Assessment of Total and Organic Mercury Levels in Blue Sharks (Prionace glauca) from the South and Southeastern Brazilian Coast

Mercury occurrence was evaluated in samples of edible muscle tissue of 27 blue sharks (Prionace glauca) caught in the Atlantic Ocean, adjacent to the south and southeastern Brazilian coast, indicating a slight increase in comparison with previous data obtained for the same studied area and being higher than those fish caught at different sites of the Atlantic Ocean. Total Hg concentrations ranged from 0.46 to 2.40 mg kg^?1 with the organic Hg fraction ranging between 0.44 and 2.37 mg kg^?1. A negative correlation between total Hg concentration in muscle tissue and blue shark size was obtained, and 40 % of samples analyzed had Hg concentrations higher than 1.0 mg kg^?1 Hg, the maximum concentration permitted in Brazilian predator fish. Data obtained showed that total Hg can be used as a reliable predictor of organic Hg in blue shark muscle because 95 to 98 % of the total Hg measured was found to be organic mercury. The wide range of Hg concentrations obtained for our set of samples can be explained by the heterogeneity of sampled population and the large size of the studied area. Given the adverse toxicological effects of Hg on animals and humans, a regular monitoring program of Hg contamination in Brazilian marine ecosystem can be recommended.     

Isolation of enamelinlike proteins from blue shark (Prionace glauca) enameloid

A sequential dissociative extraction scheme was used to extract proteins from developing Blue Shark enameloid. The first extraction solution (4 M guanidine HC1) solubilized the polypeptides, mainly collagenous, not closely associated with the hydroxyapatite. The next extraction solution (4 M guanidine HC1, 0.5 M ethylenediaminetetraacedic acid (EDTA] solubilized the proteins more closely associated with the tooth mineral component. After extraction, the proteins were separated and isolated with gel electrophoresis. Protein molecular weights were determined and selected proteins were isolated for amino acid composition analysis. The two proteins isolated were tested for mammalian enamel protein antigenic determinants by a "Dot" immunobinding assay. The isolated proteins were enamelinlike by extraction criteria and amino acid composition. Further, the two proteins share antigenic determinants with mammalian enamel proteins.     

Blue shark Prionace glauca fin-to-carcass-mass ratios in Spain and implications for finning ban enforcement

This study examines the processing of fins from blue sharks Prionace glauca caught by the Spanish longline fleet and landed in Vigo, Spain, and implications of these practices for enforcing the E.U. ban on shark finning, which relies on a maximum fin-to-carcass-mass ratio. Two major sources of variability in fin-to-carcass ratios are quantified and discussed: (1) the fin set (type and number of fins retained from each shark) and (2) the cutting method used to separate fins from carcasses. The significant differences in fin-to-carcass-mass ratios between fin sets or cutting procedure demonstrates that the ratio limit is problematic and, conclusively, in order to facilitate proper enforcement, fishermen should be required to land all sharks with the fins still naturally attached to the bodies.     

First evidence of multiple paternity in the blue shark (Prionace glauca)

Multiple paternity (MP) is defined as the behaviour in which females successfully mate with multiple males leading to offspring from different sires within the same litter. MP seems to be frequent and an evolutionary advantage in elasmobranchs. Here the authors report for the first time the occurrence of MP in the cosmopolitan blue shark Prionace glauca L. The evidence, gathered via microsatellite genotyping of pregnant females and their embryos, suggests that MP is very frequent in this species. Knowledge of MP in P. glauca should help describe more precisely its reproductive biology and contribute to the management of its populations.     

Biomagnification of Mercury and Selenium in Blue Shark Prionace glauca from the Pacific Ocean off Mexico

The aim of this study was to determine the biomagnification of mercury through the principal prey of the blue shark, Prionace glauca, off the western coast of Baja California Sur, Mexico, as well as the relationship between mercury and selenium in blue sharks. High levels of mercury were found in shark muscle tissues (1.39?±?1.58?μg/g wet weight); these values are above the allowed 1.0?μg/g for human consumption. The mercury to selenium molar ratio was 1:0.2. We found a low correlation between mercury bioaccumulation and shark size. Juveniles have lower concentrations of mercury than adults. Regarding the analyzed prey, the main prey of the blue shark, pelagic red crab, Pleuroncodes planipes, bioaccumulated 0.04?±?0.01?μg/g Hg wet weight, but the prey with higher bioaccumulation was the bullet fish Auxis spp. (0.20?±?0.02?μg/g wet weight). In terms of volume, the red crab P. planipes can be the prey that provides high levels of mercury to the blue shark.     

On the Capture of a Blue Shark,Prionace glauca (Carcharhinidae), in Peter the Great Bay,Sea of Japan

Journal of Ichthyology - The capture of a blue shark, Prionace glauca, with a body length of 108.5 cm in Peter the Great Bay, Sea of Japan, is reported. Its measurable traits, dental formula, and...     

