Migratory movements in response to seasonal resources often influence population structure and dy... more Migratory movements in response to seasonal resources often influence population structure and dynamics. Yet in mobile marine predators, population genetic consequences of such repetitious behaviour remain inaccessible without comprehensive sampling strategies. Temporal genetic sampling of seasonally recurring aggregations of planktivorous basking sharks, Cetorhinus maximus, in the Northeast Atlantic (NEA) affords an opportunity to resolve individual re-encounters at key sites with population connectivity and patterns of relatedness. Genetic tagging (19 microsatellites) revealed 18% of re-sampled individuals in the NEA demonstrated inter/multi-annual site-specific re-encounters. High genetic connectivity and migration between aggregation sites indicate the Irish Sea as an important movement corridor, with a contemporary effective population estimate (Ne) of 382 (CI = 241–830). We contrast the prevailing view of high gene flow across oceanic regions with evidence of population struct...
Ecological and community differences have been noted across coral reef ecosystems with varying le... more Ecological and community differences have been noted across coral reef ecosystems with varying levels of anthropogenic intrusion, with striking declines of apex predator densities documented where human presence has historically been the highest. Within western Atlantic waters, one of the most common predators inhabiting coral reef ecosystems is the Caribbean reef shark (Carcharhinus perezi). Given the vulnerability of this species to fisheries and its potentially important ecological role as an apex predator, we assessed the overall genetic diversity and connectivity across its tropical western Atlantic distribution using both nuclear and mitochondrial DNA. Caribbean reef sharks demonstrated extremely low levels of genetic diversity across all surveyed loci relative to all other shark species analyzed to date, which may be due to a recent evolutionary origin. Nevertheless, nuclear microsatellite loci revealed population structure between Brazilian sites and populations from The Bahamas and Caribbean Sea (FST \u3e 0.0182; P 0.05). In contrast, concatenated mitochondrial and mitochondrial/nuclear sequences revealed low but significant genetic differentiation across most of the surveyed locations. These patterns may reflect either historical patterns of dispersal or contrasting patterns of movement between male and female sharks. Although tagging and tracking data suggest these animals typically exhibit strong site attachment, our study reveals complex population structure with evidence supporting contemporary long distance mixing, at least by males, which should be incorporated into management plans for this species
AbstractInvasive lionfish (Pterois volitans/miles complex) now permeate the entire tropical weste... more AbstractInvasive lionfish (Pterois volitans/miles complex) now permeate the entire tropical western Atlantic, Caribbean Sea, and Gulf of Mexico, but lionfish abundance has been measured only in select locations in the field. Despite its rapid range expansion, a comprehensive meta-population analysis of lionfish ‘sources’ and ‘sinks’ and consequentially the invader’s potential abundance and impacts on economically important, sympatric reef fishes have not been assessed. These data are urgently needed to spatially direct control efforts and to plan for and perhaps mitigate lionfish-caused damage. Here, we use a biophysical computer model to: (1) forecast larval lionfish sources and sinks that are also delineated as low to high lionfish ‘density zones’ throughout their invaded range, and (2) assess the potential vulnerability of five grouper and snapper species—Epinephelus morio, Mycteroperca microlepis, Epinephelus flavolimbatus, Lutjanus campechanus, and Rhomboplites aurorubens—to lionfish within these density zones in the Gulf of Mexico. Our results suggest that the west Florida shelf and nearshore waters of Texas, USA, and Guyana, South America, function both as lionfish sources and sinks and should be a high priority for targeted lionfish control. Furthermore, of the five groupers and snappers studied, the high fishery value E. morio (red grouper) is the Gulf of Mexico species most at risk from lionfish. Lacking a comprehensive lionfish control policy, these risk exposure data inform managers where removals should be focused and demonstrate the risk to five sympatric native groupers and snappers in the Gulf of Mexico that may be susceptible to dense lionfish aggregations, should control efforts fail.
