Overfishing of Three Siganid Species (Family: Siganidae) in Lagonoy Gulf, Philippines
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概要
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Juvenile and older Siganus canaliculatus, S. spinus and S. argenteus were assessed in Lagonoy Gulf from analysis of total juvenile catch trend obtained in commercial fishing operations and using length-basedfishery methods to generate evidences of overfishing of the resource. Estimates of annual instantaneous total, fishing and natural mortalities were high which corresponded to their high exploitation. Exploitation rates of the three species were higher by 34-64% beyond the level that would be sustainable. Capture lengths were generally lower than their reported maturity size which means the fishes were caught before they would have contributed to recruitment in the fishery. Total juvenile catches and catch-per-unit-effortin 2001-2004 were continuously declining, which registered 50% decline in 2003-2004. The highest volumes of juvenile catch were obtained consistently in April and May new moons although the appearance of juveniles is apparently year-round. At about the same period in summer (April and May), the larger, gravid siganids, were fished intensively although the fishery has been practiced throughout the year. The high exploitation of juveniles and larger siganids in the gulf could not be expected to decrease in coming years but rather it would intensify given the historical uptrend of fishery exploitation in the gulf If leftunregulated within sustainable level for the older fish and not rationalized until completely stopped for the juveniles, this will lead to significant stock depletion that will be disadvantageous to the fishery as a whole.
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