Development of an alternative ageing technique for blue shark (Prionace glauca) using the vertebra

Accurate determination of age is essential for the comprehensive assessment and management of exploited shark populations. Enhancement of growth bands is necessary to accurately and efficiently determine age. However, most traditional techniques do not describe an efficiency of a series of procedures and the detailed protocol for different‐sized sharks. We describe a simple and highly successful technique for ageing vertebrae of blue shark (Prionace glauca) that we refer to as “burn method”, derived from the “break and burn method” and “shadowing method”—a simple procedure requiring an alkaline treatment to clean the vertebral centra and a burning treatment to enhance growth band visualization. We described optimal times for sharks of precaudal length of 50, 100, 150, and 200 cm as 44.9, 88.7, 134.0, 183.5 s of alkaline treatment, and 6.8, 8.9, 10.2, and 11.5 min of burning treatment; both longer and shorter exposure times resulted in higher failed sample frequencies. Using our burn method, it is possible to do ageing a sample from a wide angle, with the reader able to obtain information on growth bands from different perspectives. To critique different technique efficiencies, the index of average percent error (IAPE) and mean coefficient of variation (CV) are compared for independent readers using the burn method and other techniques (silver nitrate impregnation and the unstained shadowing methods). The precision of the burn method (IAPE, 4.1%; CV, 5.7%) was similar to that of silver nitrate impregnation (IAPE, 5.8%; CV, 8.2%) and unstained shadowing method (IAPE, 8.3%; CV, 11.8%). For younger specimens, the IAPE and CV of the burn method were lower than those of the other techniques, but, compared with other ageing methods, precision decreased for older sharks. We demonstrate that the burn method to be accurate for age determination of blue sharks, especially for specimens with less than 10 bands, but recommend simultaneous use of other methods, such as thin sectioning (the most common for structure‐based ageing) and bomb carbon dating, to accurately determine the age of older individuals.     

Presence of new disulphide-bonded collagens in shark Prionace glauca muscle

• 1.1. Two new collagenous fragments were detected in great blue shark myocommata.
• 2.2. The fragments, isolated from pepsin digests, were shown to be sensitive to disulphide bond cleaving agents. The higher molecular weight fragment (designated HMW) of about 250 kDa gave rise to a 40 kDa fragment following reduction. The second fragment with a molecular weight of about 53 kDa (designated LMW) produced a major fragment of about 29 kDa after reduction with disulphide bond cleaving agents.
• 3.3. Type I collagen, a type I-like collagen and type V collagen were also detected in the myocommata.

     

Morphological abnormalities in a blue shark Prionace glauca (Chondrichthyes: Carcharhinidae) foetus from southern Brazil

This study records the occurrence of a blue shark Prionace glauca foetus, with morphological abnormalities in the trunk and cephalic region, from a female caught by a pelagic longline in October 2003, in southern Brazil.     

Shark (Prionace glauca) elastoidin: characterization of its collagen as [alpha 1(E)]3 homotrimers

A new type of collagen was isolated from elastoidin of great blue shark by limited pepsin digestion. The collagen alpha chain of elastoidin, designated alpha 1(E), was very similar in electrophoretic and chromatographic behavior and amino acid composition to shark skin alpha 1(I) chain, but they were genetically-distinct on the basis of CNBr-peptide maps. The collagen molecule of elastoidin was shown to be an [alpha 1(E)]3 homotrimer.     

A Comparison of the Seasonal Movements of Tiger Sharks and Green Turtles Provides Insight into Their Predator-Prey Relationship

During the reproductive season, sea turtles use a restricted area in the vicinity of their nesting beaches, making them vulnerable to predation. At Raine Island (Australia), the highest density green turtle Chelonia mydas rookery in the world, tiger sharks Galeocerdo cuvier have been observed to feed on green turtles, and it has been suggested that they may specialise on such air-breathing prey. However there is little information with which to examine this hypothesis. We compared the spatial and temporal components of movement behaviour of these two potentially interacting species in order to provide insight into the predator-prey relationship. Specifically, we tested the hypothesis that tiger shark movements are more concentrated at Raine Island during the green turtle nesting season than outside the turtle nesting season when turtles are not concentrated at Raine Island. Turtles showed area-restricted search behaviour around Raine Island for ∼3–4 months during the nesting period (November–February). This was followed by direct movement (transit) to putative foraging grounds mostly in the Torres Straight where they switched to area-restricted search mode again, and remained resident for the remainder of the deployment (53–304 days). In contrast, tiger sharks displayed high spatial and temporal variation in movement behaviour which was not closely linked to the movement behaviour of green turtles or recognised turtle foraging grounds. On average, tiger sharks were concentrated around Raine Island throughout the year. While information on diet is required to determine whether tiger sharks are turtle specialists our results support the hypothesis that they target this predictable and plentiful prey during turtle nesting season, but they might not focus on this less predictable food source outside the nesting season.     

Size and distribution of Pandarus satyrus (Copepoda: Pandaridae) on the blue shark Prionace glauca (Carcharhiniformes: Carcharhinidae) in Costa Rica.

A total of 80 specimens of Pandarus satyrus, a cosmopolitan ectoparasitic copepod, were taken from fishery catches of blue sharks (Prionace glauca) in the Eastern Pacific coast of Costa Rica. All specimens were found in the dorsal surface of pectoral fins (8-30 per shark). Longer specimens were most abundant.     

