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Williamson MJ, Tebbs EJ, Curnick DJ, Ferretti F, Carlisle AB, Chapple TK, Schallert RJ, Tickler DM, Block BA, Jacoby DMP. Environmental stress reduces shark residency to coral reefs. Commun Biol 2024; 7:1018. [PMID: 39251811 PMCID: PMC11385207 DOI: 10.1038/s42003-024-06707-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Accepted: 08/08/2024] [Indexed: 09/11/2024] Open
Abstract
Coral reef ecosystems are highly threatened and can be extremely sensitive to the effects of climate change. Multiple shark species rely on coral reefs as important habitat and, as such, play a number of significant ecological roles in these ecosystems. How environmental stress impacts routine, site-attached reef shark behavior, remains relatively unexplored. Here, we combine 8 years of acoustic tracking data (2013-2020) from grey reef sharks resident to the remote coral reefs of the Chagos Archipelago in the Central Indian Ocean, with a satellite-based index of coral reef environmental stress exposure. We show that on average across the region, increased stress on the reefs significantly reduces grey reef shark residency, promoting more diffuse space use and increasing time away from shallow forereefs. Importantly, this impact has a lagged effect for up to 16 months. This may have important physiological and conservation consequences for reef sharks, as well as broader implications for reef ecosystem functioning. As climate change is predicted to increase environmental stress on coral reef ecosystems, understanding how site-attached predators respond to stress will be crucial for forecasting the functional significance of altering predator behavior and the potential impacts on conservation for both reef sharks and coral reefs themselves.
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Affiliation(s)
- Michael J Williamson
- Institute of Zoology, Zoological Society of London, London, UK.
- Department of Geography, King's College London, London, UK.
- Department of Genetics, Evolution and Environment, University College London, London, UK.
| | - Emma J Tebbs
- Department of Geography, King's College London, London, UK
| | - David J Curnick
- Institute of Zoology, Zoological Society of London, London, UK
| | - Francesco Ferretti
- Department of Fish and Wildlife Conservation, Virginia Tech, Blacksburg, VA, USA
| | - Aaron B Carlisle
- School of Marine Science and Policy, University of Delaware, Lewes, DE, USA
| | - Taylor K Chapple
- Hatfield Marine Science Center, Oregon State University, Newport, OR, USA
| | | | - David M Tickler
- Marine Futures Lab, School of Biological Sciences, University of Western Australia, Perth, WA, Australia
| | - Barbara A Block
- Hopkins Marine Station, Stanford University, Pacific Grove, CA, USA
| | - David M P Jacoby
- Institute of Zoology, Zoological Society of London, London, UK.
- Lancaster Environment Centre, Lancaster University, Lancaster, UK.
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2
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Gayford JH, Sternes PC. The origins and drivers of sexual size dimorphism in sharks. Ecol Evol 2024; 14:e11163. [PMID: 38500855 PMCID: PMC10944705 DOI: 10.1002/ece3.11163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Accepted: 03/05/2024] [Indexed: 03/20/2024] Open
Abstract
While sexual size dimorphism (SSD) is abundant in nature, there is huge variation in both the intensity and direction of SSD. SSD results from a combination of sexual selection for large male size, fecundity selection for large female size and ecological selection for either. In most vertebrates, it is variation in the intensity of male-male competition that primarily underlies variation in SSD. In this study, we test four hypotheses regarding the adaptive value of SSD in sharks-considering the potential for each of fecundity, sexual, ecological selection and reproductive mode as the primary driver of variation in SSD between species. We also estimate past macroevolutionary shifts in SSD direction/intensity through shark phylogeny. We were unable to find evidence of significant SSD in early sharks and hypothesise that SSD is a derived state in this clade, that has evolved independently of SSD observed in other vertebrates. Moreover, there is no significant relationship between SSD and fecundity, testes mass or oceanic depth in sharks. However, there is evidence to support previous speculation that reproductive mode is an important determinant of interspecific variation in SSD in sharks. This is significant as in most vertebrates sexual selection is thought to be the primary driver of SSD trends, with evidence for the role of fecundity selection in other clades being inconsistent at best. While the phylogenetic distribution of SSD among sharks is superficially similar to that observed in other vertebrate clades, the relative importance of selective pressures underlying its evolution appears to differ.
