Both sharks and humans present a potentially lethal threat to mesopredatory fishes in coral reef systems, with implications for both population dynamics and the role of mesopredatory fishes in reef ...ecosystems. This study quantifies the antipredator behaviours mesopredatory fishes exhibit towards the presence of large coral reef carnivores and compares these behavioural responses to those elicited by the presence of snorkelers. Here, we used snorkelers and animated life-size models of the blacktip reef shark (Carcharhinus melanopterus) to simulate potential predatory threats to mesopredatory reef fishes (lethrinids, lutjanids, haemulids and serranids). The responses of these reef fishes to the models and the snorkelers were compared to those generated by three non-threatening controls (life-size models of a green turtle Chelonia mydas, a PVC-pipe an object control and a Perspex shape a second object control). A Remote Underwater Stereo-Video System (Stereo-RUV) recorded the approach of the different treatments and controls and allowed accurate measurement of Flight Initiation Distance (FID) and categorization of the type of flight response by fishes. We found that mesopredatory reef fishes had greater FIDs in response to the approach of threatening models (1402 ± 402-1533 ± 171 mm; mean ± SE) compared to the controls (706 ± 151-896 ± 8963 mm). There was no significant difference in FID of mesopredatory fishes between the shark model and the snorkeler, suggesting that these treatments provoked similar levels of predator avoidance behaviour. This has implications for researchers monitoring behaviour in situ or using underwater census as a technique to estimate the abundance of reef fishes. Our study suggests that, irrespective of the degree to which sharks actually consume these mesopredatory reef fishes, they still elicit a predictable and consistent antipredator response that has the potential to create risk effects.
► We conducted surveys to estimate the economic value of shark-diving tourism in Palau. ► The shark-diving industry generated US$18 million to the economy of Palau annually. ► This industry generated ...US$1.2 million per year in salaries to the local community. ► Shark-diving contributed with US$1.5 million in taxes to the Government annually. ► Shark-diving generated 8% of the GDP and 14% of the business tax revenues annually.
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.
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’ (<570
Hz)-frequency components of reef noise and compared these catches with those from control ‘silent’ traps. Of the seven families represented by >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.
Whale sharks (Rhincodon typus Smith) aggregate seasonally (March–June) to feed in coastal waters off Ningaloo Reef, Western Australia. Pop-up archival tags were attached to 19 individuals (total ...lengths 4.5–11.0 m) at this location in early May of 2003 and 2004 to examine their horizontal and vertical movements. The long-term movement patterns of six whale sharks were documented, all of which travelled northeast into the Indian Ocean after departing Ningaloo Reef. They used both inshore and offshore habitats and made extensive vertical movements, occasionally to a depth of at least 980 m. Frequent up-and-down movements, diel vertical migration, and crepuscular descents were evident in the depth records. The sharks experienced ambient temperatures ranging between 4.2 and 28.7°C and encountered gradients of up to 20.8°C on dives.
Telemetry is a key, widely used tool to understand marine megafauna distribution, habitat use, behavior, and physiology; however, a critical question remains: “How many animals should be tracked to ...acquire meaningful data sets?” This question has wide-ranging implications including considerations of statistical power, animal ethics, logistics, and cost. While power analyses can inform sample sizes needed for statistical significance, they require some initial data inputs that are often unavailable. To inform the planning of telemetry and biologging studies of marine megafauna where few or no data are available or where resources are limited, we reviewed the types of information that have been obtained in previously published studies using different sample sizes. We considered sample sizes from one to >100 individuals and synthesized empirical findings, detailing the information that can be gathered with increasing sample sizes. We complement this review with simulations, using real data, to show the impact of sample size when trying to address various research questions in movement ecology of marine megafauna. We also highlight the value of collaborative, synthetic studies to enhance sample sizes and broaden the range, scale, and scope of questions that can be answered.
Replenishment of benthic marine populations typically involves "settlement" from pelagic larval to benthic juvenile habitats. Mortality during this transition has been unknown because of the ...difficulty of measuring propagule supply in open water. For three weeks, we compared the nocturnal passage of presettlement fishes across the barrier reef encircling Moorea Island (French Polynesia) with the abundance of benthic recruits in the back-reef lagoon on the following morning. During this time, >40,000 presettlement unicornfish, Naso unicornis entered our study area of ∼ 1 km2with half arriving on just two nights. Using coupled Beverton-Holt functions to describe the decay of each cohort, we were able to predict the daily abundance of recruits and their final age structure from the presettlement inputs. The best model estimated that ∼ 61% of the potential settlers were lost between their nocturnal arrival and the following morning, independent of cohort size. Postsettlement mortality was density dependent, varying between 9% and 20% per day. We attribute all mortality to predation and suggest that high risk associated with settlement has shaped colonization strategies. Because fishing targets the survivors of this population bottleneck, aquarium fisheries may be more sustainable when sourced from pelagic juveniles.
