Distribution patterns and population structure of the blue shark (Prionace glauca) in the Atlantic and Indian Oceans

The blue shark (Prionace glauca) is the most frequently captured shark in pelagic oceanic fisheries, especially pelagic longlines targeting swordfish and/or tunas. As part of cooperative scientific efforts for fisheries and biological data collection, information from fishery observers, scientific projects and surveys, and from recreational fisheries from several nations in the Atlantic and Indian Oceans was compiled. Data sets included information on location, size and sex, in a total of 478,220 blue shark records collected between 1966 and 2014. Sizes ranged from 36 to 394 cm fork length. Considerable variability was observed in the size distribution by region and season in both oceans. Larger blue sharks tend to occur in equatorial and tropical regions, and smaller specimens in higher latitudes in temperate waters. Differences in sex ratios were also detected spatially and seasonally. Nursery areas in the Atlantic seem to occur in the temperate south-east off South Africa and Namibia, in the south-west off southern Brazil and Uruguay, and in the north-east off the Iberian Peninsula and the Azores. Parturition may occur in the tropical north-east off West Africa. In the Indian Ocean, nursery areas also seem to occur in temperate waters, especially in the south-west Indian Ocean off South Africa, and in the south-east off south-western Australia. The distributional patterns presented in this study provide a better understanding of how blue sharks segregate by size and sex, spatially and temporally, and improve the scientific advice to help adopt more informed and efficient management and conservation measures for this cosmopolitan species.Postprin

Age and growth of the blue shark (Prionace glauca) in the Indian Ocean

Since there is still a lack of biological information regarding Prionace glauca in the Indian Ocean, specifically in terms of age estimation and growth modelling, the age and growth of this species was studied by analysing vertebral samples. All samples were collected from specimens captured by pelagic longliners between March 2013 and September 2016, with sizes ranging from 82 to 301 cm fork length (LF). Two growth models were fitted to the age data, a three-parameter von Bertalanffy growth function (VBGF) re-parameterized to calculate L0 (size at birth) and a two-parameter VBGF with a fixed L0. The latter was considered the most adequate to describe the growth of the species, with the estimated parameters being L∞ = 283.8 cm LF, k  = 0.13 year−1 for males and L∞ = 290.6 cm LF, k = 0.12 year−1 for females. These results suggest that females have a slower growth than males. The maximum age estimated was 25 years, representing the oldest attributed age to this species so far. Further work is needed regarding P. glauca in the Indian Ocean, but this study adds important life-history information that can contribute for the management and conservation of the species.IF/00253/2014) from the Portuguese Foundation for Science and Technologyinfo:eu-repo/semantics/publishedVersio

Habitat partitioning and vulnerability of sharks in the Great Barrier Reef Marine Park

Sharks present a critical conservation challenge, but little is known about their spatial distribution and vulnerability, particularly in complex seascapes such as Australia's Great Barrier Reef Marine Park (GBRMP). We review (1) the distribution of shark species among the primary habitats of the GBRMP (coral reefs, inshore/shelf, pelagic and deep-water habitats) (2) the relative exploitation of each species by fisheries, and (3) how current catch rates interact with their vulnerability and trophic index. Excluding rays and chimaeras, we identify a total of 82 shark species in the GBRMP. We find that shark research in the GBRMP has yielded little quantitative information on most species. Reef sharks are largely site-fidelic, but can move large distances and some regularly use non-reef habitats. Inshore and shelf sharks use coastal habitats either exclusively or during specific times in their life cycle (e.g. as nurseries). Virtually nothing is known about the distribution and habitat use of the GBRMP's pelagic and deep-water sharks. At least 46 species (53.5 %) are caught in one or more fisheries, but stock assessments are lacking for most. At least 17 of the sharks caught are considered highly vulnerable to exploitation. We argue that users of shark resources should be responsible for demonstrating that a fishery is sustainable before exploitation is allowed to commence or continue. This fundamental change in management principle will safeguard against stock collapses that have characterised many shark fisheries

TRAITS LIFE AND TROPHIC ONTOGENY OF TWO SPECIES: THE BLUE SHARK, PRIONACE GLAUCA AND THE SILKY SHARK, CARCHARHINUS FALCIFORMIS, IN THE SOUTH WEST INDIAN OCEAN

participantSharks were considered as top level predators in most marine ecosystems and had a key role because they controled the community structure and the ecosystem process. 700.000 to 850.000 tons of sharks were captured worldwide and this quantity is probably underestimated. Accidental capture in industrial fishing, on purse seine or on longliner, the total shark captured was badly known and underestimated because the carcass were discharged dead or alive after practicing shark fining. In additional, landings were not mentioned on logbooks and the number of observatory program was very limited. These situations may distort stock evaluation and conduct to a lack of accurate biological data and reliable statistics. The blue and the silky shark, taken into account in this study are the main accidental bycatch of the industrial fisheries. Sharks in general, supported badly the overexploitation and the knowledge on their biology, their ecology, and the demographic structures were cruelly far away from the knowledge which deserves such indispensable functional group in the oceanic ecosystems. This research consists of determining the various preys and the evolution of the diet of these two species over its lifetime through the analysis of the stable isotopes 13C and 15N in tissues and vertebras. The life history of these populations will be determined (growth-age relation, size at 1st sexual maturity, fertility and number of embryos). Then, intra and interspecific comparison of the life history traits and the feeding ecology was realized. Associated with a demographic analysis of the populations, they will allow estimating the current abundance of these two species

