Tanaka S.,Tokai University |
Kitamura T.,Japan NUS Co. |
Mochizuki T.,Ibaraki Prefectural Oarai Aquarium |
Kofuji K.,Ibaraki Prefectural Oarai Aquarium
Marine and Freshwater Research | Year: 2011
The white shark, a top predator inhabiting the world's oceans, is an endangered species. However, knowledge of its life-history traits and population structure is still limited. We hypothesised that life-history traits would vary among populations because the species' various habitats are diverse and change through time. Age was estimated by counting growth bands in the centra of white sharks caught in Japan. The von Bertalanffy growth parameters were estimated at L∞=455cm TL, k=0.196 year-1 and t0=1.92 years for males and L∞=607cm TL, k=0.159 year-1 and t0=-1.80 years for females. The growth rate to maturity was higher than that known for individuals from California and South Africa. Male sharks matured at 310cm TL at 4 years of age and females began to mature at ∼450cm TL and 7 years. The D-loop-region sequences of mitochondrial DNA extracted from Japanese white sharks and GenBank datasets from sharks of California, Australia, New Zealand and South Africa indicate that Japanese white sharks form a monophyletic clade separate from the populations of other regions. The results suggest that unique life-history traits of Japanese white sharks may be caused by genetic differences. © CSIRO 2011.
Goto T.,Iwate Fisheries Technology Center |
Shiba Y.,Ibaraki Prefectural Oarai Aquarium |
Shibagaki K.,Ibaraki Prefectural Oarai Aquarium |
Nakaya K.,Hokkaido University
Zoological Science | Year: 2013
We examined gill morphology and ventilatory function in the carpet shark family Parascylliidae using 14 preserved specimens of Parascyllium ferrugineum, P. variolatum, P. collare and Cirrhoscyllium japonicum, and two live specimens of P. ferrugineum and P. variolatum. Morphological examinations revealed eight morphological characteristics related to the fifth gill, based on comparisons with other elasmobranchs, viz. large fifth gill slit without gill filaments, anatomical modifications in the fourth ceratobranchial cartilage and coraco-branchialis muscle, and the hypaxialis muscle associated with the fifth gill arch. Ventilation examinations using dyed seawater and prey items showed different water flows through the gill slits for respiration and prey-capture actions. For respiration, water sucked into the mouth was expelled equally through the first to fourth gill slits via a "double-pump" action, there being no involvement of the fifth gill slit. In prey-capture, however, water sucked into the mouth was discharged only via the widely opened fifth gill slit. This form of water flow is similar to that in other benthic suction-feeding sharks (e.g., Chiloscyllium plagiosum), except for the active water discharge by wide expansion and contraction of the fifth parabranchial cavity. The latter is dependent upon the morphological modifications of the fourth and fifth gill arches, derived phylogenetically as a mechanistic suction specialization in Parascylliidae. © 2013 Zoological Society of Japan.