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Affiliation(s)
- Joel H. Gayford
- Department of Life SciencesSilwood Park Campus, Imperial College LondonLondonUK
- Shark MeasurementsLondonUK
| | - Phillip C. Sternes
- Shark MeasurementsLondonUK
- Department of Evolution, Ecology and Organismal BiologyUniversity of CaliforniaRiversideCaliforniaUSA
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Le Croizier G, Lorrain A, Hoyos-Padilla M, Ketchum JT, Amezcua-Martínez F, Le Loc'h F, Munaron JM, Schaal G, Point D. Do marine protected areas influence mercury exposure? Insights from a shark community in the tropical Northeast Pacific. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2023; 336:122352. [PMID: 37562525 DOI: 10.1016/j.envpol.2023.122352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 07/12/2023] [Accepted: 08/08/2023] [Indexed: 08/12/2023]
Abstract
Biomass depletion caused by overfishing is likely to alter the structure of food webs and impact mercury transfer to marine predators. Although marine protected areas (MPAs) are spared from fishing pressure, their influence on biota mercury levels is poorly understood. Here, we used carbon and nitrogen stable isotope compositions as well as mercury concentrations in fin clips to characterize foraging habitat and mercury exposure of a shark community composed of migratory and resident species of the Revillagigedo archipelago, an offshore MPA in the Northeast Pacific off Mexico. We found that the probability of finding migratory sharks in the isotopic niche of Revillagigedo-resident sharks was low, likely reflecting the use of habitats outside the archipelago by highly mobile species. Community-wide variations in mercury were primarily explained by shark length, revealing that bioaccumulation was the main driver of Hg concentrations. We failed to detect a clear effect of foraging habitat on shark mercury exposure, which may be related to migratory species using both exploited and protected areas when moving outside the Revillagigedo MPA. More similar studies on the potential mitigation of Hg contamination by MPAs are needed in the future if fishing pressure increases to satisfy the growing global human population.
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Affiliation(s)
- Gaël Le Croizier
- Instituto de Ciencias Del Mar y Limnología, Universidad Nacional Autónoma de México, Av. Joel Montes Camarena S/N, Mazatlán, Sin, 82040, Mexico.
| | - Anne Lorrain
- Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280, Plouzané, France
| | - Mauricio Hoyos-Padilla
- Pelagios-Kakunjá A.C, Sinaloa 1540, Col. Las Garzas, C.P. 23070, La Paz, B.C.S., Mexico; Fins Attached: Marine Research and Conservation, 19675 Still Glen Drive, Colorado Springs, CO 80908, USA
| | - James T Ketchum
- Pelagios-Kakunjá A.C, Sinaloa 1540, Col. Las Garzas, C.P. 23070, La Paz, B.C.S., Mexico; MigraMar, Bodega Bay, CA, USA; Centro de Investigaciones Biológicas Noroeste (CIBNOR), La Paz, B.C.S., Mexico
| | - Felipe Amezcua-Martínez
- Instituto de Ciencias Del Mar y Limnología, Universidad Nacional Autónoma de México, Av. Joel Montes Camarena S/N, Mazatlán, Sin, 82040, Mexico
| | | | | | - Gauthier Schaal
- Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280, Plouzané, France
| | - David Point
- UMR Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), 14 Avenue Edouard Belin, 31400, Toulouse, France
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Shen Y, Gong Y, Wu F, Li Y. Retrospective stable isotopes of vertebrae reveal sexual ontogenetic patterns and trophic ecology in oceanic whitetip shark, Carcharhinus longimanus. Ecol Evol 2022; 12:e8452. [PMID: 35127009 PMCID: PMC8796903 DOI: 10.1002/ece3.8452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 11/21/2021] [Accepted: 11/29/2021] [Indexed: 11/25/2022] Open
Abstract
There is a common phenomenon in nature whereby some animals have differences in their ontogenetic changes in dietary preferences between sexes, especially apex predators. These reflect changes in the needs of development during their lifetimes. Apex predators potentially have diverse dietary niches and a large impact on the trophic dynamics within ecosystems. However, the difference in life history between males and females often leads to increased difficulty in management and conservation. In this study, 25 oceanic whitetip sharks, Carcharhinus longimanus, were collected from the central and eastern tropical Pacific. Retrospective stable isotope analysis of vertebrae was used to evaluate the potential ontogenetic differences in feeding habits and niche width between sexes. Results showed that C. longimanus had a wide range of δ13C values (-18.1 to -12.3‰) and δ15N values (8.9-14.8‰). However, males and females had similar trophic positions with large niche overlap at similar growth stages. Both sexes had increasing δ13C values but relatively constant δ15N values along the vertebrae. These results indicated that male and female C. longimanus may share similar feeding strategies and movement patterns. The results presented in this study enhance our understanding of sexual ontogenetic patterns and ecological role of C. longimanus and highlighted the applicability of vertebrae for characterizing shark life-history traits.
