine fish populations have declined due to the individual or cumulative impacts of increasing water temperatures, ocean acidification, overfishing and other human-induced impacts such as land run-off, dredging and habitat alteration. Some solutions may be offered by ecosystem-based fisheries and conservation management. However, understanding their effectiveness relies on the availability of good quality data on the size distributions and abundance of fish populations and assemblages, collected at appropriate temporal and spatial scales. Since the early 2000s, baited remote underwater video systems (BRUVs) have become a popular tool for collecting data on fish assemblages across a range of depths and habitats. In Australia, this technique has been adopted by many different agencies and institutions, creating a unique opportunity to compile a continental-scale synthesis of fish data using a standardised sampling technique. Key Australian researchers and managers were invited to contribute to a synthesis workshop on baited underwater video in Albany, Western Australia between the 4th and 8th of February 2018. Data from 19,939 BRUVs deployments, collected between 2000 and 2017 around Australia, were compiled using GlobalArchive (globalarchive.org). The workshop identified and prioritised several key research themes that would contribute to the conservation and sustainable management of focal species and broad assemblages. Our goal is to describe where and when the data were collected, the type of equipment used and how the imagery was analysed. We also discuss the types of questions that can be addressed by analysing these standardised datasets and the potential benefits to conservation and fisheries management.

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.

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.

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.

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.

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.

Long-term vital rate and life-history data essential for sustainable harvest management are rare in tropical fisheries. Two commercially important shark species, Australian blacktip ( Carcharhinus tilstoni ) and spot-tail ( C. sorrah ) sharks in northern Australia have changed in size and population status over the last 25 years. These populations were exploited heavily from the early 1970s to the mid-1980s by foreign fishers, and since then have been harvested by a relatively small domestic fishery. We examined the differences in fork length of these species caught in 1983–1985 and 2002–2006 using Bayesian forms of generalised linear and mixed-effects models. We found clear regional differences and changes in size over time. For blacktips, sharks from the Gulf of Carpentaria have become smaller, and those from the western Northern Territory, larger over time. For spot-tail sharks, average size increased from the 1980s in the Gulf of Carpentaria, but not in the western Northern Territory. On average, sharks from the Gulf of Carpentaria were larger than those on the west coast of the Northern Territory, and females were larger than males. We suggest that changes over time and between regions in the size of spot-tail sharks are most likely due to over-exploitation in the past and subsequent recovery of populations. We discuss the uncertainty in trends for blacktip sharks in relation to fishing effort, availability of resources and species identification errors.

Arguments for conservation of sharks based on their role in the maintenance of healthy marine ecosystems have failed to halt the worldwide decline in populations. Instead, the value of sharks as a fishery commodity has severely reduced the abundance of these animals. Conservation may be assisted by the development of an alternative approach that emphasizes the economic value of sharks as a non-harvested resource. Our study quantifies the value of a tourism industry based on shark diving. Using data collected from surveys, as well as government statistics, we show that shark diving is a major contributor to the economy of Palau, generating US$18 million per year and accounting for approximately 8% of the gross domestic product of the country. Annually, shark diving was responsible for the disbursement of US$1.2 million in salaries to the local community, and generated US$1.5 million in taxes to the government. If the population of approximately 100 sharks that interact with tourists at popular dive sites was harvested by fishers, their economic value would be at most US$10 800, a fraction of the worth of these animals as a non-consumptive resource. Fishers earn more selling fish for consumption by shark divers than they would gain by catching sharks. Shark diving provides an attractive economic alternative to shark fishing, with distribution of revenues benefiting several sectors of the economy, stimulating the development and generating high revenues to the government, while ensuring the ecological sustainability of shark populations.