Recent artisanal elasmobranch fishery surveys in the Gulf of California and Pacific coast of Mexi... more Recent artisanal elasmobranch fishery surveys in the Gulf of California and Pacific coast of Mexico have indicated that batoids are a much moreimportant component of landings than previously estimated. Two butterflyrays, Gymnura crebripunctata and G. marmorata, are recognized in the Mexican Pacific and are among the primary elasmobranchs observed in these landings. The validity of these species was first questioned in 1928, but evidence supporting synonymy has been inconclusive. However, the primary characteristics used to distinguish the species (inter-orbital width and pre-orbital length) are known to be sexually dimorphic features in Gymnura micrura. To determine if G. crebripunctata and G. marmorataare valid species or male and female morphs of the same species, multiple analytical techniques have been applied. Heart and white muscle tissues were collected from fishery-derived specimens in the states of Sonora and Baja California Sur, Mexico. Similarity of the two species was examined through direct sequence comparison and phylogenetic analyses of approximately 445 base pairs of the mitochondrial cytochorme b locus, including other congeners as outgroups. Measurements, vertebral and spiral valve counts were obtained from and and compared to field and museum specimens. We report here on the preliminary results from these analyses
The globally distributed, coastal-pelagic scalloped hammerhead shark (Sphyrna lewini) is widely e... more The globally distributed, coastal-pelagic scalloped hammerhead shark (Sphyrna lewini) is widely exploited for its fins and meat. Drastic population declines have resulted in its categorization as Endangered on the IUCN Red-List and inclusion under the US Endangered Species Act. This species is famously recognized for its tendency to form seasonal aggregations of mostly adult females around seamounts and offshore islands in the Eastern Tropical Pacific (ETP), including the northern Galápagos Islands. Female scalloped hammerheads in the ETP are also known to utilize shallow mangrove bays along the Central and South American mainland for parturition. My study objectives are to determine: 1) if parent-offspring relationships exist between the adult sharks in the Galápagos and young-of-year (YOY) sharks sampled in coastal nursery areas of Panama, Ecuador, Costa Rica, Colombia and the Galápagos Islands, 2) genetic relatedness of YOY animals sampled in individual coastal nursery areas, and 3) population structure of YOY sharks to test for hypothesized female philopatry to coastal parturition areas. Results to date using five biparentally inherited nuclear microsatellite and maternally-inherited mitochondrial DNA sequence markers show little genetic population structure among mainland sampled sites in the ETP; however, significant pairwise genetic differences were found in the mitochondrial DNA between the Galápagos YOY and all mainland YOY samples. No parent-offspring relationships were found between the adult Galápagos aggregation (n=130 females) and YOY individuals (n=320) in the ETP. Analysis of the five biparentally-inherited markers found 33 full-sibling pairs and 1208 half-sibling pairs among the 5 nurseries sampled. The high percentage of half-siblings suggests a polyandrous mating system in scalloped hammerheads in the ETP, consistent with similar findings for this species in the Indian Ocean. Analysis with additional microsatellite markers is ongoing to examine the comparative genetic diversity of the iconic Galápagos aggregation animals to scalloped hammerheads from other regions
Foraging behavior and interaction with prey is an integral component of the ecological niche of p... more Foraging behavior and interaction with prey is an integral component of the ecological niche of predators but is inherently difficult to observe for highly mobile animals in the marine environment. Billfishes have been described as energy speculators, expending a large amount of energy foraging, expecting to offset high costs with periodic high energetic gain. Surface-based group feeding of sailfish,Istiophorus platypterus,is commonly observed, yet sailfish are believed to be largely solitary roaming predators with high metabolic requirements, suggesting that individual foraging also represents a major component of predator–prey interactions. Here, we use biologging data and video to examine daily activity levels and foraging behavior, estimate metabolic costs, and document a solitary predation event for a 40 kg sailfish. We estimate a median active metabolic rate of 218.9 ± 70.5 mgO2kg−1 h−1which increased to 518.8 ± 586.3 mgO2kg−1 h−1during prey pursuit. Assuming a successful pred...
