The Experts below are selected from a list of 96 Experts worldwide ranked by ideXlab platform
Adam Barnett - One of the best experts on this subject based on the ideXlab platform.
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Long-Term Changes in Species Composition and Relative Abundances of Sharks at a Provisioning Site
2016Co-Authors: Juerg M. Brunnschweiler, Kátya G. Abrantes, Adam BarnettAbstract:Diving with Sharks, often in combination with food baiting/provisioning, has become an important product of today’s recreational dive industry. Whereas the effects baiting/provisioning has on the behaviour and abundance of individual Shark species are starting to become known, there is an almost complete lack of equivalent data from multi-species Shark diving sites. In this study, changes in species composition and relative abundances were determined at the Shark Reef Marine Reserve, a multi-species Shark feeding site in Fiji. Using direct observation sampling methods, eight species of Sharks (bull Shark Carcharhinus leucas, grey Reef Shark Carcharhinus amblyrhynchos, Whitetip Reef Shark Triaenodon obesus, blacktip Reef Shark Carcharhinus melanopterus, tawny nurse Shark Nebrius ferrugineus, silvertip Shark Carcharhinus albimarginatus, sicklefin lemon Shark Negaprion acutidens, and tiger Shark Galeocerdo cuvier) displayed inter-annual site fidelity between 2003 and 2012. Encounter rates and/or relative abundances of some species changed over time, overall resulting in more individuals (mostly C. leucas) of fewer species being encountered on average on Shark feeding dives at the end of the study period. Differences in Shark community composition between the years 2004–2006 and 2007–2012 were evident, mostly because N. ferrugineus, C. albimarginatus and N. acutidens were much more abundant in 2004–2006 and very rare in the period of 2007– 2012. Two explanations are offered for the observed changes in relative abundances over time, namely inter-specific interactions and operator-specific feeding protocols. Both, possibly in combination, are suggested to be importan
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Long-term changes in species composition and relative abundances of Sharks at a provisioning site.
PloS one, 2014Co-Authors: Juerg M. Brunnschweiler, Kátya G. Abrantes, Adam BarnettAbstract:Diving with Sharks, often in combination with food baiting/provisioning, has become an important product of today’s recreational dive industry. Whereas the effects baiting/provisioning has on the behaviour and abundance of individual Shark species are starting to become known, there is an almost complete lack of equivalent data from multi-species Shark diving sites. In this study, changes in species composition and relative abundances were determined at the Shark Reef Marine Reserve, a multi-species Shark feeding site in Fiji. Using direct observation sampling methods, eight species of Sharks (bull Shark Carcharhinus leucas, grey Reef Shark Carcharhinus amblyrhynchos, Whitetip Reef Shark Triaenodon obesus, blacktip Reef Shark Carcharhinus melanopterus, tawny nurse Shark Nebrius ferrugineus, silvertip Shark Carcharhinus albimarginatus, sicklefin lemon Shark Negaprion acutidens, and tiger Shark Galeocerdo cuvier) displayed inter-annual site fidelity between 2003 and 2012. Encounter rates and/or relative abundances of some species changed over time, overall resulting in more individuals (mostly C. leucas) of fewer species being encountered on average on Shark feeding dives at the end of the study period. Differences in Shark community composition between the years 2004–2006 and 2007–2012 were evident, mostly because N. ferrugineus, C. albimarginatus and N. acutidens were much more abundant in 2004–2006 and very rare in the period of 2007–2012. Two explanations are offered for the observed changes in relative abundances over time, namely inter-specific interactions and operator-specific feeding protocols. Both, possibly in combination, are suggested to be important determinants of species composition and encounter rates, and relative abundances at this Shark provisioning site in Fiji. This study, which includes the most species from a spatially confined Shark provisioning site to date, suggests that long-term provisioning may result in competitive exclusion among Shark species.
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Variation in depth of Whitetip Reef Sharks: does provisioning ecotourism change their behaviour?
Coral Reefs, 2011Co-Authors: Richard Fitzpatrick, Kátya G. Abrantes, Jamie Seymour, Adam BarnettAbstract:In the dive tourism industry, Shark provisioning has become increasingly popular in many places around the world. It is therefore important to determine the impacts that provisioning may have on Shark behaviour. In this study, eight adult Whitetip Reef Sharks Triaenodon obesus were tagged with time-depth recorders at Osprey Reef in the Coral Sea, Australia. Tags collected time and depth data every 30 s. The absolute change in depth over 5-min blocks was considered as a proxy for vertical activity level. Daily variations in vertical activity levels were analysed to determine the effects of time of day on Whitetip Reef Shark behaviour. This was done for days when dive boats were absent from the area, and for days when dive boats were present, conducting Shark provisioning. Vertical activity levels varied between day and night, and with the presence of boats. In natural conditions (no boats present), Sharks remained at more constant depths during the day, while at night animals continuously moved up and down the water column, showing that Whitetip Reef Sharks are nocturnally active. When boats were present, however, there were also long periods of vertical activity during the day. If resting periods during the day are important for energy budgets, then Shark provisioning may affect their health. So, if this behaviour alteration occurs frequently, e.g., daily, this has the potential to have significant negative effects on the animals’ metabolic rates, net energy gain and overall health, reproduction and fitness.