Seven whale sharks were tracked using satellite-linked tags from Ningaloo Reef, off northern Western Australia, following tagging in April and June 2002 and April–May 2005. We investigated how the movements of those whale shark tracks were influenced by geostrophic surface currents during sequential one-week periods by using a passive diffusion model parameterised with observed starting locations of the sharks and weekly maps of surface current velocity and direction (derived from altimetry). We compared the outputs from the passive diffusion model and maps of chlorophyll-a concentration (SeaWiFs/MODIS) and with the actual tracks of the sharks using GIS and generalized linear mixed-effects models (GLMM). The GLMM indicated very little support for passive diffusion with sea-surface ocean currents influencing whale shark distributions in the north eastern Indian Ocean. Moreover, the sharks' movements correlated only weakly with the spatial distribution of sea-surface chlorophyll-a concentrations. The seven whale sharks had average swimming speeds comparable with those recorded in other satellite tracking studies of this species. Swimming speeds of the seven sharks were similar to those reported in previous studies and up to three times greater than the maximum sea-surface current velocities that the sharks encountered while traversing into lower southerly latitudes (moving northward towards the equator). Our results indicate that whale sharks departing from Ningaloo travel actively and independently of near-surface currents where they spend most of their time despite additional metabolic costs of this behaviour.

Trade-offs between the costs and benefits of growth are thought to be mediated by behaviour, whereby rapid growth is associated with greater predation mortality because of increased foraging effort. We tested this hypothesis by collecting young Pomacentrus amboinensis using light traps and settling them onto patch reefs where their behaviour and survivorship were monitored for 24 h. One month later, individuals of the same cohort were collected from shallow reefs and released onto patch reefs where their behaviour and survivorship were monitored for 6 days. At settlement young fish suffered high (60% in 24 h) mortality that preferentially removed larger, faster-growing individuals. However, we could find no evidence that foraging behaviour contributed to this selective mortality. In contrast, 1 month later the same cohort underwent negative size-selective mortality where the smallest, slower-growing fish were preferentially removed by predators. Larger fish spent more time foraging, were more aggressive, swam greater distances and chased more fish than smaller individuals. Thus, consistent individual differences in behaviour contributed to patterns of mortality, but in a way that involved no apparent trade-off with growth. For P. amboinensis, consistent variation in growth may be maintained by spatial and temporal differences in the selective regime within the reef environment.

Seasonal observations of whale shark abundance recorded by ecotourist operators at Ningaloo Reef, Western Australia from 1999 to 2004 were compared with weekly regional and global oceanographic and atmospheric variables, including average sea surface temperatures, along-shelf wind shear, sea level and the Southern Oscillation Index (SOI). Estimates of these physical variables were derived from either ground-based data or from remote sensing instruments. A generalised linear mixed-effects modelling (GLMM) approach with random sampling and model simulation was used to determine the relationships between the number of whale sharks and all model variants of the environmental parameters, using information-theoretic weights of evidence to rank models. SOI and wind shear had the most support for explaining the deviance in weekly whale shark abundance at Ningaloo Reef during a season. The SOI and wind shear variables positively influenced whale shark abundance such that more sharks were sighted when the Southern Oscillation was stronger and along-shelf winds were increasingly prevalent. This may reflect changes in the strength of oceanographic processes such as the Leeuwin Current (in response to the Southern Oscillation) and wind/current driven upwelling which may affect the abundance of whale sharks transported to the region and/or the availability of their prey by driving productivity changes.

