Special care will be paid to the problem of the river mouths, where 

 very peculiar biological conditions are found and where a special estuarine 

 fish fauna exists which is typical for South-east Asia. A similar fish 

 fauna, though composed of different species, is found in the estuaries of 

 South New Guinea. 



Since the last congress in 1939 the following research was carried on in 

 the Java Sea by the Laboratory for Investigation of the Sea at Batavia : — 



1. A Hydrographic Survey of the Java Sea and Adjacent Straits 



• Four regular cruises, taking samples from the surface to the bottom, 

 were made — viz., in the months of January, April, July, and October 

 every year. Besides this work regular sampling was done at the surface 

 by shipping lines and lighthouses. The total amount of water samples 

 collected totalled up to about ten thousand a year. ■ Only salinities and 

 temperatures were determined. 



In general it can be said that the current-system changes twice a 

 year under the influence of the monsoons, which are the predominating 

 winds here, the long axis of the almost rectangular Java Sea lying parallel 

 to the direction of the monsoons. During the east monsoon water flows 

 into the Java Sea from the Flores Sea and the Straits of Macassar and 

 leaves it again through the Straits of Sunda into the Indian Ocean and 

 through the channels betw^een Sumatra and Borneo into the South China 

 Sea. In the west monsoon the direction of the currents are just the 

 reverse, whereas the general salinity is one to two promiUe lower than 

 in the east monsoon. 



This changing currents system, together with the varying salinities, 

 have a strong influence on the fisheries for Decapterus. 



Now and then oceanic w^ater through the Straits of Sunda is pouring 

 into the Java Sea in contrast with the general current system of the 

 east monsoon. This upsets this system for the south-western part of the 

 Java Sea and in accordance with this the general ordinary pattern of 

 the fisheries. 



No publications were ready at the outbreak of the war. 



2. A Survey of the Bottom Fauna 



This was done especially in the Bay of Batavia. Some interesting 

 facts were discovered. The bulk of the bottom species consisted of 

 molluscs.^ All specimens were very smaU, a sheU of 1 centimetre was a 

 large one. This bottom fauna proved to be totally different from the 

 molluscan fauna generally found on the shore, which therefore must live 

 in a very limited zone. 



The number of species, as always in the tropics is large. One station 

 produced 190 species (not individuals !) per square metre. The amount 

 of living matter, however, which can serve as fish food for bottom 

 dwellers was very low, a fact which is not encouraging for the development 

 of a trawl fisheries in a European style. 



In accordance with this the number of flat fishes (not the number of 

 species) is smaller than f.i. in the North Sea and the individuals are small, 

 too, 10-15 cm. being the average, some species and some localities 

 excepted. 



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