The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform

Denise Griffing - One of the best experts on this subject based on the ideXlab platform.

  • decrease in sightings of Sixgill Sharks hexanchus griseus in elliott bay seattle wa united states a comparison between 2003 2005 and 2008 2015
    Frontiers in Marine Science, 2019
    Co-Authors: Denise Griffing, Jeff Christiansen, Joel Hollander, Tim E Carpenter, Shawn D. Larson
    Abstract:

    The Bluntnose Sixgill Shark, Hexanchus griseus, is a large predatory Shark, has a worldwide distribution and is listed as near-threatened by the International Union of Conservation of Nature (IUCN). The Seattle Aquarium collected observations of free-swimming Sixgill Sharks in Elliott Bay, Washington, under the aquarium’s pier in 20 m of water from 2003 to 2005 and again from 2008 to 2015 using the same methodology. Compared to total Sixgill sightings between 2003-2005 (273) fewer total Sixgills were sighted at the aquarium’s research station between 2008-2015 (33). The reason for the observed decline in sightings in unknown but based on data from other studies on Sixgills in Puget Sound during the same timeperiod the authors hypothesize the decrease may be due to natural variability of juvenile Sixgill recruitment to Elliott Bay.

  • Decrease in Sightings of Sixgill Sharks, Hexanchus griseus, in Elliott Bay, Seattle, WA, United States, a Comparison Between 2003–2005 and 2008–2015
    'Frontiers Media SA', 2019
    Co-Authors: Denise Griffing, Jeff Christiansen, Joel Hollander, Tim Carpenter, Shawn Larson
    Abstract:

    The Bluntnose Sixgill Shark, Hexanchus griseus, is a large predatory Shark, has a worldwide distribution and is listed as near-threatened by the International Union of Conservation of Nature (IUCN). The Seattle Aquarium collected observations of free-swimming Sixgill Sharks in Elliott Bay, Washington, under the aquarium’s pier in 20 m of water from 2003 to 2005 and again from 2008 to 2015 using the same methodology. Compared to total Sixgill sightings between 2003 and 2005 (273) fewer total Sixgills were sighted at the aquarium’s research station between 2008 and 2015 (33). The reason for the observed decline in sightings in unknown but based on data from other studies on Sixgills in Puget Sound during the same timeperiod the authors hypothesize the decrease may be due to natural variability of juvenile Sixgill recruitment to Elliott Bay

  • observations on abundance of Bluntnose Sixgill Sharks hexanchus griseus in an urban waterway in puget sound 2003 2005
    PLOS ONE, 2014
    Co-Authors: Denise Griffing, Shawn D. Larson, Jeff Christiansen, Joel Hollander, Tim E Carpenter, Charles R Doss
    Abstract:

    The Bluntnose Sixgill Shark, Hexanchus griseus, is a widely distributed but poorly understood large, apex predator. Anecdotal reports of diver-Shark encounters in the late 1990’s and early 2000’s in the Pacific Northwest stimulated interest in the normally deep-dwelling Shark and its presence in the shallow waters of Puget Sound. Analysis of underwater video documenting Sharks at the Seattle Aquarium’s Sixgill research site in Elliott Bay and mark-resight techniques were used to answer research questions about abundance and seasonality. Seasonal changes in relative abundance in Puget Sound from 2003–2005 are reported here. At the Seattle Aquarium study site, 45 Sixgills were tagged with modified Floy visual marker tags, along with an estimated 197 observations of untagged Sharks plus 31 returning tagged Sharks, for a total of 273 Sixgill observations recorded. A mark-resight statistical model based on analysis of underwater video estimated a range of abundance from a high of 98 Sharks seen in July of 2004 to a low of 32 Sharks seen in March of 2004. Both analyses found Sixgills significantly more abundant in the summer months at the Seattle Aquarium’s research station.