Multiple internal and external tagging experiments tested the applicability of five back-calculation models (Biological Intercept, Modified-Fry, Body Proportional Hypothesis, Time-Varying Growth, and an Age-Effects model) as predictors of individual growth trajectories of two marine cleaning gobies, Elacatinus evelynae and E. prochilos, that were raised in aquaria under conditions that resulted in variable growth. Mixed-effect model analyses of longitudinal records of otoliths and somatic growth collected at the individual level revealed that E. evelynae and E. prochilos produced daily increments on their otoliths for up to two months post-settlement and that the Modified-Fry model provided the most accurate size-at-age estimates despite the presence of age, growth and time-varying growth effects in the dataset. Very large errors in predicted size were produced by the Age-Effects model. The four other back-calculation models all provided slightly biased estimates of back-calculated size-at-age, with the Modified-Fry model providing the least biased estimates. Regardless of bias, both experimental and theoretical evidence indicated that back-calculated size was a better proxy of fish length than otoliths radius. Relationships between fish length and otoliths radius were allometric at the level of individuals, which explained why the Modified-Fry model performed better. However, this allometry was undetectable at the population level. This study represents the first attempt to validate modern back-calculation models using longitudinal data collected and analysed at the individual level. Our results suggest the use of the Modified-Fry model as a conservative approach in routine back-calculations of fish size at age from otoliths.

Aerial surveys have been used to estimate population abundance of both terrestrial and marine species; in the marine environment this has largely been used for air-breathing species that spend time regularly at the surface. Whale sharks spend a large proportion of their time close to the surface and so are amenable to aerial survey techniques. This study presents the results of six years of synoptic aerial belt-surveys done nearly daily during the peak whale shark season around the island of Mahe, Seychelles. A total of 580 survey flights were flown providing 699.7 hours of survey record. A seasonal peak of shark sightings per hour was recorded in September or October in most years with the maximum on a single survey of 28.4 h- 1 in October 2006. The aerial survey data were used to generate an estimate of relative population abundance indicating that highest mean annual relative population estimate was also in 2006, with an estimate of 38, while the lowest mean estimate was 11 in 2004. These estimates were then compared to weekly capture-mark-recapture estimates of abundance based on unique individual identification data. The results indicate that the use of aerial survey data alone may give an acceptable indication of instantaneous relative population abundance but further refinement is necessary to estimate absolute regional abundance.

Over-exploitation of whale sharks threatens the future of these wide-ranging pelagic fish. A long-term continuous record (4436 sightings) from a large aggregation (300–500 resident individuals) of whale sharks at Ningaloo Reef, Western Australia shows that mean shark length declined linearly by nearly 2.0 m and relative abundance measured from ecotourism sightings (corrected for variation in search effort and environmental stochasticity) has fallen by approximately 40% over the last decade. This population-level result confirms previous predictions of population decline based on projection models parameterised using mark-recapture estimates of survival. The majority of these changes are driven by reductions in the number of large individuals in the population. Phenomenological time series models support a deterministic (extrinsic) decline in large females, although there was some evidence for density dependence in large males. These reductions have occurred despite the total protection of whale sharks in Australian waters. As this species is highly migratory, the rapid change in population composition over a decade (

The importance of the acoustic cuescape is often overlooked in studies of animal orientation. Recent studies have shown that reef noise affects the behaviour and orientation of settlement-stage coral reef fish. This response may simply facilitate orientation to reefs; alternatively, acoustic habitat cues could also facilitate the remote selection of suitable settlement habitats. To test which components of reef noise evoke behavioural responses in larval fish, we used light traps to measure the responses of a diverse range of settlement-stage fish to the filtered ‘high’ (570–2000 Hz)- and ‘low’ ( 10 individuals, four (Pomacentridae, Apogonidae, Lethrinidae and Gobiidae) were caught in significantly greater numbers in the high-frequency traps than either the low-frequency or the silent traps. The Syngnathidae preferred high- to low-frequency traps, while the Blenniidae preferred high-frequency to silent traps. Only the Siganidae showed no preference between any of the sound treatments. Although some species-level variation in response was found, the general trend was a preference for high-frequency traps. This study suggests that most settlement-stage fish select the higher-frequency audible component of reef noise, which is produced mainly by marine invertebrates, as a means of selectively orienting towards suitable settlement habitats. The results highlight potential impacts of anthropogenic noise pollution and habitat modification in affecting the natural behaviour of reef fish at a critical stage in their life history.