TRAITS LIFE AND TROPHIC ONTOGENY OF TWO SPECIES: THE BLUE SHARK, PRIONACE GLAUCA AND THE SILKY SHARK, CARCHARHINUS FALCIFORMIS, IN THE SOUTH WEST INDIAN OCEAN

participantSharks were considered as top level predators in most marine ecosystems and had a key role because they controled the community structure and the ecosystem process. 700.000 to 850.000 tons of sharks were captured worldwide and this quantity is probably underestimated. Accidental capture in industrial fishing, on purse seine or on longliner, the total shark captured was badly known and underestimated because the carcass were discharged dead or alive after practicing shark fining. In additional, landings were not mentioned on logbooks and the number of observatory program was very limited. These situations may distort stock evaluation and conduct to a lack of accurate biological data and reliable statistics. The blue and the silky shark, taken into account in this study are the main accidental bycatch of the industrial fisheries. Sharks in general, supported badly the overexploitation and the knowledge on their biology, their ecology, and the demographic structures were cruelly far away from the knowledge which deserves such indispensable functional group in the oceanic ecosystems. This research consists of determining the various preys and the evolution of the diet of these two species over its lifetime through the analysis of the stable isotopes 13C and 15N in tissues and vertebras. The life history of these populations will be determined (growth-age relation, size at 1st sexual maturity, fertility and number of embryos). Then, intra and interspecific comparison of the life history traits and the feeding ecology was realized. Associated with a demographic analysis of the populations, they will allow estimating the current abundance of these two species

Thiol- and Biotin-Labeled Probes for Oligonucleotide Quartz Crystal Microbalance Biosensors of Microalga Alexandrium Minutum

Two quartz crystal microbalance oligonucleotide biosensors of a toxic microalga gene sequence (Alexandrium Minutum) have been designed. Grafting on a gold surface of 20-base thiol- or biotin-labeled probe, and selective hybridization with the complementary 20-base target, have been monitored in situ with a 27 MHz quartz crystal microbalance under controlled hydrodynamic conditions. The frequency of the set up is stable to within a few hertz, corresponding to the nanogram scale, for three hour experiments. DNA recognition by the two biosensors is efficient and selective. Hybridization kinetic curves indicate that the biosensor designed with the thiol-labeled probe is more sensitive, and that the biosensor designed with the biotin-labeled probe has a shorter time response and a higher hybridization efficiency

Isotopic niches of the blue shark Prionace glauca and the silky shark Carcharhinus falciformis in the southwestern Indian Ocean

In the Indian Ocean, the blue shark Prionace glauca and the silky shark Carcharhinus falciformis represent the 2 main shark bycatch species in pelagic longline and purse seine fisheries, respectively. With the increasing market demand for fins, catches may increase in the future, with potential effects on ecosystem trophic functioning through top-down cascading effects. Knowledge of the species' trophic ecology is therefore crucial but is limited by the lack of data from the Indian Ocean. Stable isotope analysis was therefore performed on muscle tissues (δ15N and δ13C) of these 2 shark species from the western Indian Ocean. Our study showed that body length, season, and zone effects were relatively small for the 2 species. However, significant δ13C differences between the 2 species suggest niche partitioning, with silky sharks having a more inshore foraging habitat than blue sharks. Finally, lower muscle δ15N values were observed in juvenile silky sharks caught by purse seiners around fish aggregating devices (FADs) compared to juveniles caught by longliners. One hypothesis is that FADs could act as an ecological trap for juvenile silky sharks, leading to a position at lowest trophic level for these individuals. However, different foraging habitats could also explain the observed patterns between juveniles. Although preliminary, our results provide a basis for the implementation of species-specific protection and management strategies

DNA hybridization mechanism in an interfacial environment: What hides beneath first order k (s(-1)) kinetic constant?

The scientific question addressed in this work is: what hides beneath first order kinetic constant k (s(-1)) measured for hybridization of a DNA target on a biosensor surface. Kinetics hybridization curves were established with a 27 MHz quartz microbalance (9 MHz, third harmonic) biosensor, constituted of a 20-base probe monolayer deposited on a gold covered quartz surface. Kinetics analysis, by a known two-step adsorption-hybridization mechanism, is well appropriate to fit properly hybridization kinetics curves, for complementary 20-base to 40-base targets over two concentration decades. It was found that the K-1 (M-1) adsorption constant, relevant to the first step, concerns an equilibrium between non hybridized targets and hybridized pre-complex and increases with DNA target length. It was established that k(2) (s(-1)), relevant to irreversible formation of a stable duplex, varies in an opposite way to K-1 with DNA target length. (C) 2012 Published by Elsevier B.V