  • Relatedness and polyandry of Sixgill Sharks, Hexanchus griseus, in an urban estuary
    Conservation Genetics, 2011
    Co-Authors: Shawn Larson, Dayv Lowry, Jeff Christiansen, Denise Griffing, Jimiane Ashe, Kelly Andrews
    Abstract:

    The Bluntnose Sixgill Shark ( Hexanchus griseus ) is a widely distributed species found in tropical and temperate waters of every ocean, yet we know relatively little about their basic biology including their life history and population structure. From 2003–2007, we collected over 300 biopsy samples from Sixgills during research operations in Puget Sound, WA, USA. Genotypic data using ten polymorphic microsatellites were used to describe Sixgill genetic diversity, relatedness and mating pattern. Diversity within Sixgills was found to be moderate with an average observed heterozygosity of 0.45, an average expected heterozygosity of 0.61, an average of 12 alleles per locus, and an average allelic richness of eight within microsatellite loci. Our data suggests all of the sampled individuals come from one intermixing population, and we found no historical evidence of significant population bottlenecks. Many of the Sharks were sampled using longline techniques with several Sharks captured at the same time and place. Similarly, multiple Sharks were sampled on several occasions during research events at the Seattle Aquarium. The proportion of individuals that were full- or half-siblings was high among Sharks sampled at the same time and place (range 0.65–0.87). Analysis of the genetic relationship between one large female washed ashore and 71 of her near-term pups suggested a polyandrous mating system with as many as nine males contributing to her offspring. This study is the first to investigate genetic diversity, relatedness and paternity within Sixgill Sharks and sheds light on important conservation implications for this little known Shark population.

Jeff Christiansen - One of the best experts on this subject based on the ideXlab platform.

  • decrease in sightings of Sixgill Sharks hexanchus griseus in elliott bay seattle wa united states a comparison between 2003 2005 and 2008 2015
    Frontiers in Marine Science, 2019
    Co-Authors: Denise Griffing, Jeff Christiansen, Joel Hollander, Tim E Carpenter, Shawn D. Larson
    Abstract:

    The Bluntnose Sixgill Shark, Hexanchus griseus, is a large predatory Shark, has a worldwide distribution and is listed as near-threatened by the International Union of Conservation of Nature (IUCN). The Seattle Aquarium collected observations of free-swimming Sixgill Sharks in Elliott Bay, Washington, under the aquarium’s pier in 20 m of water from 2003 to 2005 and again from 2008 to 2015 using the same methodology. Compared to total Sixgill sightings between 2003-2005 (273) fewer total Sixgills were sighted at the aquarium’s research station between 2008-2015 (33). The reason for the observed decline in sightings in unknown but based on data from other studies on Sixgills in Puget Sound during the same timeperiod the authors hypothesize the decrease may be due to natural variability of juvenile Sixgill recruitment to Elliott Bay.

  • Decrease in Sightings of Sixgill Sharks, Hexanchus griseus, in Elliott Bay, Seattle, WA, United States, a Comparison Between 2003–2005 and 2008–2015
    'Frontiers Media SA', 2019
    Co-Authors: Denise Griffing, Jeff Christiansen, Joel Hollander, Tim Carpenter, Shawn Larson
    Abstract:

    The Bluntnose Sixgill Shark, Hexanchus griseus, is a large predatory Shark, has a worldwide distribution and is listed as near-threatened by the International Union of Conservation of Nature (IUCN). The Seattle Aquarium collected observations of free-swimming Sixgill Sharks in Elliott Bay, Washington, under the aquarium’s pier in 20 m of water from 2003 to 2005 and again from 2008 to 2015 using the same methodology. Compared to total Sixgill sightings between 2003 and 2005 (273) fewer total Sixgills were sighted at the aquarium’s research station between 2008 and 2015 (33). The reason for the observed decline in sightings in unknown but based on data from other studies on Sixgills in Puget Sound during the same timeperiod the authors hypothesize the decrease may be due to natural variability of juvenile Sixgill recruitment to Elliott Bay

  • observations on abundance of Bluntnose Sixgill Sharks hexanchus griseus in an urban waterway in puget sound 2003 2005
    PLOS ONE, 2014
    Co-Authors: Denise Griffing, Shawn D. Larson, Jeff Christiansen, Joel Hollander, Tim E Carpenter, Charles R Doss
    Abstract:

    The Bluntnose Sixgill Shark, Hexanchus griseus, is a widely distributed but poorly understood large, apex predator. Anecdotal reports of diver-Shark encounters in the late 1990’s and early 2000’s in the Pacific Northwest stimulated interest in the normally deep-dwelling Shark and its presence in the shallow waters of Puget Sound. Analysis of underwater video documenting Sharks at the Seattle Aquarium’s Sixgill research site in Elliott Bay and mark-resight techniques were used to answer research questions about abundance and seasonality. Seasonal changes in relative abundance in Puget Sound from 2003–2005 are reported here. At the Seattle Aquarium study site, 45 Sixgills were tagged with modified Floy visual marker tags, along with an estimated 197 observations of untagged Sharks plus 31 returning tagged Sharks, for a total of 273 Sixgill observations recorded. A mark-resight statistical model based on analysis of underwater video estimated a range of abundance from a high of 98 Sharks seen in July of 2004 to a low of 32 Sharks seen in March of 2004. Both analyses found Sixgills significantly more abundant in the summer months at the Seattle Aquarium’s research station.

  • Relatedness and polyandry of Sixgill Sharks, Hexanchus griseus, in an urban estuary
    Conservation Genetics, 2011
    Co-Authors: Shawn Larson, Dayv Lowry, Jeff Christiansen, Denise Griffing, Jimiane Ashe, Kelly Andrews
    Abstract:

    The Bluntnose Sixgill Shark ( Hexanchus griseus ) is a widely distributed species found in tropical and temperate waters of every ocean, yet we know relatively little about their basic biology including their life history and population structure. From 2003–2007, we collected over 300 biopsy samples from Sixgills during research operations in Puget Sound, WA, USA. Genotypic data using ten polymorphic microsatellites were used to describe Sixgill genetic diversity, relatedness and mating pattern. Diversity within Sixgills was found to be moderate with an average observed heterozygosity of 0.45, an average expected heterozygosity of 0.61, an average of 12 alleles per locus, and an average allelic richness of eight within microsatellite loci. Our data suggests all of the sampled individuals come from one intermixing population, and we found no historical evidence of significant population bottlenecks. Many of the Sharks were sampled using longline techniques with several Sharks captured at the same time and place. Similarly, multiple Sharks were sampled on several occasions during research events at the Seattle Aquarium. The proportion of individuals that were full- or half-siblings was high among Sharks sampled at the same time and place (range 0.65–0.87). Analysis of the genetic relationship between one large female washed ashore and 71 of her near-term pups suggested a polyandrous mating system with as many as nine males contributing to her offspring. This study is the first to investigate genetic diversity, relatedness and paternity within Sixgill Sharks and sheds light on important conservation implications for this little known Shark population.

Shawn Larson - One of the best experts on this subject based on the ideXlab platform.

  • Decrease in Sightings of Sixgill Sharks, Hexanchus griseus, in Elliott Bay, Seattle, WA, United States, a Comparison Between 2003–2005 and 2008–2015
    'Frontiers Media SA', 2019
    Co-Authors: Denise Griffing, Jeff Christiansen, Joel Hollander, Tim Carpenter, Shawn Larson
    Abstract:

    The Bluntnose Sixgill Shark, Hexanchus griseus, is a large predatory Shark, has a worldwide distribution and is listed as near-threatened by the International Union of Conservation of Nature (IUCN). The Seattle Aquarium collected observations of free-swimming Sixgill Sharks in Elliott Bay, Washington, under the aquarium’s pier in 20 m of water from 2003 to 2005 and again from 2008 to 2015 using the same methodology. Compared to total Sixgill sightings between 2003 and 2005 (273) fewer total Sixgills were sighted at the aquarium’s research station between 2008 and 2015 (33). The reason for the observed decline in sightings in unknown but based on data from other studies on Sixgills in Puget Sound during the same timeperiod the authors hypothesize the decrease may be due to natural variability of juvenile Sixgill recruitment to Elliott Bay

