Population Structure and Mortality of the Neptune Whelk <i>Neptunea arthritica</i> in Usu Bay, Southern Hokkaido

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  • Population Structure and Mortality of the Neptune Whelk Neptunea arthritica in Usu Bay,Southern Hokkaido
  • Population Structure and Mortality of t

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Abstract

Population structure and mortality rates of the neptune whelk Neptunea arthritica in Usu Bay, Hokkaido were estimated on the basis of seasonal changes in their age group densities. Mortality in hatchlings (0 year old) occurred gradually fromsoon after hatching through spring, with a mortality rate of about 60% during this period. Mortality rates of immature individuals (1 and 2 years old) were very low. Deaths of adults (older than 3 years old) occurred in June and July, with an estimated 76.3% of the adult population dying during this period in 1980. The age structure of the population showed the III age group occurred in the highest frequency, followed by the II age group. The 0 and _??_V age groups occurred in the lowest frequencies.The number of egg capsules per egg mass annually diminished withsubstantial reductions of the number of adults.The factors affecting mortalityand the decrease of resources were discussed.

Journal

  • Fisheries science

    Fisheries science 62 (2), 184-188, 1996

    The Japanese Society of Fisheries Science

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