Cosmopolitan marine pelagic species display variable patterns of population connectivity among th... more Cosmopolitan marine pelagic species display variable patterns of population connectivity among the world’s major oceans. While this information is crucial for informing management, information is lacking for many ecologically important species, including apex predators. In this study we examine patterns of genetic structure in the broadnose sevengill shark, Notorynchus cepedianus across its global distribution. We estimate patterns of connectivity among broadnose sevengill shark populations from three major oceanic regions (South Atlantic, Oceania and Eastern Pacific) by contrasting mitochondrial and nuclear DNA haplotype frequencies. We also produced time calibrated Bayesian Inference phylogenetic reconstructions to analyses global phylogeographic patterns and estimate divergence times among distinctive shark lineages. Our results demonstrate significant genetic differentiation among oceanic regions ( Φ ST = 0.9789, P < 0.0001) and a lack of genetic structuring within regions ( Φ ST = − 0.007; P = 0.479). Time calibrated Bayesian Inference phylogenetic reconstructions indicate that the observed patterns of genetic structure among oceanic regions are historical, with regional populations estimated to have diverged from a common ancestor during the early to mid-Pleistocene. Our results indicate significant genetic structuring and a lack of gene flow among broadnose sevengill shark populations from the South Atlantic, Oceania and Eastern Pacific regions. Evidence of deep lineage divergences coinciding with the early to mid-Pleistocene suggests historical glacial cycling has contributed to the vicariant divergence of broadnose sevengill shark populations from different ocean basins. These finding will help inform global management of broadnose sevengill shark populations, and provides new insights into historical and contemporary evolutionary processes shaping populations of this ecologically important apex predator .
Transboundary marine species have an increased risk of overexploitation as management regimes and... more Transboundary marine species have an increased risk of overexploitation as management regimes and enforcement can vary among states. The complex geopolitical layout of exclusive economic zones (EEZs) in the Western Indian Ocean (WIO) introduces the potential for migratory species to cross multiple boundaries, consequently a lack of scientific data could complicate regional management. In the current study, we highlight both the relative lack of spatial data available in the WIO, and the prevalence of transboundary movements in species that have previously been studied in the region. Five tiger sharks Galeocerdo cuvier were tracked with near real‐time positioning (SPOT) satellite tags to determine individual shark movements relative to EEZs within the WIO. Concurrently, a literature search was performed to identify all satellite telemetry studies conducted to date in the WIO for marine megafaunal species, and the results compared to global satellite telemetry effort. Finally, the sat...
Aquatic Conservation: Marine and Freshwater Ecosystems, 2018
The night shark, Carcharhinus signatus, is a mesopelagic, semi‐oceanic shark species found only i... more The night shark, Carcharhinus signatus, is a mesopelagic, semi‐oceanic shark species found only in the Atlantic Ocean. It is one of the most frequently caught sharks in pelagic longline fisheries and is classified as Vulnerable by the International Union for the Conservation of Nature (IUCN). Despite their prevalence in commercial fisheries, the population genetic structure of the night shark has not been assessed. The present study investigated the genetic diversity, genetic connectivity, and phylogeography of the species throughout the western Atlantic Ocean, based on complete mitochondrial control region (mtCR) sequence data (n = 152) and genotypic data from nine nuclear microsatellites (n = 119). The mtCR sequence revealed 19 haplotypes, with overall haplotype and nucleotide diversities of 0.74 (±0.027) and 0.0034 (±0.0019), respectively, whereas the nuclear microsatellite observed and expected heterozygosities were 0.408 and 0.421, respectively. There was significant population...