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Affiliation(s)
- Yongfu Shen
- College of Marine SciencesShanghai Ocean UniversityShanghaiChina
| | - Yi Gong
- College of Marine SciencesShanghai Ocean UniversityShanghaiChina
- Laboratory for Marine Fisheries Science and Food Production ProcessesQingdao National Laboratory for Marine Science and TechnologyQingdaoChina
- The Key Laboratory of Sustainable Exploitation of Oceanic Fisheries ResourcesMinistry of EducationShanghaiChina
- National Engineering Research Centre for Oceanic FisheriesShanghai Ocean UniversityShanghaiChina
| | - Feng Wu
- College of Marine SciencesShanghai Ocean UniversityShanghaiChina
- Laboratory for Marine Fisheries Science and Food Production ProcessesQingdao National Laboratory for Marine Science and TechnologyQingdaoChina
- The Key Laboratory of Sustainable Exploitation of Oceanic Fisheries ResourcesMinistry of EducationShanghaiChina
- National Engineering Research Centre for Oceanic FisheriesShanghai Ocean UniversityShanghaiChina
| | - Yunkai Li
- College of Marine SciencesShanghai Ocean UniversityShanghaiChina
- Laboratory for Marine Fisheries Science and Food Production ProcessesQingdao National Laboratory for Marine Science and TechnologyQingdaoChina
- The Key Laboratory of Sustainable Exploitation of Oceanic Fisheries ResourcesMinistry of EducationShanghaiChina
- National Engineering Research Centre for Oceanic FisheriesShanghai Ocean UniversityShanghaiChina
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Besnard L, Le Croizier G, Galván-Magaña F, Point D, Kraffe E, Ketchum J, Martinez Rincon RO, Schaal G. Foraging depth depicts resource partitioning and contamination level in a pelagic shark assemblage: Insights from mercury stable isotopes. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2021; 283:117066. [PMID: 33892372 DOI: 10.1016/j.envpol.2021.117066] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 03/29/2021] [Accepted: 03/30/2021] [Indexed: 06/12/2023]
Abstract
The decline of shark populations in the world ocean is affecting ecosystem structure and function in an unpredictable way and new ecological information is today needed to better understand the role of sharks in their habitats. In particular, the characterization of foraging patterns is crucial to understand and foresee the evolution of dynamics between sharks and their prey. Many shark species use the mesopelagic area as a major foraging ground but the degree to which different pelagic sharks rely on this habitat remains overlooked. In order to depict the vertical dimension of their trophic ecology, we used mercury stable isotopes in the muscle of three pelagic shark species (the blue shark Prionace glauca, the shortfin mako shark Isurus oxyrinchus and the smooth hammerhead shark Sphyrna zygaena) from the northeastern Pacific region. The Δ199Hg values, ranging from 1.40 to 2.13‰ in sharks, suggested a diet mostly based on mesopelagic prey in oceanic habitats. We additionally used carbon and nitrogen stable isotopes (δ13C, δ15N) alone or in combination with Δ199Hg values, to assess resource partitioning between the three shark species. Adding Δ199Hg resulted in a decrease in trophic overlap estimates compared to those based on δ13C/δ15N alone, demonstrating that multi-isotope modeling is needed for accurate trophic description of the three species. Mainly, it reveals that they forage at different average depths and that resource partitioning is mostly expressed through the vertical dimension within pelagic shark assemblages. Concomitantly, muscle total mercury concentration (THg) differed between species and increased with feeding depth. Overall, this study highlights the key role of the mesopelagic zone for shark species foraging among important depth gradients and reports new ecological information on trophic competition using mercury isotopes. It also suggests that foraging depth may play a pivotal role in the differences between muscle THg from co-occurring high trophic level shark species.