Nicholas M Whitney - One of the best experts on this subject based on the ideXlab platform.
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oceanic dispersal in a sedentary Reef Shark triaenodon obesus genetic evidence for extensive connectivity without a pelagic larval stage
Journal of Biogeography, 2012Co-Authors: Nicholas M Whitney, William D Robbins, Jennifer K. Schultz, Brian W Bowen, Kim N HollandAbstract:Aim: Most Reef fishes are site-attached, but can maintain a broad distribution through their highly dispersive larval stage. The Whitetip Reef Shark (Triaenodon obesus) is site-attached, yet maintains the largest Indo-Pacific distribution of any Reef Shark while lacking the larval stage of bony (teleost) fishes. Here we use mitochondrial DNA (mtDNA) sequence data to evaluate the enigma of the sedentary Reef Shark that maintains a distribution across two-thirds of the planet. Location: Tropical Pacific and Indian Oceans. Methods: We analysed 1025 base pairs of the mtDNA control region in 310 individuals from 25 locations across the Indian and Pacific Oceans. Phylogeographic and population genetic analyses were used to reveal the dispersal and recent evolutionary history of the species. Results: We resolved 15 mtDNA control region haplotypes, but two comprised 87% of the specimens and were detected at nearly every location. Similar to other Sharks, genetic diversity was low (h = 0.550 ± 0.0254 and π = 0.00213 ± 0.00131). Spatial analyses of genetic variation demonstrated strong isolation across the Indo-Pacific Barrier and between western and central Pacific locations. Pairwise ΦST comparisons indicated high connectivity among archipelagos of the central Pacific but isolation across short distances of contiguous habitat (Great Barrier Reef) and intermittent habitat (Hawaiian Archipelago). In the eastern Pacific only a single haplotype (the most common one in the central Pacific) was observed, indicating recent dispersal (or colonization) across the East Pacific Barrier. Main conclusions: The shallow haplotype network indicates recent expansion of modern populations within the last half million years from a common ancestor. Based on the distribution of mtDNA diversity, this began with an Indo-West Pacific centre of origin, with subsequent dispersal to the Central Pacific and East Pacific. Genetic differences between Indian and Pacific Ocean populations are consistent with Pleistocene closures of the Indo-Pacific Barrier associated with glacial cycles. Pairwise population comparisons reveal weak but significant isolation by distance, and notably do not indicate the high coastal connectivity observed in other Shark species. The finding of population structure among semi-contiguous habitats, but population connectivity among archipelagos, may indicate a previously unsuspected oceanic dispersal behaviour in Whitetip Reef Sharks.
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Movements, reproductive seasonality, and fisheries interactions in the Whitetip Reef Shark (Triaenodon obesus) from community-contributed photographs
Environmental Biology of Fishes, 2012Co-Authors: Nicholas M Whitney, Kim N Holland, Richard L. Pyle, Jessica T. BarczAbstract:Despite being a common apex-level predator on coral Reefs throughout the tropical Indo-Pacific, surprisingly little is known about Whitetip Reef Shark ( Triaenodon obesus ) movements and biology. This study used photo-identification from community-contributed photographs to reveal patterns in movements, reproductive biology, and fisheries interactions in this species that have not been previously revealed through more traditional methods. At least 178 individual Sharks were identified, and 26 movements were observed. These included movement distances of up to 26.4 km, movement rates of up to 3.27 km/day (9.8 km in 3 days), and movements that required the transit of a 140 m deep channel. Other animals showed high philopatry, being re-sighted at the same locality on multiple occasions (up to 13 sightings for one individual) over periods of up to 7 years. Females showed higher philopatry than males and were more likely than males to be found at shallow (
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movements reproductive seasonality and fisheries interactions in the Whitetip Reef Shark triaenodon obesus from community contributed photographs
Environmental Biology of Fishes, 2012Co-Authors: Nicholas M Whitney, Kim N Holland, Richard Pyle, Jessica T. BarczAbstract:Despite being a common apex-level predator on coral Reefs throughout the tropical Indo-Pacific, surprisingly little is known about Whitetip Reef Shark (Triaenodon obesus) movements and biology. This study used photo-identification from community-contributed photographs to reveal patterns in movements, reproductive biology, and fisheries interactions in this species that have not been previously revealed through more traditional methods. At least 178 individual Sharks were identified, and 26 movements were observed. These included movement distances of up to 26.4 km, movement rates of up to 3.27 km/day (9.8 km in 3 days), and movements that required the transit of a 140 m deep channel. Other animals showed high philopatry, being re-sighted at the same locality on multiple occasions (up to 13 sightings for one individual) over periods of up to 7 years. Females showed higher philopatry than males and were more likely than males to be found at shallow (<10 m depth) localities throughout the year. The proportion of male sightings at shallow localities was significantly higher in April and May than other months of the year, possibly due to males coming into the shallows to mate with females. A peak in sightings of late-term females followed by an abrupt decline suggests that pupping season is May into early June, and two females were observed pregnant in consecutive years despite evidence that the gestation period is approximately 1 year for this species. Nine percent of animals carried fishing tackle or exhibited jaw injuries associated with fishery interactions, with multiple individuals found dead after being hooked by fishers.
