東部ベーリング海トロール漁場における魚群の移動と底水温の変化

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The oceanographic investigations and fishing by one-boat medium trawling were carried out at about one hundred and fifty stations on the continental shelf of the eastern Bering Sea during the period from April to June, 1960. In this region, two distinct fronts of water are encountered: that of the relatively warm water above 3.5°C which creeps into the region along the sea bottom from the southwestern offshore region, and that of the cold water below 0°C which has been severely cooled beneath the ice of the sea during the preceeding winter over the northern portion of this region. During the spring from April to May, in the vicinity of the front of the relatively warm water a tremendous number of fish abound, especially yellow-fin sole, Limanda aspera which is the most dominant species in this region. In June, when the bottom temperature rises a little gradating the front of the cold water, the shoals of yellow-fin sole move northeastward into the cold water region detouring around the severely cold water below 0°C. In this season the shoals of yellow-fin sole disperse widely and the catches by fishing boat decrease rapidly. After this, they move to the west toward the deeper cold region during the rise of bottom temperature in the shallower coastal region. About that time, a large gradient of temperature begins to form approximately along the 50-meter contour of the bottom. This is due to the fact that the water shallower than 50 meters is well mixed from surface to bottom through the connection of the upper layer mixed by wind action and the lower layer disturbed by bottom friction increasing the bottom temperature, while the water deeper than that forms s thermocline between the upper and lower layers preventing the heat from being transported downward. The yellow-fin soles, at this time, again close up in shoals along this belt-like region of the large gradient of temperature, perhaps being retarded there, on the way of their westward migration. To examine the process of the change of the bottom temperature, the amount of heat received at the surface was calculated at two stations where the observations were made twice at an interval of about twelve days. The heat amount received at the surface approximately agrees with the increase of the heat content at the stations, showing that the rise of the bottom temperature is due to the surface heating and vertical conduction. In addition, the values of vertical eddy conductivity in the thermocline were calculated together with those at several stations where the change of the bottom temperature greatly influences the movement of the shoals of yellow-fin sole as mentioned above.
公益社団法人日本水産学会の論文

東部ベーリング海トロール漁場における魚群の移動と底水温の変化

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