The Nassau grouper (Epinephelus striatus) has sustained large declines across its distribution, i... more The Nassau grouper (Epinephelus striatus) has sustained large declines across its distribution, including extirpation of many of its fish spawning aggregations (FSAs). Within US Virgin Islands (USVI) waters, Nassau grouper FSAs were overfished until their disappearance in the 1970s and 1980s. In the early 2000s, however, Nassau grouper were found gathering at Grammanik Bank, USVI, a mesophotic coral reef adjacent to one of the extinct aggregation sites, and regulatory protective measures were implemented to protect this fledgling FSA. The population genetic dynamics of this rapid FSA deterioration followed by protection-facilitated, incipient recovery are unknown. We addressed two objectives: (1) we explored which factors (i.e., local vs. external recruitment) might be key in shaping the USVI FSA recovery; and (2) we examined the consequences of severe past overfishing on this FSA’s current genetic status. We genotyped individuals (15 microsatellites) from the USVI FSA comprising three successive spawning years (2008–2010), as well as individuals from a much larger, presumably less impacted, Nassau grouper FSA in the Cayman Islands, to assess their comparative population dynamics. No population structure was detected between the USVI and Cayman FSAs (FST = −0.0004); however, a temporally waning, genetic bottleneck signal was detected in the USVI FSA. Parentage analysis failed to identify any parent–offspring matches between USVI FSA adults and nearby juveniles, and relatedness analysis showed low levels of genetic relatedness among USVI FSA individuals. Genetic diversity across USVI FSA temporal collections was relatively high, and no marked differences were found between the USVI and Cayman FSAs. These collective results suggest that external recruitment is an important driver of the USVI FSA recovery. Furthermore, despite an apparent genetic bottleneck, the genetic diversity of USVI Nassau grouper has not been severely compromised. Our findings also provide a baseline for future genetic monitoring of the nascent USVI aggregation.
Knowledge of genetic connectivity dynamics in the world's large-bodied, highly migratory, ape... more Knowledge of genetic connectivity dynamics in the world's large-bodied, highly migratory, apex predator sharks across their global ranges is limited. One such species, the tiger shark (Galeocerdo cuvier), occurs worldwide in warm temperate and tropical waters, uses remarkably diverse habitats (nearshore to pelagic) and possesses a generalist diet that can structure marine ecosystems through top-down processes. We investigated the phylogeography and the global population structure of this exploited, phylogenetically enigmatic shark by using 10 nuclear microsatellites (n = 380) and sequences from the mitochondrial control region (CR, n = 340) and cytochrome oxidase I gene (n = 100). All three marker classes showed the genetic differentiation between tiger sharks from the western Atlantic and Indo-Pacific ocean basins (microsatellite FST > 0.129; CR ΦST > 0.497), the presence of North vs. southwestern Atlantic differentiation and the isolation of tiger sharks sampled from H...
Overfishing is a primary cause of population declines for many shark species of conservation conc... more Overfishing is a primary cause of population declines for many shark species of conservation concern. However, means of obtaining information on fishery interactions and mortality, necessary for the development of successful conservation strategies, are often fishery-dependent and of questionable quality for many species of commercially exploited pelagic sharks. We used satellite telemetry as a fisheries-independent tool to document fisheries interactions, and quantify fishing mortality of the highly migratory shortfin mako shark (<i>Isurus oxyrinchus</i>) in the western North Atlantic Ocean. Forty satellite-tagged shortfin mako sharks tracked over 3 years entered the Exclusive Economic Zones of 19 countries and were harvested in fisheries of five countries, with 30% of tagged sharks harvested. Our tagging-derived estimates of instantaneous fishing mortality rates (<i>F</i> = 0.19–0.56) were 10-fold higher than previous estimates from fisheries-dependent data (approx. 0.015–0.024), suggesting data used in stock assessments may considerably underestimate fishing mortality. Additionally, our estimates of <i>F</i> were greater than those associated with maximum sustainable yield, suggesting a state of overfishing. This information has direct application to evaluations of stock status and for effective management of populations, and thus satellite tagging studies have potential to provide more accurate estimates of fishing mortality and survival than traditional fishery-dependent methodology.
