distance between stations was 40 miles; 

 besides the collection of plankton, at each sta- 

 tion the water temperature was taken at levels 

 down to 200 m. For studying the seasonal dy- 

 namics of the distribution and composition of 

 the plankton the sections were run twice: from 

 July 9 to August 12, and irom September 7 to 

 23. 



The plankton collections were made from 

 a medium fishing trawler (SRT 662), on the 

 deck of which was installed a winch of the 

 "Ocean" type with an electric motor, foot- 

 brake, meter, and automatic level-wind. The 

 hauls were made with a galvanized steel cable 

 3. 1 mm. in diameter. 



encountered there, is extremely heterogeneous; 

 the warm-water plankton is especially rich in 

 groups and species. Most abundantly repre- 

 sented in it are the copepods, of which not only 

 are the calanoids numerous (more than 100 

 species) but also the cyclopoids, among which 

 abound extraordinarily beautiful, transparent 

 Copilia, Corycaeus, and Sapphirina . 

 Cladocerans are represented abundantly in a 

 small number of species. There are many 

 species of siphonophores, salps, pteropod 

 moUusks, hyper iids, radiolarians (mostly of 

 the family Acanthometridae), chaetognath 

 worms, and crustacean larvae, among them 

 the leaf-like Phyllosoma, the elongated Lucifer , 

 and others. 



The collection of plankton from a medium 

 fishing trawler, i.e. a relatively small (dis- 

 placement about 300 tons, with a 280 H. P. en- 

 gine) and extremely unstable vessel, which 

 rolls heavily in even a small sea, has some 

 special features. Under such conditions the 

 plankton net, in the water, at times experiences 

 very heavy dynamic loads even in a moderate 

 swell. This can easily lead to breaking of the 

 cable or damaging of the net. The net and the 

 cable are subjected to especially heavy loads 

 on the open sea with a constant monsoon of a 

 force of 5-6, which makes for the appearance 

 of large wind swells. In working on small 

 vessels it is essential to use an accumulator. 

 The "Ocean" type winch, with a 3. 5 KW elec- 

 tric motor, in itself appeared to be an excell- 

 ent accumulator. When there were heavy jerks 

 while the net was being hauled up, the motor 

 would cease to pull the net, and the cable would 

 even pay out slightly. Thanks to this, not a 

 single net was lost or torn during the whole 

 operation. 



In all, 139 stations were occupied fronn 

 July 9 to September 23, 1953, 470 plankton 

 samples were taken, and 653 water tempera- 

 ture determinations were made. A total of 

 more than 10,500 miles was run, most of it on 

 the open ocean. The investigations took in a 

 significant area of the northwestern Pacific 

 Ocean, from the Kurile chain south to 34°N. 

 latitude. The southwestern boundary of the 

 area runs approximately along the meridian of 

 the northern tip of the island of Sliikotan, and 

 the northeastern one along the meridian of Cape 

 Lopatka in Kamchatka. 



Results of the Analysis of the Plankton 



Com position of the Plankton. The systematic 

 composition of the plankton of the area investi- 

 gated, in view of the variety of the conditions 



Comparing the overall catalogue of cope- 

 pods, hyperiids, radiolarians, and other groups 

 from the area investigated in 1953 with the 

 species catalogued for the Japan Sea (excluding 

 its southwestern part) and the Bering and 

 Okhotsk seas, it is possible to convince oneself 

 that in species composition the plankton of the 

 area investigated by us is considerably richer 

 than that of all three of these seas taken 

 together. This refers especially to the surface 

 layers of the water. 



The zoogeographical composition of the 

 plankton is also varied, but there predominate, 

 particularly among the copepods and 

 cladocerans, tliree basic groups, which are ex- 

 tremely unequal in terms of the number of 

 species, as follows: 



1) Species of the North Pacific Temperate 

 Region--the connmon species of the Far Eastern 

 seas (Calanus tonsus, Eucalanus bungii, 

 Metridia pacifica, and others). This is the 

 poorest group in terms of species; 



2) Subtropical species of the Indo-Pacific 

 Subregion of the Tropical Circumequatorial 

 Region. This group is relatively richer in 

 species and includes many species of copepods 

 (genera Labidocera, Acartia, Paracalanus, and 

 others) and cladocerans; 



3) Tropical species of the same region and 

 subregion. This is the group that is richest in 

 species (of tlie genera Eucalanus, Nannocalanus , 

 Canthocalanus , Ncocalanus, Undinula, Candacia, 

 Paracalanus, Acrocalanus, Mecyanocera, and 

 others). 



The distribution of some of thi- species of 

 the second group is linnited to thi' waters adja- 

 cent to the Pacific coast of Japan. Tlu'se 

 species are related to the Japanese Subtropical 



17 