Distribution of Kroeyerina elongata (Kroyeriidae: Siphonostomatoida, Copepoda) in the olfactory sacs of the blue shark, Prionace glauca

The infection pattern of Kroeyerina elongata (Kroyeriidae, Copepoda) in the olfactory sacs of the blue shark, Prionace glauca, was investigated using 4,722 copepods from 54 olfactory sacs. Copepod prevalence and mean intensity of infection per olfactory sac were 94.0 and 91.1%, respectively, and the most intensely infected olfactory sac and shark hosted 218 and 409 copepods, respectively. There were significant linear relationships between the number of female and total copepods per left olfactory sac and shark fork length as well as between the numbers of female, male, and total copepods per shark and mean olfactory sac width and cumulative olfactory sac width. Female copepods typically outnumbered males within olfactory sacs (mean intensity = 65.7 and 26.3, respectively), and no statistical differences were detected between the numbers of copepods inhabiting the left and right olfactory sacs. Copepods were not evenly distributed within olfactory sacs. Typically, female copepods occupied olfactory chambers located centrally along the length of the olfactory sac, while males infected lateral olfactory chambers nearest the naris. The orientation of most copepods (84.6%) suggested positive rheotaxis relative to the path of water through the olfactory sac. Within olfactory chambers, most mature females (68.2%) infected the first third of the peripheral excurrent channel and the adjacent fringe of olfactory lamellae, while most males (91.7%) infected the olfactory lamellae, and the 4 larval females collected were attached within the lamellar field and grasped by males. Based on the observed infection patterns and the pattern of water flow throughout the olfactory sac, a hypothesis regarding the life cycle of K. elongata is advanced wherein infective copepodids are swept into the olfactory sac from the surrounding sea and initially colonize the olfactory lamellae. Copepodids feed and mature among the olfactory lamellae, and adult males search for mates and copulate with young females among the olfactory lamellae. Inseminated females move to the peripheral excurrent channels to mature and produce ovisacs. Hatching ovisacs release free-swimming nauplii into the excurrent water flow to be swept into the milieu, where they can molt into infective copepodids that may infect new hosts.     

Isolation and characterization of Cu,Zn superoxide dismutase of the shark Prionace glauca

A Cu,Zn superoxide dismutase was purified for the first time from an elasmobranch species (Prionace glauca) and showed the following differences with respect to other animal superoxide dismutases. The enzyme displays a low isoelectric point. The enzyme activity is unusually independent of ionic strength. The isolated enzyme has 30% of its copper in the reduced state.     

New insights on the trophic ecology of blue (Prionace glauca) and shortfin mako sharks (Isurus oxyrinchus) from the oceanic eastern South Pacific

The blue shark (Prionace glauca) and the shortfin mako shark (Isurus oxyrinchus) are two large and highly migratory sharks distributed in most oceans. Although they are often caught in the south Pacific Ocean long-line fisheries, their trophic ecology is poorly understood. Stable isotopes with Bayesian mixing and dependence concentration models were performed to determine the diet and trophic differences between the two species in the South-eastern Pacific Ocean. According to the mixing models, fishes are the most important prey of these sharks. Dolphin calves and remains were found in the stomachs of both species, which represents a novel finding in trophic ecology of South Pacific sharks. Intra-specific differences were found in P. glauca, but not in specimens of I. oxyrinchus. The two sharks showed a high degree of diet overlap (73%), primarily over mackerel and dolphin carcasses. Our results indicate that blue and shortfin mako sharks have a generalist feeding strategy in the eastern Pacific Ocean, with a strong preference for teleost fishes and also for dolphin carcasses. Therefore, trophic studies are useful to understand energy flow through the food web, and the trophic position of key species.     

World without borders—genetic population structure of a highly migratory marine predator,the blue shark (Prionace glauca)

Highly migratory, cosmopolitan oceanic sharks often exhibit complex movement patterns influenced by ontogeny, reproduction, and feeding. These elusive species are particularly challenging to population genetic studies, as representative samples suitable for inferring genetic structure are difficult to obtain. Our study provides insights into the genetic population structure one of the most abundant and wide‐ranging oceanic shark species, the blue shark Prionace glauca, by sampling the least mobile component of the populations, i.e., young‐of‐year and small juveniles (<2 year; N = 348 individuals), at three reported nursery areas, namely, western Iberia, Azores, and South Africa. Samples were collected in two different time periods (2002–2008 and 2012–2015) and were screened at 12 nuclear microsatellites and at a 899‐bp fragment of the mitochondrial control region. Our results show temporally stable genetic homogeneity among the three Atlantic nurseries at both nuclear and mitochondrial markers, suggesting basin‐wide panmixia. In addition, comparison of mtDNA CR sequences from Atlantic and Indo‐Pacific locations also indicated genetic homogeneity and unrestricted female‐mediated gene flow between ocean basins. These results are discussed in light of the species' life history and ecology, but suggest that blue shark populations may be connected by gene flow at the global scale. The implications of the present findings to the management of this important fisheries resource are also discussed.