Recently, Roff et al. reviewed the ecological roles of sharks as predators on coral reefs [1], with a focus on evidence that the loss of reef sharks drives trophic cascades in these ecosystems. They concluded that there is little support for the idea that sharks have a major structuring influence on the abundance and biomass of fishes at lower trophic levels of food webs or that they have an indirect influence on the cover of live coral and, thus, measures of reef ‘health’. However, a major issue with their approach is that it primarily reviews evidence from correlative, observational studies that compare trophic structures of fishes on reefs with and without sharks.

We describe the spatial and temporal dynamics of macrozooplankton on the southern North West Shelf (NWS) of Australia over two consecutive summers (1997/1998 and 1998/1999). Sampling was conducted using submersible light traps, deployed at the surface and at depth, along one cross-shelf transect in 1997/1998, and along two cross-shelf transects and one long-shore transect in 1998/1999. Our results revealed large inter-annual changes in macrozooplankton assemblages during the two summers. An upwelling regime associated with El Nino conditions prevailed during the first summer, resulting in high chlorophyll concentrations and an abundance of both meso- and macrozooplankton. During this time, there were distinct inshore and offshore macrozooplankton assemblages that reflected an abrupt transition from upwelling-enriched shelf waters to oligotrophic oceanic waters. In contrast, the second summer was characterised by a downwelling regime associated with La Nina conditions that resulted in low chlorophyll concentrations and decreased abundances of meso- and macrozooplankton. The lack of upwelling activity weakened horizontal gradients in macrozooplankton assemblages so that differences between surface and deep assemblages were more pronounced. Catches in light traps were dominated by hyperiid amphipods during the first summer and by the neritic euphausiid Pseudeuphausia latifrons during the second. There was little within-season change in macrozooplankton assemblages during both summers, and only weak relationships were found between the environmental parameters and the distribution of individual macrozooplankton taxa.

A pronounced shift in water column characteristics and in the composition of plankton communities was observed following the passage of Tropical Cyclone Tiffany along the margin of the southern Northwest Shelf, Australia in January 1998. Satellite-derived images of sea surface temperature, meteorological and hydrographic data indicate a southward movement of shelf waters into the study area near North West Cape (21°46′S). Changes in water mass temperature and salinity characteristics also occurred as a result of local heating and evaporation. Local in situ growth was likely to have caused increases in micro-phytoplankton abundance, biomass and primary production on the shelf. A diverse, copepod-dominated shelf mesozooplankton community changed to a less diverse assemblage dominated by copepods usually found in shallow nearshore habitats. Post-cyclone larval fish catches included families absent or rare in pre-cyclone samples. In the case of copepods and larval fish, southward transport of water masses along the shelf was most likely to have caused the observed changes. Long-shore water transport forced by cyclonic winds may be a recurrent, but episodic mechanism of planktonic dispersal on the North West Shelf.

Australian Institute of Marine Science, The UWA Oceans Institute (MO96), 35 Stirling Hwy, Crawley, WA 6009, Australia b School of Animal Biology, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia Centre for Environmental Economics and Policy, School of Agricultural and Resource Economics (M089), The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia Centre for Marine Futures (Oceans Institute), Oceans Institute, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia

a GIS and Remote Sensing Group, Charles Darwin University, Darwin, Northern Territory 0909, Australia b Australian Institute of Marine Science, P.O. Box 40197, Casuarina MC, Northern Territory 0811, Australia c Hubbs-SeaWorld Research Institute, 2595 Ingraham Street, San Diego, CA 92109, USA d Hopkins Marine Laboratory, Stanford University, 120 Oceanview Blvd., Pacific Grove, CA 93950, USA e National Marine Fisheries Service, Pacific Islands Fisheries Science Center, Honolulu, HI, USA f CSIRO Marine and Atmospheric Research, G.P.O. Box 1538, Hobart, Tasmania 7001, Australia g The Environment Institute and School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia h South Australian Research and Development Institute, P.O. Box 120, Henley Beach, South Australia 5022, Australia