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Group courtship, mating behaviour and siphon sac function in the Whitetip Reef Shark, Triaenodon obesus
Animal Behaviour, 2004Co-Authors: Nicholas M Whitney, Harold L. Pratt, Jeffrey C. CarrierAbstract:We analysed video records of three mating events involving nine free-living Whitetip Reef Sharks in Cocos Islands, Costa Rica to examine reproductive behaviour in this species. We describe several behaviours never before documented in this species, and four behaviours never before documented in any elasmobranch. Here, we also present the first hypothesis for the function of the male's paired reproductive organs, the siphon sacs, to be based on observations of mating Sharks. We introduce terminology for three separate siphon sac structural components that are externally visible during courtship and mating in this species. Based on our analyses, as well as evidence from past mating studies, the siphon sacs in Whitetip Reef Sharks appear to be used to propel sperm into the female's reproductive tract, not for flushing the female's reproductive tract of sperm from previous males. We discuss the implications of ‘group courtship’, ‘siphon isthmus constriction’, ‘reverse thrusting’, ‘postrelease gaping’ and ‘noncopulatory ejaculation’.
Kim N Holland - One of the best experts on this subject based on the ideXlab platform.
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oceanic dispersal in a sedentary Reef Shark triaenodon obesus genetic evidence for extensive connectivity without a pelagic larval stage
Journal of Biogeography, 2012Co-Authors: Nicholas M Whitney, William D Robbins, Jennifer K. Schultz, Brian W Bowen, Kim N HollandAbstract:Aim: Most Reef fishes are site-attached, but can maintain a broad distribution through their highly dispersive larval stage. The Whitetip Reef Shark (Triaenodon obesus) is site-attached, yet maintains the largest Indo-Pacific distribution of any Reef Shark while lacking the larval stage of bony (teleost) fishes. Here we use mitochondrial DNA (mtDNA) sequence data to evaluate the enigma of the sedentary Reef Shark that maintains a distribution across two-thirds of the planet. Location: Tropical Pacific and Indian Oceans. Methods: We analysed 1025 base pairs of the mtDNA control region in 310 individuals from 25 locations across the Indian and Pacific Oceans. Phylogeographic and population genetic analyses were used to reveal the dispersal and recent evolutionary history of the species. Results: We resolved 15 mtDNA control region haplotypes, but two comprised 87% of the specimens and were detected at nearly every location. Similar to other Sharks, genetic diversity was low (h = 0.550 ± 0.0254 and π = 0.00213 ± 0.00131). Spatial analyses of genetic variation demonstrated strong isolation across the Indo-Pacific Barrier and between western and central Pacific locations. Pairwise ΦST comparisons indicated high connectivity among archipelagos of the central Pacific but isolation across short distances of contiguous habitat (Great Barrier Reef) and intermittent habitat (Hawaiian Archipelago). In the eastern Pacific only a single haplotype (the most common one in the central Pacific) was observed, indicating recent dispersal (or colonization) across the East Pacific Barrier. Main conclusions: The shallow haplotype network indicates recent expansion of modern populations within the last half million years from a common ancestor. Based on the distribution of mtDNA diversity, this began with an Indo-West Pacific centre of origin, with subsequent dispersal to the Central Pacific and East Pacific. Genetic differences between Indian and Pacific Ocean populations are consistent with Pleistocene closures of the Indo-Pacific Barrier associated with glacial cycles. Pairwise population comparisons reveal weak but significant isolation by distance, and notably do not indicate the high coastal connectivity observed in other Shark species. The finding of population structure among semi-contiguous habitats, but population connectivity among archipelagos, may indicate a previously unsuspected oceanic dispersal behaviour in Whitetip Reef Sharks.