Migratory movements in response to seasonal resources often influence population structure and dy... more Migratory movements in response to seasonal resources often influence population structure and dynamics. Yet in mobile marine predators, population genetic consequences of such repetitious behaviour remain inaccessible without comprehensive sampling strategies. Temporal genetic sampling of seasonally recurring aggregations of planktivorous basking sharks, Cetorhinus maximus, in the Northeast Atlantic (NEA) affords an opportunity to resolve individual re-encounters at key sites with population connectivity and patterns of relatedness. Genetic tagging (19 microsatellites) revealed 18% of re-sampled individuals in the NEA demonstrated inter/multi-annual site-specific re-encounters. High genetic connectivity and migration between aggregation sites indicate the Irish Sea as an important movement corridor, with a contemporary effective population estimate (Ne) of 382 (CI = 241–830). We contrast the prevailing view of high gene flow across oceanic regions with evidence of population struct...
Ecological and community differences have been noted across coral reef ecosystems with varying le... more Ecological and community differences have been noted across coral reef ecosystems with varying levels of anthropogenic intrusion, with striking declines of apex predator densities documented where human presence has historically been the highest. Within western Atlantic waters, one of the most common predators inhabiting coral reef ecosystems is the Caribbean reef shark (Carcharhinus perezi). Given the vulnerability of this species to fisheries and its potentially important ecological role as an apex predator, we assessed the overall genetic diversity and connectivity across its tropical western Atlantic distribution using both nuclear and mitochondrial DNA. Caribbean reef sharks demonstrated extremely low levels of genetic diversity across all surveyed loci relative to all other shark species analyzed to date, which may be due to a recent evolutionary origin. Nevertheless, nuclear microsatellite loci revealed population structure between Brazilian sites and populations from The Bahamas and Caribbean Sea (FST \u3e 0.0182; P 0.05). In contrast, concatenated mitochondrial and mitochondrial/nuclear sequences revealed low but significant genetic differentiation across most of the surveyed locations. These patterns may reflect either historical patterns of dispersal or contrasting patterns of movement between male and female sharks. Although tagging and tracking data suggest these animals typically exhibit strong site attachment, our study reveals complex population structure with evidence supporting contemporary long distance mixing, at least by males, which should be incorporated into management plans for this species
AbstractInvasive lionfish (Pterois volitans/miles complex) now permeate the entire tropical weste... more AbstractInvasive lionfish (Pterois volitans/miles complex) now permeate the entire tropical western Atlantic, Caribbean Sea, and Gulf of Mexico, but lionfish abundance has been measured only in select locations in the field. Despite its rapid range expansion, a comprehensive meta-population analysis of lionfish ‘sources’ and ‘sinks’ and consequentially the invader’s potential abundance and impacts on economically important, sympatric reef fishes have not been assessed. These data are urgently needed to spatially direct control efforts and to plan for and perhaps mitigate lionfish-caused damage. Here, we use a biophysical computer model to: (1) forecast larval lionfish sources and sinks that are also delineated as low to high lionfish ‘density zones’ throughout their invaded range, and (2) assess the potential vulnerability of five grouper and snapper species—Epinephelus morio, Mycteroperca microlepis, Epinephelus flavolimbatus, Lutjanus campechanus, and Rhomboplites aurorubens—to lionfish within these density zones in the Gulf of Mexico. Our results suggest that the west Florida shelf and nearshore waters of Texas, USA, and Guyana, South America, function both as lionfish sources and sinks and should be a high priority for targeted lionfish control. Furthermore, of the five groupers and snappers studied, the high fishery value E. morio (red grouper) is the Gulf of Mexico species most at risk from lionfish. Lacking a comprehensive lionfish control policy, these risk exposure data inform managers where removals should be focused and demonstrate the risk to five sympatric native groupers and snappers in the Gulf of Mexico that may be susceptible to dense lionfish aggregations, should control efforts fail.