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Affiliation(s)
- Lucien Besnard
- Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzane, France.
| | - Gaël Le Croizier
- UMR Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), 14 Avenue Edouard Belin, 31400, Toulouse, France
| | - Felipe Galván-Magaña
- Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, Av. IPN S/n, 23096, La Paz, B.C.S., Mexico
| | - David Point
- UMR Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), 14 Avenue Edouard Belin, 31400, Toulouse, France
| | - Edouard Kraffe
- Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzane, France
| | - James Ketchum
- Pelagios-Kakunja, Cuauhtémoc 155, 23096, La Paz, B.C.S., Mexico
| | - Raul Octavio Martinez Rincon
- CONACyT-Centro de Investigaciónes Biológicas Del Noroeste, S.C. (CIBNOR), Av. IPN 195, 23096, La Paz, B.C.S., Mexico
| | - Gauthier Schaal
- Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzane, France
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Williamson MJ, Tebbs EJ, Dawson TP, Curnick DJ, Ferretti F, Carlisle AB, Chapple TK, Schallert RJ, Tickler DM, Harrison XA, Block BA, Jacoby DM. Analysing detection gaps in acoustic telemetry data to infer differential movement patterns in fish. Ecol Evol 2021; 11:2717-2730. [PMID: 33767831 PMCID: PMC7981221 DOI: 10.1002/ece3.7226] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 12/15/2020] [Accepted: 01/07/2021] [Indexed: 12/02/2022] Open
Abstract
A wide array of technologies are available for gaining insight into the movement of wild aquatic animals. Although acoustic telemetry can lack the fine-scale spatial resolution of some satellite tracking technologies, the substantially longer battery life can yield important long-term data on individual behavior and movement for low per-unit cost. Typically, however, receiver arrays are designed to maximize spatial coverage at the cost of positional accuracy leading to potentially longer detection gaps as individuals move out of range between monitored locations. This is particularly true when these technologies are deployed to monitor species in hard-to-access locations.Here, we develop a novel approach to analyzing acoustic telemetry data, using the timing and duration of gaps between animal detections to infer different behaviors. Using the durations between detections at the same and different receiver locations (i.e., detection gaps), we classify behaviors into "restricted" or potential wider "out-of-range" movements synonymous with longer distance dispersal. We apply this method to investigate spatial and temporal segregation of inferred movement patterns in two sympatric species of reef shark within a large, remote, marine protected area (MPA). Response variables were generated using network analysis, and drivers of these movements were identified using generalized linear mixed models and multimodel inference.Species, diel period, and season were significant predictors of "out-of-range" movements. Silvertip sharks were overall more likely to undertake "out-of-range" movements, compared with gray reef sharks, indicating spatial segregation, and corroborating previous stable isotope work between these two species. High individual variability in "out-of-range" movements in both species was also identified.We present a novel gap analysis of telemetry data to help infer differential movement and space use patterns where acoustic coverage is imperfect and other tracking methods are impractical at scale. In remote locations, inference may be the best available tool and this approach shows that acoustic telemetry gap analysis can be used for comparative studies in fish ecology, or combined with other research techniques to better understand functional mechanisms driving behavior.