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Movements, reproductive seasonality, and fisheries interactions in the Whitetip Reef Shark (Triaenodon obesus) from community-contributed photographs
Environmental Biology of Fishes, 2012Co-Authors: Nicholas M Whitney, Kim N Holland, Richard L. Pyle, Jessica T. BarczAbstract:Despite being a common apex-level predator on coral Reefs throughout the tropical Indo-Pacific, surprisingly little is known about Whitetip Reef Shark ( Triaenodon obesus ) movements and biology. This study used photo-identification from community-contributed photographs to reveal patterns in movements, reproductive biology, and fisheries interactions in this species that have not been previously revealed through more traditional methods. At least 178 individual Sharks were identified, and 26 movements were observed. These included movement distances of up to 26.4 km, movement rates of up to 3.27 km/day (9.8 km in 3 days), and movements that required the transit of a 140 m deep channel. Other animals showed high philopatry, being re-sighted at the same locality on multiple occasions (up to 13 sightings for one individual) over periods of up to 7 years. Females showed higher philopatry than males and were more likely than males to be found at shallow (
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movements reproductive seasonality and fisheries interactions in the Whitetip Reef Shark triaenodon obesus from community contributed photographs
Environmental Biology of Fishes, 2012Co-Authors: Nicholas M Whitney, Kim N Holland, Richard Pyle, Jessica T. BarczAbstract:Despite being a common apex-level predator on coral Reefs throughout the tropical Indo-Pacific, surprisingly little is known about Whitetip Reef Shark (Triaenodon obesus) movements and biology. This study used photo-identification from community-contributed photographs to reveal patterns in movements, reproductive biology, and fisheries interactions in this species that have not been previously revealed through more traditional methods. At least 178 individual Sharks were identified, and 26 movements were observed. These included movement distances of up to 26.4 km, movement rates of up to 3.27 km/day (9.8 km in 3 days), and movements that required the transit of a 140 m deep channel. Other animals showed high philopatry, being re-sighted at the same locality on multiple occasions (up to 13 sightings for one individual) over periods of up to 7 years. Females showed higher philopatry than males and were more likely than males to be found at shallow (<10 m depth) localities throughout the year. The proportion of male sightings at shallow localities was significantly higher in April and May than other months of the year, possibly due to males coming into the shallows to mate with females. A peak in sightings of late-term females followed by an abrupt decline suggests that pupping season is May into early June, and two females were observed pregnant in consecutive years despite evidence that the gestation period is approximately 1 year for this species. Nine percent of animals carried fishing tackle or exhibited jaw injuries associated with fishery interactions, with multiple individuals found dead after being hooked by fishers.
Michel Kulbicki - One of the best experts on this subject based on the ideXlab platform.
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Comparative phylogeography of the western Indian Ocean Reef fauna
Acta Oecologica, 2016Co-Authors: Philippe Borsa, Jean-dominique Durand, Wei-jen Chen, Nicolas Hubert, Delphine Muths, Gérard Mou-tham, Michel KulbickiAbstract:Assessing patterns of connectivity at the community and population levels is relevant to marine resource management and conservation. The present study reviews this issue with a focus on the western Indian Ocean (WIO) biogeographic province. This part of the Indian Ocean holds more species than expected from current models of global Reef fish species richness. In this study, checklists of Reef fish species were examined to determine levels of endemism in each of 10 biogeographic provinces of the Indian Ocean. Results showed that the number of endemic species was higher in the WIO than in any other region of the Indian Ocean. Endemic species from the WIO on the average had a larger body size than elsewhere in the tropical Indian Ocean. This suggests an effect of peripheral speciation, as previously documented in the Hawaiian Reef fish fauna, relative to other sites in the tropical western Pacific. To explore evolutionary dynamics of species across biogeographic provinces and infer mechanisms of speciation, we present and compare the results of phylogeographic surveys based on compilations of published and unpublished mitochondrialDNA sequences for 19 Indo-Pacific Reef-associated fishes (rainbow grouper Cephalopholis argus, scrawled butterflyfish Chaetodon meyeri, bluespot mullet Crenimugil sp. A, humbug damselfish Dascyllus abudafur/D. aruanus, areolate grouper Epinephelus areolatus, blacktip grouper E. fasciatus, honeycomb grouper E. merra, bluespotted cornetfish Fistularia commersonii, cleaner wrasse Labroides sp. 1, longface emperor Lethrinus sp. A, bluestripe snapper Lutjanus kasmira, unicornfishes Naso brevirosris, N. unicornis and N. vlamingii, blue-spotted maskray Neotrygon kuhlii, largescale mullet Planiliza macrolepis, common parrotfish Scarus psicattus, crescent grunter Terapon jarbua, Whitetip Reef Shark Triaenodon obesus) and three coastal Indo-West Pacific invertebrates (blue seastar Linckia laevigata, spiny lobster Panulirus homarus, small giant clam Tridacna maxima). Heterogeneous and often unbalanced sampling design, paucity of data in a number of cases, and among-species discrepancy in phylogeographic structure precluded any generalization regarding phylogeographic patterns. Nevertheless, the WIO might have been a source of haplotypes in some cases and it also harboured an endemic clade in at least one case. The present survey also highlighted likely cryptic species. This may eventually affect the accuracy of the current checklists of species, which form the basis of some of the recent advances in Indo-West Pacific marine ecology and biogeography.