Recent artisanal elasmobranch fishery surveys in the Gulf of California and Pacific coast of Mexi... more Recent artisanal elasmobranch fishery surveys in the Gulf of California and Pacific coast of Mexico have indicated that batoids are a much moreimportant component of landings than previously estimated. Two butterflyrays, Gymnura crebripunctata and G. marmorata, are recognized in the Mexican Pacific and are among the primary elasmobranchs observed in these landings. The validity of these species was first questioned in 1928, but evidence supporting synonymy has been inconclusive. However, the primary characteristics used to distinguish the species (inter-orbital width and pre-orbital length) are known to be sexually dimorphic features in Gymnura micrura. To determine if G. crebripunctata and G. marmorataare valid species or male and female morphs of the same species, multiple analytical techniques have been applied. Heart and white muscle tissues were collected from fishery-derived specimens in the states of Sonora and Baja California Sur, Mexico. Similarity of the two species was examined through direct sequence comparison and phylogenetic analyses of approximately 445 base pairs of the mitochondrial cytochorme b locus, including other congeners as outgroups. Measurements, vertebral and spiral valve counts were obtained from and and compared to field and museum specimens. We report here on the preliminary results from these analyses
The globally distributed, coastal-pelagic scalloped hammerhead shark (Sphyrna lewini) is widely e... more The globally distributed, coastal-pelagic scalloped hammerhead shark (Sphyrna lewini) is widely exploited for its fins and meat. Drastic population declines have resulted in its categorization as Endangered on the IUCN Red-List and inclusion under the US Endangered Species Act. This species is famously recognized for its tendency to form seasonal aggregations of mostly adult females around seamounts and offshore islands in the Eastern Tropical Pacific (ETP), including the northern Galápagos Islands. Female scalloped hammerheads in the ETP are also known to utilize shallow mangrove bays along the Central and South American mainland for parturition. My study objectives are to determine: 1) if parent-offspring relationships exist between the adult sharks in the Galápagos and young-of-year (YOY) sharks sampled in coastal nursery areas of Panama, Ecuador, Costa Rica, Colombia and the Galápagos Islands, 2) genetic relatedness of YOY animals sampled in individual coastal nursery areas, and 3) population structure of YOY sharks to test for hypothesized female philopatry to coastal parturition areas. Results to date using five biparentally inherited nuclear microsatellite and maternally-inherited mitochondrial DNA sequence markers show little genetic population structure among mainland sampled sites in the ETP; however, significant pairwise genetic differences were found in the mitochondrial DNA between the Galápagos YOY and all mainland YOY samples. No parent-offspring relationships were found between the adult Galápagos aggregation (n=130 females) and YOY individuals (n=320) in the ETP. Analysis of the five biparentally-inherited markers found 33 full-sibling pairs and 1208 half-sibling pairs among the 5 nurseries sampled. The high percentage of half-siblings suggests a polyandrous mating system in scalloped hammerheads in the ETP, consistent with similar findings for this species in the Indian Ocean. Analysis with additional microsatellite markers is ongoing to examine the comparative genetic diversity of the iconic Galápagos aggregation animals to scalloped hammerheads from other regions
Foraging behavior and interaction with prey is an integral component of the ecological niche of p... more Foraging behavior and interaction with prey is an integral component of the ecological niche of predators but is inherently difficult to observe for highly mobile animals in the marine environment. Billfishes have been described as energy speculators, expending a large amount of energy foraging, expecting to offset high costs with periodic high energetic gain. Surface-based group feeding of sailfish,Istiophorus platypterus,is commonly observed, yet sailfish are believed to be largely solitary roaming predators with high metabolic requirements, suggesting that individual foraging also represents a major component of predator–prey interactions. Here, we use biologging data and video to examine daily activity levels and foraging behavior, estimate metabolic costs, and document a solitary predation event for a 40 kg sailfish. We estimate a median active metabolic rate of 218.9 ± 70.5 mgO2kg−1 h−1which increased to 518.8 ± 586.3 mgO2kg−1 h−1during prey pursuit. Assuming a successful pred...
