ON THE CIRCULATION IN THE NORTH PACIFIC IN 

 RELATION TO PELAGIC FISHERIES 



By MiCHiTAKA Uda 



Tokyo University of Fisheries 

 Kurihama, Yokosuka City, Japan 



On the charts plotted by the author, the semi-permanent boundaries 

 of the water masses (fronts) in the Northwest Pacific adjacent to 

 Japan, i.e. the Coastal Fronts, Oyashio Front (Polar Front or Subarctic 

 Convergence), Kuroshio Front, Warm and Cold Fronts in the Japan 

 Sea, Subtropical Convergence, Equatorial Counter Front, Continental 

 Front are shown in relation to pelagic fisheries grounds of tuna, skip- 

 jack. Pacific saury and whales (Fig. 1). Briefly we can summarize the 

 following three types of pelagic fishing grounds on the above hydro- 

 logical point of view: 



(1) Those produced by the planktonic livings and fishes in the 

 compressed zone of the optimum water temperature due to mere con- 

 vergence (e.g. the skipjack fishing grounds in the northern boundary 

 zone of Kuroshio and the Pacific saury fishing grounds near the Oya- 

 shio Front). 



(2) Those produced by marine organisms due to the up welling 

 of the water of rich nutrients in the deeper layer obeying Nathansohn's 

 theory (e.g. the fishing giounds of sardine, squid, yellow-tail, bluefin 

 tima, mackerel, etc., or some varieties of this type), indicating dense 

 concentrations near the coastal front and the fishing grounds on the 

 eddies around the islands or capes (mackerel, flying fish, etc.) and 

 around banks (skipjack, tuna and mackerel, etc.). 



(3) The combined fishing grounds of (1) and (2) types (e.g. 

 the marginal convergence of the upwelling area at the front of the 

 cold water such as the fishing grounds of the albacore, whales, Pacific 

 saury, etc.). 



Further we will inspect the oceanographic structure in the North 

 Pacihc by means of the nucleus method. The depth of the inter- 

 mediate water S min. and the value of that depth during the period 

 1931-41 were plotted in Figures 2, 3 and 4. 



The intermediate water in the Northwest Pacific may be con 

 sidered as the carrier of the rich nutrients which are produced in the seas 

 of high latitudes and fertilizer resulting in the high production in the 

 seas ot lower latitudes. The prevalence of the cold water circulation, 



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