Deania

Abstract: The sharks and chimaeroids are important members of the deep-water associations of fish of the continental slopes, but little is known about their trophic interactions. The diets of these fish were studied through the deployment of demersal trawls at successive 250 m depth intervals, within a total range of depth of 500 to 2 900 m, in the Rockall Trough to the west of Scotland and Ireland during the period 1975 to 1981. The sharks and chimaeroids, however, only occurred between 500 and 2000 m but principally in the 500 to 1 250 m bathymetric zones. These are the zones of maximum biomass of prey species of fish and probably also of prey species of epibenthos. The sharks divide into 3 trophic groups. Apristurus spp., Centroscymnus crepidater, Ttmopterus spinax and E. princeps exploit micronekton in the vicinity of the sea bed. Centroscyllium fabricii, Centroscymnus coelolepis, Deania calceus and Lepidorhinus squamosus are principally fish eaters. A third group may consist of 2 rarer species in the Rockall Trough, Galeus melastomus and G. murinus that exploit the epibenthos but also, to some extent, the micronekton. The 3 species of chimaeroids (Chimaera monstrosa, Hydrolagus mirabilis and Harriotta raleighana) prey on the epibenthos and the last species may also utilize, to some extent, infaunal species.

Abstract: Life-history parameters of Deania calcea and Deania quadrispinosa suggested that their productivity was very low. Maturity (LT50) occurs at c. 80% of maximum observed total lengths (LT) for both species and sexes. A large proportion of mature females were neither pre-ovulatory nor pregnant, and the reproductive cycle included a distinct resting phase after pregnancy. For D. calcea, mean ovarian fecundity was 12 and maximum observed litter size was 10 (average of six); D. quadrispinosa averaged 17 pups per litter. Birth LT was 28–33 cm for D. calcea and 23–25 cm for D. quadrispinosa. The male and female reproductive cycles were aseasonal, and consequently, the length of the reproductive cycle could not be determined. Preliminary ageing data from dorsal-spine growth bands suggested that female D. calcea lived to 31–36 years and males to 24–32 years. The LT-at-age data using external bands on the spines showed maturity occurring at 15·5 years (males) and 21·5 years (females), whereas banding on the internal dentine indicated maturity at 10·5 and 17·5 years for males and females. Thus, a female lifetime of 31–36 years allowed for a maximum of 7 litters if a 2 year cycle is assumed or only five litters with a 3 year cycle, resulting in a lifetime fecundity of only 42 pups (2 year cycle) or even lower (3 year cycle).

Abstract: The content of liver oil from deep-sea sharks caught in Canary waters was examined to ascertain whether the species studied might be a source of commercially valuable squalene. Sixty-three sharks caught at depths of 600–2100 m represented seven species: Centroscymnus coelolepis, Centroscymnus cryptacanthus, Centrophorus squamosus, Centrophorus lusitanicus, Deania histricosa, Deania profundorum and Etmopterus princeps. The relative weight of the liver ranged from 15% to 26% of total body weight and 59–82% of the liver wet weight was oil. The major lipid classes were hydrocarbons (45–77% in liver oil), as is typical of most deep-water sharks. High concentrations of squalene in the livers (27–61% of liver wet weight) suggested that sharks caught in deep waters off the Canary Islands could be a rich source of squalene. Resumen. Se ha examinado el contenido de aceite en higado de tiburones capturados en aguas profundas de Canarias, con el fin de comprobar si las especies estudiadas pueden constituir una fuente valiosa de escualeno a nivel comercial. Para ello fueron analizados 63 ejemplares de siete especies de tiburon capturadas a una profundidad entre 600 y 2100 m: Centroscymnus coelolepis, Centroscymnus cryptacanthus, Centrophorus squamosus, Centrophorus lusitanicus, Deania histricosa, Deania profundorum y Etmopterus princeps. El peso de los higados supone el 15–26% del peso total de tiburon y el 59–82% del peso de higado es aceite. Los lipidos que se encuentran en mayor proporcion (45–77% en aceite) fueron identificados como hidrocarburos, lo cual es tipico en la mayoria de los tiburones de profundidad. Los higados contienen altas concentraciones de escualeno (27–61% en peso de higado) indicando que efectivamente los tiburones capturados en aguas profundas de Canarias pueden ser una buena fuente de escualeno.