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Affiliation(s)
- Michael J. Williamson
- Department of GeographyKing’s College LondonLondonUK
- Institute of ZoologyZoological Society of LondonLondonUK
| | - Emma J. Tebbs
- Department of GeographyKing’s College LondonLondonUK
| | | | | | - Francesco Ferretti
- Department of Fish and Wildlife ConservationVirginia TechBlacksburgVaUSA
| | - Aaron B. Carlisle
- Hopkins Marine StationStanford UniversityPacific GroveCAUSA
- School of Marine Science and PolicyUniversity of DelawareLewesDEUSA
| | | | | | - David M. Tickler
- Marine Futures LabSchool of Biological SciencesUniversity of Western AustraliaPerthWAAustralia
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Le Croizier G, Lorrain A, Schaal G, Ketchum J, Hoyos-Padilla M, Besnard L, Munaron JM, Le Loc'h F, Point D. Trophic resources and mercury exposure of two silvertip shark populations in the Northeast Pacific Ocean. CHEMOSPHERE 2020; 253:126645. [PMID: 32283423 DOI: 10.1016/j.chemosphere.2020.126645] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Revised: 03/21/2020] [Accepted: 03/27/2020] [Indexed: 06/11/2023]
Abstract
Worldwide shark populations have experienced rapid declines over the last decades, mainly due to overfishing. Marine protected areas (MPAs) have thus become an indispensable tool for the protection of these marine predators. Two recently-created MPAs in the Northeast Pacific Ocean, the Revillagigedo National Park and Clipperton Atoll, are characterized by different trophic structures potentially influencing the trophic niche and contaminant exposure of resident sharks in these two sites. In this context, we used carbon (δ13C) and nitrogen (δ15N) stable isotope analyzes as well as total mercury concentrations ([THg]) to assess the effect of foraging site on the trophic niche and Hg levels of juvenile silvertip (ST) sharks Carcharhinus albimarginatus. Analyzing fin clip samples from Revillagigedo and Clipperton, we found that shark δ15N varied spatially in relation to δ15N baselines, suggesting similar trophic position in both MPAs. Moreover, δ13C values indicated that ST sharks from Revillagigedo would feed on different food webs (i.e. both benthic and pelagic) while individuals from Clipperton would only rely on benthic food webs. These differences between MPAs led to a weak overlap of isotopic niches between the two populations, highlighting the site residency of juvenile ST sharks. Within each population, [THg] was not correlated with trophic tracers (δ15N and δ13C) and was also similar between populations. This study revealed no influence of site or food web in [THg] and raises the question of the origin of Hg exposure for reef shark populations in the Northeast Pacific Ocean.
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Affiliation(s)
- Gaël Le Croizier
- Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), UMR 5563 CNRS/IRD/Université Paul Sabatier, 14 Avenue Edouard Belin, 31400, Toulouse, France; Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280, Plouzané, France.