Kátya G. Abrantes - One of the best experts on this subject based on the ideXlab platform.
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Long-term changes in species composition and relative abundances of Sharks at a provisioning site.
PloS one, 2014Co-Authors: Juerg M. Brunnschweiler, Kátya G. Abrantes, Adam BarnettAbstract:Diving with Sharks, often in combination with food baiting/provisioning, has become an important product of today’s recreational dive industry. Whereas the effects baiting/provisioning has on the behaviour and abundance of individual Shark species are starting to become known, there is an almost complete lack of equivalent data from multi-species Shark diving sites. In this study, changes in species composition and relative abundances were determined at the Shark Reef Marine Reserve, a multi-species Shark feeding site in Fiji. Using direct observation sampling methods, eight species of Sharks (bull Shark Carcharhinus leucas, grey Reef Shark Carcharhinus amblyrhynchos, Whitetip Reef Shark Triaenodon obesus, blacktip Reef Shark Carcharhinus melanopterus, tawny nurse Shark Nebrius ferrugineus, silvertip Shark Carcharhinus albimarginatus, sicklefin lemon Shark Negaprion acutidens, and tiger Shark Galeocerdo cuvier) displayed inter-annual site fidelity between 2003 and 2012. Encounter rates and/or relative abundances of some species changed over time, overall resulting in more individuals (mostly C. leucas) of fewer species being encountered on average on Shark feeding dives at the end of the study period. Differences in Shark community composition between the years 2004–2006 and 2007–2012 were evident, mostly because N. ferrugineus, C. albimarginatus and N. acutidens were much more abundant in 2004–2006 and very rare in the period of 2007–2012. Two explanations are offered for the observed changes in relative abundances over time, namely inter-specific interactions and operator-specific feeding protocols. Both, possibly in combination, are suggested to be important determinants of species composition and encounter rates, and relative abundances at this Shark provisioning site in Fiji. This study, which includes the most species from a spatially confined Shark provisioning site to date, suggests that long-term provisioning may result in competitive exclusion among Shark species.
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Variation in depth of Whitetip Reef Sharks: does provisioning ecotourism change their behaviour?
Coral Reefs, 2011Co-Authors: Richard Fitzpatrick, Kátya G. Abrantes, Jamie Seymour, Adam BarnettAbstract:In the dive tourism industry, Shark provisioning has become increasingly popular in many places around the world. It is therefore important to determine the impacts that provisioning may have on Shark behaviour. In this study, eight adult Whitetip Reef Sharks Triaenodon obesus were tagged with time-depth recorders at Osprey Reef in the Coral Sea, Australia. Tags collected time and depth data every 30 s. The absolute change in depth over 5-min blocks was considered as a proxy for vertical activity level. Daily variations in vertical activity levels were analysed to determine the effects of time of day on Whitetip Reef Shark behaviour. This was done for days when dive boats were absent from the area, and for days when dive boats were present, conducting Shark provisioning. Vertical activity levels varied between day and night, and with the presence of boats. In natural conditions (no boats present), Sharks remained at more constant depths during the day, while at night animals continuously moved up and down the water column, showing that Whitetip Reef Sharks are nocturnally active. When boats were present, however, there were also long periods of vertical activity during the day. If resting periods during the day are important for energy budgets, then Shark provisioning may affect their health. So, if this behaviour alteration occurs frequently, e.g., daily, this has the potential to have significant negative effects on the animals’ metabolic rates, net energy gain and overall health, reproduction and fitness.