  • Relatedness and polyandry of Sixgill Sharks, Hexanchus griseus, in an urban estuary
    Conservation Genetics, 2011
    Co-Authors: Shawn Larson, Dayv Lowry, Jeff Christiansen, Denise Griffing, Jimiane Ashe, Kelly Andrews
    Abstract:

    The Bluntnose Sixgill Shark ( Hexanchus griseus ) is a widely distributed species found in tropical and temperate waters of every ocean, yet we know relatively little about their basic biology including their life history and population structure. From 2003–2007, we collected over 300 biopsy samples from Sixgills during research operations in Puget Sound, WA, USA. Genotypic data using ten polymorphic microsatellites were used to describe Sixgill genetic diversity, relatedness and mating pattern. Diversity within Sixgills was found to be moderate with an average observed heterozygosity of 0.45, an average expected heterozygosity of 0.61, an average of 12 alleles per locus, and an average allelic richness of eight within microsatellite loci. Our data suggests all of the sampled individuals come from one intermixing population, and we found no historical evidence of significant population bottlenecks. Many of the Sharks were sampled using longline techniques with several Sharks captured at the same time and place. Similarly, multiple Sharks were sampled on several occasions during research events at the Seattle Aquarium. The proportion of individuals that were full- or half-siblings was high among Sharks sampled at the same time and place (range 0.65–0.87). Analysis of the genetic relationship between one large female washed ashore and 71 of her near-term pups suggested a polyandrous mating system with as many as nine males contributing to her offspring. This study is the first to investigate genetic diversity, relatedness and paternity within Sixgill Sharks and sheds light on important conservation implications for this little known Shark population.

Baldó F. - One of the best experts on this subject based on the ideXlab platform.

  • Results on main elasmobranches species from 2001 to 2020 Porcupine Bank (NE Atlantic) bottom trawl surveys
    Centro Oceanográfico de Cádiz, 2021
    Co-Authors: Fernández-zapico O., Ruiz-pico S., Velasco F., Blanco M., Rodríguez-cabello C., Baldó F.
    Abstract:

    This working document presents the results of the most significant elasmobranch species caught on the Porcupine Spanish Groundfish Survey (SP-PORC-Q3) in 2020. Biomass, abundance, distribution and length frequency were analysed for Galeus melastomus (blackmouth catShark), Deania calcea (birdbeak dogfish), Deania profundorum (arrowhead dogfish), Scymnodon ringens (knifetooth dogfish), Scyliorhinus canicula (lesser spotted dogfish), Etmopterus spinax (velvet belly lantern Shark), Dalatias licha (kitefin Shark), Hexanchus griseus (Bluntnose Sixgill Shark), Dipturus nidarosiensis (Norwegian skate), Dipturus batis (common skate), Dipturus intermedius (common skate), Leucoraja circularis (sandy ray) and Leucoraja naevus (cuckoo ray), Squalus acanthias (picked dogfish) and Raja clavata (thornback ray). In 2020 the biomass of D. calcea, S. ringens, D. nidarosiensis, H. griseus and D. licha increased, whereas it decreased for G. melastomus, S. canicula, E. spinax and L. circularis. Signs of recruitment were found for S. ringens and E. spinax. Only a few specimens of S. acanthias, D. profundorum, R. clavata, D. batis, L. naevus and D. intermedius were captured. The species R. montagui, with regular presence in the historical series, was not found in 2020 survey

  • Results on main elasmobranch species captured during the 2001-2014 Porcupine Bank (NE Atlantic) bottom trawl surveys
    Centro Oceanográfico de Santander, 2015
    Co-Authors: Fernández-zapico O., Baldó F., Velasco F., Rodríguez-cabello-ródenas, M.c. Cristina), Ruiz-pico S.
    Abstract:

    This working document presents the results on the most significant elasmobranch species of the Porcupine Bank Spanish surveys in 2014 and updates the documents presented in previous years with the information in the whole historical series from 2001. The main species in biomass terms in this survey were Galeus melastomus (blackmouth catShark), Deania calcea (birdbeak dogfish), Scymnodon ringens (Knifetooth dogfish), Dipturus nidarosiensis (Norwegian skate), Scyliorhinus canicula (lesser spotted dogfish), Etmopterus spinax (velvet belly lantern Shark), Hexanchus griseus (Bluntnose Sixgill Shark), Dalatias licha (Kitefin Shark), Leucoraja circularis (sandy ray), Dipturus cf. flossada, Leucoraja naevus (cuckoo ray) and Dipturus cf. intermedia (common skate). Biomass, distribution and length ranges were analysed for these species. All the species analysed increased its biomass in 2014, except S. canicula and D. cf. flossada that decreased. D. calcea individuals smaller than 65 cm were captured again in 2014 after not having been captured the previous year, although catches were very low. Raja brachyura was recorded for the first time in the survey area

  • Results on main elasmobranch species captured during the 2001-2013 Porcupine Bank (NE Atlantic) bottom trawl surveys
    Centro Oceanográfico de Santander, 2014
    Co-Authors: Ruiz-pico S., Velasco F., Baldó F., Rodríguez-cabello-ródenas, M.c. Cristina), Fernández-zapico O.
    Abstract:

    This working document presents the results on the most significant elasmobranch species of the Porcupine Bank Spanish surveys in 2013. The main species in biomass terms in this survey were Galeus melastomus (blackmouth catShark), Deania calcea (birdbeak dogfish), Deania profundorum (arrowhead dogfish), Scyliorhinus canicula (lesser spotted dogfish), Scymnodon ringens (Knifetooth dogfish), Etmopterus spinax (velvet belly lantern Shark), Dalatias licha (Kitefin Shark) Hexanchus griseus (Bluntnose Sixgill Shark), Leucoraja circularis (sandy ray), Leucoraja naevus (cuckoo ray), Dipturus nidarosiensis (Norwegian skate) and Dipturus spp. / Dipturus cf. flossada / Dipturus cf. intermedia (common skate). Biomass, distribution and length ranges were analysed. Many of these species occupy mainly the deep areas covered in the survey, especially D. calcea, D. profundorum and S. ringens

  • Results on main elasmobranch species captured during the 2001-2011 Porcupine Bank (NE Atlantic) bottom trawl surveys
    Centro Oceanográfico de Santander, 2012
    Co-Authors: Ruiz-pico S., Velasco F., Baldó F., Fernández-zapico O., Rodríguez-cabello-ródenas, M.c. Cristina)
    Abstract:

    This working document presents the results on nine of the most important elasmobranch species of the Porcupine bank Spanish surveys during the last decade (2001-2011). The Shark species more abundant in these surveys in biomass terms were blackmouth catShark (Galeus melastomus), birdbeak dogfish (Deania calcea), Knifetooth dogfish (Scymnodon ringens), velvet belly lantern Shark (Etmopterus spinax), lesser spotted dogfish (Scyliorhinus canicula) and Bluntnose Sixgill Shark (Hexanchus griseus); while sandy ray (Leucoraja circularis), cuckoo ray (Leucoraja naevus) and common skate (Dipturus spp. / Dipturus cf. flossada) were the more frequent Rajidae. Biomass, distribution and length ranges were analysed. Many of these species occupy mainly the deep areas covered in the survey, especially D. calcea and S. ringens.Versión del edito

  • Results on main elasmobranch species captured during the 2001-2010 Porcupine Bank (NE Atlantic) bottom trawl surveys
    Centro Oceanográfico de Santander, 2011
    Co-Authors: Fernández-zapico O., Ruiz-pico S., Velasco F., Baldó F., Blanco M.
    Abstract:

    This paper presents the results on nine of the most important elasmobranch fish species of the Porcupine bank Spanish surveys during the last decade (2001-2010). The main species in the captures in decreasing biomass order are: blackmouth catShark, birdbeak dogfish, knifetooth dogfish, velvet belly, lesser spotted dogfish, Bluntnose Sixgill Shark, sandy ray, cuckoo ray and common skate. Manyof these species occupy mainly the deep areas covered in the survey,especially birdbeak dogfish, knifetooth dogfish and velvet belly. Less confined to deeper grounds are blackmouth catShark and sandy ray, while lesser spotted dogfish and cuckoo ray inhabit mainly the shallowergrounds close to the Irish shelf or the central mound in the bank. Length distributions of these species along the survey series are also presented and discussed. The few available data on siki Sharks from the Porcupine bank survey are also summarized.Versión del edito

Hakan Kabasakal - One of the best experts on this subject based on the ideXlab platform.

  • Bluntnose Sixgill Shark hexanchus griseus chondrichthyes hexanchidae caught by commercial fishing vessels in the seas of turkey between 1967 and 2013
    2013
    Co-Authors: Hakan Kabasakal
    Abstract:

    One hundred and fifty specimens of Hexanchus griseus (Bonnaterre, 1788) were caught by commercial fishing vessels in the seas of Turkey, between 16 July 1967 and 4 February 2013. Regarding the number of captured specimens per marine areas, the highest number of captures was recorded in the Sea of Marmara (90 specimens; 60 %), followed by the Aegean (41 specimens; 27.3 %), Mediterranean (15 specimens; 10 %) and Black (3 specimens; 2 %) seas. A single stranded individual was also recorded in the Canakkale Strait. Regarding the number of recorded specimens it is obvious that the Sixgill Shark Data Bank of Turkey holds a significant number of H. griseus specimens caught in the eastern Mediterranean Sea, both reported in historical and contemporary studies. The sex ratio of the examined specimens of H. griseus is 1:2.61 in favour of females. Analysis of the fishing gear used for 72 of 150 examined Sixgill Sharks indicates that the most common fishing gear used to catch H. griseus is purse-seine, followed by several types of bottom fishing gear. Total length of the recorded specimens ranged between 50 and > 650 cm TL for both sexes; however, catches were dominated by two size groups, 250-350 cm and 350-450 cm TL, respectively.

  • on the occurrence of the Bluntnose Sixgill Shark hexanchus griseus chondrichthyes hexanchidae in the sea of marmara
    Marine Biodiversity Records, 2009
    Co-Authors: Hakan Kabasakal
    Abstract:

    Field surveys and literature review revealed the capture of 50 Bluntnose Sixgill Sharks from the Sea of Marmara. Total lengths of the observed specimens ranged from 1.2–6 m, and weighed between 10 and 1000 kg. Nine specimens were males, 23 were females and 18 were of unknown sex. Regarding the bathymetric distribution of the captured Bluntnose Sixgill Sharks, majority of the specimens (78%) were recorded in slope and shelf waters of the eastern and northern Sea of Marmara. Fishing presents the only known proximate threat to Bluntnose Sixgill Shark populations in Marmaric waters. Inclusion of Hexanchus griseus in the endangered marine fish list of the Turkish Fisheries Act, would be the first step before subjecting H. griseus to 100% protection.

  • preliminary observations on the reproductive biology and diet of the Bluntnose Sixgill Shark hexanchus griseus bonnaterre 1788 chondrichthyes hexanchidae in turkish seas
    Acta Adriatica, 2004
    Co-Authors: Hakan Kabasakal
    Abstract:

    A search through field surveys and literature revealed that 39 Bluntnose Sixgill Sharks, Hexanchus griseus, were captured in the Black, Marmara, and Aegean Seas between 1974 and 2003. One of the specimens was captured in the prebosphoric waters of the southwestern Black Sea, 27 in the Sea of Marmara, and 11 in the Aegean Sea. H. griseus is hereby recorded for the first time in the southwestern Black Sea. Available information suggests that H. griseus gives birth from October to the end of February in the northern Aegean and Sea of Marmara. The main prey of the listed Sixgill Sharks were teleosteans.