| | - Anne Lorrain
- Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280, Plouzané, France
| | - Gauthier Schaal
- Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280, Plouzané, France
| | - James Ketchum
- Pelagios Kakunjá A.C., Sinaloa 1540, Las Garzas, 23070, La Paz, Baja California Sur, Mexico; Centro de Investigaciones Biológicas del Noroeste (CIBNOR), La Paz, Baja California Sur, 23096, Mexico
| | - Mauricio Hoyos-Padilla
- Pelagios Kakunjá A.C., Sinaloa 1540, Las Garzas, 23070, La Paz, Baja California Sur, Mexico; Centro de Investigaciones Biológicas del Noroeste (CIBNOR), La Paz, Baja California Sur, 23096, Mexico; Fins Attached Marine Conservation, Colorado Springs, USA
| | - Lucien Besnard
- Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280, Plouzané, France
| | | | | | - David Point
- Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), UMR 5563 CNRS/IRD/Université Paul Sabatier, 14 Avenue Edouard Belin, 31400, Toulouse, France
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Jacoby DMP, Ferretti F, Freeman R, Carlisle AB, Chapple TK, Curnick DJ, Dale JJ, Schallert RJ, Tickler D, Block BA. Shark movement strategies influence poaching risk and can guide enforcement decisions in a large, remote marine protected area. J Appl Ecol 2020. [DOI: 10.1111/1365-2664.13654] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
| | - Francesco Ferretti
- Department of Fish and Wildlife Conservation Virginia Tech Blacksburg VA USA
- Hopkins Marine Station Stanford University Pacific Grove CA USA
| | - Robin Freeman
- Institute of Zoology Zoological Society of London London UK
| | - Aaron B. Carlisle
- Hopkins Marine Station Stanford University Pacific Grove CA USA
- School of Marine Science and Policy University of Delaware Lewes DE USA
| | - Taylor K. Chapple
- Hopkins Marine Station Stanford University Pacific Grove CA USA
- Coastal Oregon Marine Experiment Station Department of Fisheries and Wildlife Hatfield Marine Science Center Oregon State University Newport OR USA
| | | | | | | | - David Tickler
- Hopkins Marine Station Stanford University Pacific Grove CA USA
- The UWA Oceans InstituteUniversity of Western Australia Crawley WA Australia
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Seubert EA, Hussey N, Powers SP, Valentine JF, Drymon JM. Assessing trophic flexibility of a predator assemblage across a large estuarine seascape using blood plasma stable isotope analysis. FOOD WEBS 2019. [DOI: 10.1016/j.fooweb.2019.e00132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Raoult V, Broadhurst MK, Peddemors VM, Williamson JE, Gaston TF. Resource use of great hammerhead sharks (Sphyrna mokarran) off eastern Australia. JOURNAL OF FISH BIOLOGY 2019; 95:1430-1440. [PMID: 31613987 DOI: 10.1111/jfb.14160] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 09/27/2019] [Indexed: 06/10/2023]
Abstract
Great hammerhead sharks Sphyrna mokarran are the largest member of Sphyrnidae, yet the roles of these large sharks in the food webs of coastal ecosystems are still poorly understood. Here we obtained samples of muscle, liver and vertebrae from large S. mokarran (234-383 cm total length; LT ) caught as by-catch off eastern Australia and used stable-isotope analyses of δ15 N, δ13 C and δ34 S to infer their resource use and any associated ontogenetic patterns. The results indicated large S. mokarran are apex predators primarily relying on other sharks and rays for their diet, with a preference for benthic resources such as Australian cownose rays Rhinoperon neglecta during the austral summer. Teleosts, cephalopods and crustaceans were not significant components of S. mokarran diets, though some conspecifics appeared to rely on more diverse resources over the austral summer. Ontogenetic shifts in resource use were detected but trajectories of the increases in trophic level varied among individuals. Most S. mokarran had non-linear trajectories in ontogenetic resource-use shifts implying size was not the main explanatory factor. Stable isotope values of δ13 C and δ34 S in muscle suggest S. mokarran span coastal, pelagic and benthic food webs in eastern Australia.
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Affiliation(s)
- Vincent Raoult
- School of Environmlental and Life Sciences, University of Newcastle, Ourimbah, Australia
| | - Matt K Broadhurst
- New South Wales Department of Industries, Fisheries Conservation Technology Unit, National Marine Science Centre, Coffs Harbour, Australia
| | - Vic M Peddemors
- New South Wales of Department of Primary Industries, Fisheries, Sydney Institute of Marine Science, Mosman, Australia
| | - Jane E Williamson
- Department of Biological Sciences, Macquarie University, Sydney, Australia
| | - Troy F Gaston
- School of Environmlental and Life Sciences, University of Newcastle, Ourimbah, Australia
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