Spatial and temporal distribution of Pacific cod Gadus macrocephalus juveniles in Mutsu Bay, Japan
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概要
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The spatial distributions of Pacific cod (Gadus macrocephalus) juveniles and their food organisms were examined in Mutsu Bay from April to July during 1988-1997. In April, large larvae (≤25 mm in total length (TL)) and pelagic juveniles (>25 mm TL) were widely distributed in the bay, and were concentrated at the same depths as calanoid copepodites during daylight hours. Geographical changes in cod TLs might have been due to transport by the Tsugaru Warm Current. After mid- and late May, juveniles and calanoid copepodites occurred on the bottom. Mean densities of cod juveniles fluctuated annually in April and June, and high densities occurred when calanoid copepods were abundant. Juveniles were rarely found at temperatures >12℃, and it is likely that they migrate out of the bay after late June when temperatures increase and the abundance of prey decrease in the bay. Pacific cod use Mutsu Bay as a nursery ground, and calanoid copepodites sustain cod larvae and juveniles as their prey until mid-June. Large fluctuation in mortality of Pacific cod might occur in pelagic juvenile and subsequent stages after April in Mutsu Bay.1988-1997年4-7月に，陸奥湾においてマダラ稚魚とその餌生物の時空間分布を調べた．4月には大型仔魚（全長25mm以下）と浮遊稚魚（>25mm）は湾内に広く分布し，昼間はカラヌス目かいあし頬の高密度分布層に集中した．仔稚魚の体サイズの地理的変異は，津軽暖流水による輸送により生じたものと推定された．5月中下旬以降稚魚とカラヌス目は海底直上に出現した．4月と6月の稚魚の平均個体数密度は年によって大きく変動し，稚魚高い個体数密度はカラヌス目の高い豊度とともにみられた．湾内の水温上昇と餌豊度が低下する6月下旬以降，稚魚は水温12℃を超える水域にほとんど出現せず，湾外に移動すると考えられた．マダラは陸奥湾を生育場として利用し，カラヌス目コペポダイトは6月中旬まで仔稚魚の餌生物として生残を支える．陸奥湾におけるマダラ仔稚魚の死亡率の変動は，主に4月の浮遊稚魚期以降に生じたものと思われる．
著者
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Takatsu T
Hokkaido Univ. Hokkaido
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Kooka K
Hokkaido Univ. Hokkaido Jpn
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Takatsu T
Graduate School Of Fisheries Sciences Hokkaido University
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Takatsu Tetsuya
Hokkaido Univ. Hokkaido Jpn
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