Oceanic Shark Research Articles

High connectivity on a global scale in the pelagic wahoo, Acanthocybium solandri (tuna family Scombridae)

The population genetic structure and phylogeography of wahoo, Acanthocybium solandri, were investigated on a global scale with intron six of lactate dehydrogenase-A (ldhA6, 8 locations, N = 213) and mtDNA cytochrome b (Cytb, 10 locations, N = 322). Results show extensive sharing of haplotypes across the wahoo's entire global range, and analyses were unable to detect significant structure (nuclear F(ST) = 0.0125, P = 0.106; mtDNA Phi(ST) < 0.0001, P = 0.634). Power analyses indicated 95% confidence in detecting nuclear F(ST) > or = 0.0389 and mtDNA Phi(ST) > or = 0.0148. These findings appear unique, as most other tunas, billfishes, and oceanic sharks exhibit significant population structure on the scale of East-West Atlantic, Atlantic vs. Indian-Pacific, or East-West Pacific. Overall nuclear heterozygosity (H = 0.714) and mtDNA haplotype diversity (h = 0.918) are both high in wahoo, while overall mtDNA nucleotide diversity (pi = 0.006) and nuclear nucleotide diversity (pi = 0.004) are uniformly low, indicating a recent increase in population size. Coalescence analyses yield an estimate of effective female population size (NeF) at approximately 816,000, and a population bottleneck approximately 690,000 years ago. However, conclusions about population history from our Cytb data set are not concordant with a control region survey, a finding that will require further investigation. This is the first example of a vertebrate with a single globally distributed population, a finding we attribute to extensive dispersal at all life stages. The indications of a worldwide stock for wahoo reinforce the mandate for international cooperation on fisheries issues.

Foundations of the method of dating global fluctuations of abundance of oceanic sharks on the basis of the amount of fossil teeth in bottom sediments

A method for dating fluctuations in abundance of Elasmobranchii based on three parameters: density of fossil teeth on the ocean floor, density of modern species, and the rate of teeth replacement in modern species is proposed. As a model event, the substitution by the blue shark Prionace glauca of sharks of the genus Isurus that dominated from the Pliocene to the Late Holocene was used. It was determined that, at various values of the aforementioned parameters, the blue shark occupied a dominant position in the eastern Pacific between 302 and 3940 years ago. It is suggested that, in case of a large amount of material in geological collections using this method, a great number of paleoreconstructions of the development and changes in the oceanic biota may be carried out.

Characterization of osteocalcin (BGP) and matrix Gla protein (MGP) fish specific antibodies: validation for immunodetection studies in lower vertebrates.

In fish species the basic mechanisms of bone development and bone remodeling are not fully understood. The classification of bone tissue in teleosts as cellular or acellular and the presence of transitional states between bone and cartilage and the finding of different types of cartilage in teleosts not previously recognized in higher vertebrates emphasizes the need for a study on the accumulation of the Gla-containing proteins MGP and BGP at the cellular level. In the present study, polyclonal antibodies developed against BGP and MGP from A. regius (a local marine teleost fish) and against MGP from G. galeus (a Pacific Ocean shark), were tested by Western blot for their specificity against BGP and MGP from several other species of teleost fish and shark. For this purpose we extracted and purified both proteins from various marine and freshwater teleosts, identified them by N-terminal amino acid sequence analysis and confirmed the presence of gamma-carboxylation in the proteins with the use of a stain specific for Gla residues. Each antibody recognized either BGP or MGP with no cross-reaction between proteins detected. All purified fish BGPs and MGPs tested were shown to be specifically recognized, thus validating the use of these antibodies for further studies.

Collapse and conservation of shark populations in the Northwest Atlantic.

Overexploitation threatens the future of many large vertebrates. In the ocean, tunas and sea turtles are current conservation concerns because of this intense pressure. The status of most shark species, in contrast, remains uncertain. Using the largest data set in the Northwest Atlantic, we show rapid large declines in large coastal and oceanic shark populations. Scalloped hammerhead, white, and thresher sharks are each estimated to have declined by over 75% in the past 15 years. Closed-area models highlight priority areas for shark conservation, and the need to consider effort reallocation and site selection if marine reserves are to benefit multiple threatened species.

The liver lipid fatty acid profiles of seven Indian Ocean shark species

We have assessed the fatty acid profiles of the livers from seven shark species (Carcharias taurus (raggedtooth/grey nurse), Carcharhinus limbatus (blacktip), Carcharhinus obscurus (dusky), Carcharhinus leucas (Zambezi/bull), Sphyrna lewini (scalloped hammerhead), Carcharhinus brevipinna (spinner), and Galeocerdo cuvieri (tiger)) found off the east coast of South Africa. While there was generally little variation between the species, Carcharias taurus showed fatty acid profiles that would be most favourable in human nutrition, in that it showed both low saturated (SFA) (37.1%) and high polyunsaturated fatty acid (PUFA) (26.6%) levels. However, all species showed profiles rich in PUFA, thus utilising the liver oil from sharks caught as part of the bycatch when fishing for teleost species would avoid unnecessary wastage of a potentially valuable resource.

Quantification and determination of enantiomeric ratios of chiral PCB 95, PCB 132, and PCB 149 in shark liver samples (C. coelolepis) from the Atlantic Ocean

AbstractChiral 2,2′,3,5′,6‐pentachlorobiphenyl (PCB 95), 2,2′,3,3′,4,6′‐hexachlorobiphnyl (PCB 132) and 2,2′,3,4′,5′,6‐hexachlorobiphenyl (PCB 149) were quantified in Atlantic Ocean shark liver samples (C. coelolepis) by gas chromatography‐mass spectrometry (GC‐MS) and their enantiomeric ratios were studied by multidimensional gas chromatography (MDGC) with an achiral‐chiral column combination and detected by ECD and MS/SIM. The concentration range of the chiral PCBs was from 2 to 6 ng/g (fresh weight), which represents 2–6 % of the total PCB mean concentration. The investigations revealed a small enantiomeric bias of PCB 132 in most of the samples studied (ER = 0.75–0.89, ee = 6–14%), while PCB 95 and PCB 149 were present in racemic or almost racemic form.