11 



Skager Bah; but from March to Juli/ thcy remained nboul the same level, in August 

 they decreased and ivere qidte inconsideraUe in September to December. 



The Great Helt resembled the Kattegat mostlij in regard to the occurrence of 

 the eggs, but the conditions ivere not so uniform. 



lu tbe Baltic only the surface layers were fished during the investigations 

 1898 — 1901 and eggs were foiind in but isolated cases. 



Vertical hauls with the pelagic net from the bottom to the surface give 

 good information concerning the density of the eggs at the place investigated, Ijut 

 show nothiug as to the depths at which the eggs are floating. This problem must 

 be solved in a difierent way. On pp. 250 — 254 of "De danske Farvandes Plank- 

 ton, II" the Director has discussed the point in great detail. 



In the "Biol. Stat. Beretn. XII" p. 15 — 18, the Director again refers to the 

 questiou and remai'ks, that a bouudary-line can be indieated at all times between 

 the parts of the Danish waters where eggs are found ou the surface and the parts 

 where they first occur in deeper layers. This bouudary was determined in March — 

 April 1902 (1. c. p. 17 — 18) by a series of surfacehauls with the pelagic net, and 

 at that time cut off the true Baltic, the eastern part of the Western Baltic as far 

 as the south point of Langelaud and also the Sound from the other Danish waters. 

 East and south of this boundarj' no fish eggs were takeu in the surface hauls 

 with the pelagic net. The same line, which limited the occurrence of fish eggs in 

 the surface-waters, also distinguished approximately the salinities on the surface 

 of above and below 14 7oo- 



The majority of the pelagic fish eggs float however in water-layers of 

 somewhat greater salinity, as appears partly from our Table I (p. 72) partly from 

 the summary of the occurrence of fish eggs at the surface aud bottom of the Great 

 Belt in 1899 in "De danske Farvandes Plankton I" p. 253. 



The position of the eggs in the water-masses has great importance for their 

 fate, since, as mentioned in the previous chapter, two opposing currents are usually 

 passing through the Danish waters, an outgoing surface-curreut and an ingoing 

 bottom- current. As soon as the surfacecurrent on its way from the true Baltic to 

 the North Sea attains a sufficient salinity to be able to support the pelagic eggs, 

 these float upwards into it and are carried away in the direction of the North 

 Sea; but imtil the surfacecurrent is salt enough to be able to support the eggs, 

 these remain in the bottom water and follow its movements. The conditions in 

 the latter cases are more complicated and more difficult to observe than when the 

 eggs are found in the surface-water. I shall therefore go a little more into detail 

 on the occurrence of the pelagic eggs in those parts of the Danish waters where 

 they are found in the liottom- water. 



In consequence of Strodtman's remarks on "Der indigene Fischbestand der 

 Ostsee" (Ehrenbaum und Strodtmann, 1. c. p. 121—126), we paid special attention 

 in 1904 to tlie conditions in the Baltic and took frequent observations there (see 

 Tab. 7). The hydrographic conditions in the Baltic are somewhat difterent from 

 those we find further uorth in Danish waters. Ehrenbaum and Strodtmann (1. c. 

 p. 69) give a graphic representation of the conditions as to salinity in the Baltic 

 in 1903. From this it appears that fairly salt water is found at the bottom both 

 in the true Baltic and in the western part. In the true Baltic the salt water has 



