12 



to be soiight for at deeper layers than in the western part, but it holds good for 

 both regions, that water of at least 15 7oo salinity is found at the bottom at 

 sufficiently deep piaces. As mentioned, some fish eggs at any rate eau float at a 

 salinitj' of 14 "/oo; the conditious are present in both regions therefore for the 

 occurrence of pelagic eggs. In the true Baltic we need ouly expect to find them 

 near the bottom; iu the Western Baltic, on the other hånd, the surface-water is 

 often of sufficient salinity to be able to float some of the pelagic eggs. 



Our investigations in 1904 (see Tab. I) have also shown, that pelagic fish 

 eggs eau also be found at the surface in the true Baltic, but we have always 

 found by far the greatest number in the deeper layers, as can be seen from 

 Tab. I. Thus, whilst in the Great Belt, for example, we may distinguish between 

 an occurrence in the surface-Avater and therewith a northgoing tendeney and an 

 occurrence iu the bottom-water and therewith a southgoing tendeney, in the ivestern 

 Baltic the coudition is somewhat differeut. 



The latter region can be divided according tb depth into a ivestern and an 

 easiern part, separated by a line drawn from the south point of Langeland almost 

 in a S.S.W. direction (see course of the 10 fathom line on the Chart (p. 24). The 

 eastern part of the western Baltic forms the counection between the true Baltic and 

 Great Belt, and both the outgoing surface-current and the ingoing bottom-current 

 flow through it. The irestern part of the western Baltic lies outside of the main 

 line of the ourrent; the surface-water may perhaps be often renewed, but the 

 deeper layers lie hiddeu at the bottom of a deep basin of 10 — 20 fathoms, which 

 oomes into communication with the other waters only by means of a narrow 

 channel south from Langeland (see course of 10 fathom line on the Chart). This 

 basin contains almost stagnant water. It has thus been proved, both by the 

 German investigations (Ehrenbaum and Strodtmaun, 1. cit.) and our own (see Tab. I), 

 that iu the deep water between Als and Ærø great changes in the salinity occur 

 but rarely, and the temperature here rises very slowly in the course of the sum- 

 mer, a sign that the water-masses at the bottom of the western part of the western 

 Baltic are seldom renewed. As it is mainly in these water-masses that the pelagic 

 fish eggs are found, the eggs are therefore not carried aivay during development 

 as in the Belts and Kattegat; for this reason they are always taken in relatively 

 large numbers in a vertical haul with the pelagic net at the deeper parts of the 

 western portion of the western Baltic. 



This region is not the ouly part of tlie Danish waters remarkable for 

 retaining salt water-masses which are seldom removed. In "De danske Farvandes 

 Plankton, I' p. 249 the Diretor points out, that piaces occur in the Southern 

 Kattegat, where cold resting water-masses are found near the bottom, and be con- 

 .siders that these regions retain the pelagic eggs or at any rate retard their 

 removal. Similar localities are found in the north of the Litile Belt (between Funen 

 and Endelave), in the Sound (the deep gut north of Hveen) and other piaces. 

 These are always of importance in the Danish inuer waters, not only for the 

 occurrence of the eggs but also for the development of the eggs and young fish. 



If we consider the conditions in the true Baltic, we find there only a 

 further development of the couditions in the western part of the western Baltic. 

 In the inner parts of the true Baltic the upper water-layers cannot float the pelagic 



