Plankton of the Northwestern Part of the 



Kuroshio and the Waters of the Pacific 



Ocean Adjacent to the Kurile Islands* 



By 



K. A. Brodskii 



As a result of many years of work by 

 planktologists, we have an outline of the zoo- 

 geographical divisions of the Far Eastern seas 

 and the adjacent part of the Pacific Ocean, but 

 the most important area--the area of contact 

 of cold and warm waters in the northern part 

 of the Pacific Ocean--has remained weakly il- 

 luminated. At the same time this area (the 

 Pacific adjacent to the Kuriles and the Kuro- 

 shio) is of great interest, both theoretically and 

 practically. Here can be observed a sharp 

 change in conditions as a result of the rap- 

 prochement of the Kuroshio current and the 

 cold waters to which are given the general 

 name of "Oyashio". It might have been ex- 

 pected that through this very area would pass 

 the boundary of the zoogeographical provinces 

 and that there would occur here zones sharply 

 differentiated by the composition and quantity 

 of the plankton. Comnnercially the area is of 

 substantial interest as a fishing ground for 

 tuna, saury, and other valuable species. The 

 Kurile waters, as is well known, are also a 

 whaling area. 



The plankton of the Kuroshio and of the 

 part of the Pacific adjacent to the Kuriles has 

 hardly been studied at all. A few expeditions 

 have collected plankton at a small number of 

 stations. Of published works we can mention 

 only the papers of Wilson (194Z, 1950), who 

 worked on the collections of the Albatross 

 (1900) and the Carnegie (1929). Some Japanese 

 works concerned with the results of hydrologi- 

 cal investigations in this area contain inciden- 

 tal information on the plankton (for example, 

 the works of Uda), but they do not give any sort 

 of general presentation of the composition and 

 distribution of the plankton. 



Soviet expeditions, especially those of the 

 vessel Vitiaz', have made more or less 

 detailed investigations of the plankton of the 

 Kurile Islands and the region of the Kurile 

 Trench (Vinogradov 1955, Zenkevich 1955), but 

 the area of investigation of these and of some 



*From Trudy Instituta Okeanologii, 

 Academy of Sciences of the USSR, Vol. U 

 p. 124-133, 1955. 



other expeditions (on the whaler Shkval, 1951) 

 have been limited by 40°N. latitude and did not 

 extend to the frontal zone of the Kuroshio, much 

 less to the proper waters of this current in its 

 northwestern part. 



In 1953 the author of the present paper 

 (from the Zoological Institute of the USSR Acad- 

 emy of Science) took part in expeditions of the 

 Institute of Oceanology of the USSR Academy of 

 Science and of the Pacific Research Institute for 

 Fisheries and Oceanography (TINRO) and col- 

 lected plankton in the waters of the Pacific ad- 

 jacent to the Kuriles and in the northwestern 

 part of the Kuroshio. Our basic task was to 

 study the composition and horizontal distribution 

 of the plankton in the surface layers of the 

 water. The work attained the objectives of dis- 

 covering the northern boundary of the Kuroshio, 

 establishing the zonality of the distribution of 

 the plankton, and clarifying the composition of 

 the basic group of the zooplankton, the copepods. 



The basic sampling tool was a fish-egg net 

 of No. 15 bolting cloth with an opening 80 cm. 

 in diameter. The hauls were made at the 0-50 

 m. level. The selection of the basic net and 

 depth of hauls was determined by the following 

 considerations. The fish-egg net is good for 

 catching the adult stages of copepods and gives, 

 perhaps better than the Juday net, a picture of 

 the distribution of the larger forms of the cala- 

 nids, which is important for answering practi- 

 cal questions about the feeding grounds of fishes 

 and whales. The second consideration in favor 

 of using the fish-egg net and the 0-50 m. stra- 

 tum was the necessity of comparing the 1953 

 data with those obtained in the northwestern 

 Pacific by the whaler Shkval in 1951. 



The materials we had led us to assume that 

 we would find the greatest biomassof the plank- 

 ton in the 0-50 m. layer not only at night but 

 also in the daytime. This assumption was sup- 

 ported by special investigations carried out by 

 us in 1953. 



As supplementary collecting gear we used 

 a Juday net of No. 38 gauze for hauls at stand- 

 ard levels from 200 m. to the surface. 



The arrangement of the sections was 

 planned to take in the largest area possible with 

 the smallest expenditure of time and to cut 

 across the nnain streams of both cold and warm 

 currents. Therefore the sections were perpen- 

 dicular to the Kurile chain and extended from 

 400 to 750 miles in a south-southwest direction. 

 In all, six such (long) sections were made, 

 connected by shorter transverse ones. The 



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