146 Treubia Vol. Ill, 2. 



The biological part of the work was, practically speaking, confined to 

 the Java Sea. 



The Eastern boundary of this very shallow transgression sea coincides 

 with that of the continental shelf. This boundary can approximately be 

 indicated by the 100 fathoms line. 



Over -/g of its area the Java Sea is less then 30 fathoms deep, while 

 depths of 50 fathoms practically never occur. 



The surface area of the Java Sea amounts to 450,000 square kilome- 

 tres approximately, the cubic capacity only to about 20,000 cubic kilometres. 



A large number of plankton samples were collected by me, both on 

 the periodical trips to get hydrographical data together, made in May, 

 August, and November 1Q15 and in February 1Q16, as well as during a 

 number of trips over the fishing grounds along the North coast of Java. 



The plankton samples were collected with the aid of two vertical closing 

 nets. The filtering surface of the largest 4 Metres long net, whose opening 

 has a diameter of 1.30 Metres, consists of No. 3 plankton gauze from the 

 Swiss Silk Bolting Cloth Manufacturing Company Ltd. Thai. The small net 

 1.50 Metres long, and whose opening is 0.50 Metre diameter, has a filtering 

 surface of No. 25 gauze from the same manufactory. 



An analysis of these plankton samples shewed, amongst other things, 

 that the production of organic matter by the phytoplankton is greatly 

 promoted in the Java Sea by the mixing of the sea water with the fresh 

 water supplied by the rivers of Sumatra, Borneo and Java. 



It is probable that this river water is the carrier of nutritive substances 

 which are very suitable for the production of phytoplankton. 



It appeared to me in every case where the influence of river water 

 discharged into the sea was expressed in the salinity figures, that large 

 quantities of phytoplankton were met with; sometimes this was the case 

 even quite far (up to 250 sea miles) out to sea. 



On account of the material collected, as well as from theoretical con- 

 siderations, I think that the Java Sea must be considered, in the first five 

 months of the year at any rate, a very productive region. 



In connection with the investigation of the plankton, I have examined 

 on the fishing grounds of Java, Madura and the Kangean Archipelago the 

 stomach contents of about 16 species of pelagic fishes which feed on 

 plankton 



These fishes were caught with the native pajangnet (a kind of seine net). 



The most important of these fishes are : — the lajang (Decapteriis kiirra 

 Blkr.), the deles (Decapteriis macrosoma Blkr.), the selar bentong (C<7ra/ZA: 

 cramenophthalmiis C. V), the selar tjomo (Caranx affinis K, v. H.), the 

 selar kuning {Caranx leptolepis K. v. H.), the kembung lelaki {Scomber 

 kanagiirta C, V.), and the lemuru or sambolah (Cliipea leiogaster BLKR.)- 



At the same time I have measured large numbers of these fishes to 

 gain an insight into the question of their growth and spawning season. 