Cosmopolitan marine pelagic species display variable patterns of population connectivity among th... more Cosmopolitan marine pelagic species display variable patterns of population connectivity among the world’s major oceans. While this information is crucial for informing management, information is lacking for many ecologically important species, including apex predators. In this study we examine patterns of genetic structure in the broadnose sevengill shark, Notorynchus cepedianus across its global distribution. We estimate patterns of connectivity among broadnose sevengill shark populations from three major oceanic regions (South Atlantic, Oceania and Eastern Pacific) by contrasting mitochondrial and nuclear DNA haplotype frequencies. We also produced time calibrated Bayesian Inference phylogenetic reconstructions to analyses global phylogeographic patterns and estimate divergence times among distinctive shark lineages. Our results demonstrate significant genetic differentiation among oceanic regions ( Φ ST = 0.9789, P < 0.0001) and a lack of genetic structuring within regions ( Φ ST = − 0.007; P = 0.479). Time calibrated Bayesian Inference phylogenetic reconstructions indicate that the observed patterns of genetic structure among oceanic regions are historical, with regional populations estimated to have diverged from a common ancestor during the early to mid-Pleistocene. Our results indicate significant genetic structuring and a lack of gene flow among broadnose sevengill shark populations from the South Atlantic, Oceania and Eastern Pacific regions. Evidence of deep lineage divergences coinciding with the early to mid-Pleistocene suggests historical glacial cycling has contributed to the vicariant divergence of broadnose sevengill shark populations from different ocean basins. These finding will help inform global management of broadnose sevengill shark populations, and provides new insights into historical and contemporary evolutionary processes shaping populations of this ecologically important apex predator .
Transboundary marine species have an increased risk of overexploitation as management regimes and... more Transboundary marine species have an increased risk of overexploitation as management regimes and enforcement can vary among states. The complex geopolitical layout of exclusive economic zones (EEZs) in the Western Indian Ocean (WIO) introduces the potential for migratory species to cross multiple boundaries, consequently a lack of scientific data could complicate regional management. In the current study, we highlight both the relative lack of spatial data available in the WIO, and the prevalence of transboundary movements in species that have previously been studied in the region. Five tiger sharks Galeocerdo cuvier were tracked with near real‐time positioning (SPOT) satellite tags to determine individual shark movements relative to EEZs within the WIO. Concurrently, a literature search was performed to identify all satellite telemetry studies conducted to date in the WIO for marine megafaunal species, and the results compared to global satellite telemetry effort. Finally, the sat...
Aquatic Conservation: Marine and Freshwater Ecosystems, 2018
The night shark, Carcharhinus signatus, is a mesopelagic, semi‐oceanic shark species found only i... more The night shark, Carcharhinus signatus, is a mesopelagic, semi‐oceanic shark species found only in the Atlantic Ocean. It is one of the most frequently caught sharks in pelagic longline fisheries and is classified as Vulnerable by the International Union for the Conservation of Nature (IUCN). Despite their prevalence in commercial fisheries, the population genetic structure of the night shark has not been assessed. The present study investigated the genetic diversity, genetic connectivity, and phylogeography of the species throughout the western Atlantic Ocean, based on complete mitochondrial control region (mtCR) sequence data (n = 152) and genotypic data from nine nuclear microsatellites (n = 119). The mtCR sequence revealed 19 haplotypes, with overall haplotype and nucleotide diversities of 0.74 (±0.027) and 0.0034 (±0.0019), respectively, whereas the nuclear microsatellite observed and expected heterozygosities were 0.408 and 0.421, respectively. There was significant population...