In-water viewing of sharks by tourists has become a popular and lucrative industry. There is some concern that interactions with tourists with ecotourism operations might harm sharks through ...disruption of behaviours. Here, we analysed five years of whale shark (Rhincodon typus) encounter data by an ecotourism industry at Ningaloo Reef, Western Australia, to assess the impact of ecotourism interactions on shark visitation, within the context of the biological and physical oceanography of the region. Our data base consisted of 2823 encounter records for 951 individual whale sharks collected by ecotourism operators between 2007 and 2011. We found that total encounters per whale shark and encounters per boat trip increased through time. On average, whale sharks re-encountered in subsequent years were encountered earlier, stayed longer and tended to be encountered more often within a season than sharks that were only encountered in a single year. Sequential comparisons between years did not show any patterns consistent with disturbance and the rate of departure of whale sharks from the aggregation was negatively correlated to the number of operator trips. Overall, our analysis of this multi-year data base found no evidence that interactions with tourists affected the likelihood of whale shark re-encounters and that instead, physical and biological environmental factors had a far greater influence on whale shark visitation rates. Our approach provides a template for assessing the effects of ecotourism interactions and environmental factors on the visitation patterns of marine megafauna over multiple years.
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.
We developed predictive models of coral reef fish species richness and abundance that account for both broad-scale environmental gradients and fine-scale biotic processes, such as dispersal, and we ...compared the importance of absolute geographical location (i.e. geographical coordinates) versus relative geographical location (i.e. distance to domain boundaries). Great Barrier Reef, Australia. Four annual surveys of coral reef fishes were combined with a 0.01°-resolution grid of environmental variables including depth, sea surface temperature, salinity and nutrient concentrations. A principal component-based method was developed to select candidate predictors from a large number of correlated variables. Generalized linear mixed-effects models (GLMMs) were used to gauge the respective importance of the different spatial and environmental predictors. An error covariance matrix was included in the models to account for spatial autocorrelation. (1) Relative geographical descriptors, represented by distances to the coast and to the barrier reef, provided the highest-ranked single model of species richness and explained up to 36.8% of its deviance. (2) Accounting for spatial autocorrelation doubled the deviance in abundance explained to 71.9%. Sea surface temperature, salinity and nitrate concentrations were also important predictors of abundance. Spatially explicit predictions of species richness and abundance were robust to variation in the spatial scale considered during model calibration. This study demonstrates that distance-to-domain boundaries (i.e. relative geographical location) can offer an ecologically relevant alternative to geographical coordinates (i.e. absolute geographical location) when predicting biodiversity patterns, providing a proxy for multivariate and complex environmental processes that are often difficult or expensive to estimate.
Large pelagic vertebrates pose special conservation challenges because their movements generally exceed the boundaries of any single jurisdiction. To assess the population structure of whale sharks ...(Rhincodon typus), we sequenced complete mitochondrial DNA control regions from individuals collected across a global distribution. We observed 51 single site polymorphisms and 8 regions with indels comprising 44 haplotypes in 70 individuals, with high haplotype (h = 0.974 ± 0.008) and nucleotide diversity (π = 0.011 ± 0.006). The control region has the largest length variation yet reported for an elasmobranch (1143-1332 bp). Phylogenetic analyses reveal no geographical clustering of lineages and the most common haplotype was distributed globally. The absence of population structure across the Indian and Pacific basins indicates that oceanic expanses and land barriers in Southeast Asia are not impediments to whale shark dispersal. We did, however, find significant haplotype frequency differences (amova, FST = 0.107, P < 0.001) principally between the Atlantic and Indo-Pacific populations. In contrast to other recent surveys of globally distributed sharks, we find much less population subdivision and no evidence for cryptic evolutionary partitions. Discovery of the mating and pupping areas of whale sharks is key to further population genetic studies. The global pattern of shared haplotypes in whale sharks provides a compelling argument for development of broad international approaches for management and conservation of Earth's largest fish.
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