The Nassau grouper (Epinephelus striatus) has sustained large declines across its distribution, i... more The Nassau grouper (Epinephelus striatus) has sustained large declines across its distribution, including extirpation of many of its fish spawning aggregations (FSAs). Within US Virgin Islands (USVI) waters, Nassau grouper FSAs were overfished until their disappearance in the 1970s and 1980s. In the early 2000s, however, Nassau grouper were found gathering at Grammanik Bank, USVI, a mesophotic coral reef adjacent to one of the extinct aggregation sites, and regulatory protective measures were implemented to protect this fledgling FSA. The population genetic dynamics of this rapid FSA deterioration followed by protection-facilitated, incipient recovery are unknown. We addressed two objectives: (1) we explored which factors (i.e., local vs. external recruitment) might be key in shaping the USVI FSA recovery; and (2) we examined the consequences of severe past overfishing on this FSA’s current genetic status. We genotyped individuals (15 microsatellites) from the USVI FSA comprising three successive spawning years (2008–2010), as well as individuals from a much larger, presumably less impacted, Nassau grouper FSA in the Cayman Islands, to assess their comparative population dynamics. No population structure was detected between the USVI and Cayman FSAs (FST = −0.0004); however, a temporally waning, genetic bottleneck signal was detected in the USVI FSA. Parentage analysis failed to identify any parent–offspring matches between USVI FSA adults and nearby juveniles, and relatedness analysis showed low levels of genetic relatedness among USVI FSA individuals. Genetic diversity across USVI FSA temporal collections was relatively high, and no marked differences were found between the USVI and Cayman FSAs. These collective results suggest that external recruitment is an important driver of the USVI FSA recovery. Furthermore, despite an apparent genetic bottleneck, the genetic diversity of USVI Nassau grouper has not been severely compromised. Our findings also provide a baseline for future genetic monitoring of the nascent USVI aggregation.
Knowledge of genetic connectivity dynamics in the world's large-bodied, highly migratory, ape... more Knowledge of genetic connectivity dynamics in the world's large-bodied, highly migratory, apex predator sharks across their global ranges is limited. One such species, the tiger shark (Galeocerdo cuvier), occurs worldwide in warm temperate and tropical waters, uses remarkably diverse habitats (nearshore to pelagic) and possesses a generalist diet that can structure marine ecosystems through top-down processes. We investigated the phylogeography and the global population structure of this exploited, phylogenetically enigmatic shark by using 10 nuclear microsatellites (n = 380) and sequences from the mitochondrial control region (CR, n = 340) and cytochrome oxidase I gene (n = 100). All three marker classes showed the genetic differentiation between tiger sharks from the western Atlantic and Indo-Pacific ocean basins (microsatellite FST > 0.129; CR ΦST > 0.497), the presence of North vs. southwestern Atlantic differentiation and the isolation of tiger sharks sampled from H...
Overfishing is a primary cause of population declines for many shark species of conservation conc... more Overfishing is a primary cause of population declines for many shark species of conservation concern. However, means of obtaining information on fishery interactions and mortality, necessary for the development of successful conservation strategies, are often fishery-dependent and of questionable quality for many species of commercially exploited pelagic sharks. We used satellite telemetry as a fisheries-independent tool to document fisheries interactions, and quantify fishing mortality of the highly migratory shortfin mako shark (<i>Isurus oxyrinchus</i>) in the western North Atlantic Ocean. Forty satellite-tagged shortfin mako sharks tracked over 3 years entered the Exclusive Economic Zones of 19 countries and were harvested in fisheries of five countries, with 30% of tagged sharks harvested. Our tagging-derived estimates of instantaneous fishing mortality rates (<i>F</i> = 0.19–0.56) were 10-fold higher than previous estimates from fisheries-dependent data (approx. 0.015–0.024), suggesting data used in stock assessments may considerably underestimate fishing mortality. Additionally, our estimates of <i>F</i> were greater than those associated with maximum sustainable yield, suggesting a state of overfishing. This information has direct application to evaluations of stock status and for effective management of populations, and thus satellite tagging studies have potential to provide more accurate estimates of fishing mortality and survival than traditional fishery-dependent methodology.
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