An investigatioii of young fishes must also embrace tlie hottom-stages. We 

 have thei'efore not restricted our investigations with tlie young-tish trawl to the 

 intermediate layers, but have also made uumerous hauls on the hottom with this 

 trawl, both on the bare ground in deep water and on the Zostera and algæ covered 

 grounds near the coast. The "young-fish trawl on blocks" has often been used 

 OU such ground for the capture of the young of the cod, especially wliere the 

 bottom was stouey. A table giving the results of these investigations, though uot 

 printed, has served as the basis for the summaries employed in the special portion 

 of this work to show the occurreuce of the bottora-stages of tiie cod (Tab. A, p. 24) 

 and also of tiiose of the plaice (Tab. G. p. 40). 



General Part. 



Hydrograpliy. 



During our work at sea on the investigations of the pelagic eggs and young 

 of fishes, we have taken data regarding the hjidrography of the place at each station. 

 Our special aim was to find the boundary between the salt, deeper layer and the less 

 salt, surface layer. Under normal conditions we have always been able to detect 

 such a boundary in the deeper parts of all the regions, from the true Baltic to the 

 Skager Rak, including the latter. The difference between the temperature and especially 

 the salinity at a little distance below and above the boundary is often vcry great. 



It was only when we knew the salinit}' at the surface aud bottom and the 

 boundary mentioned, that we could determine in what depths we wished to fish 

 with the pelagic net and young-fish trawl; aud if the hydrographical data at the 

 various stations, given in Tab. 1, is compared with the depth of the haul made 

 at the same place, it will be seen, that we have used our knowledge of the hj'dro- 

 graphical conditions for the fisheries work. I may mention one exemple: 



D, 27—5—04. S.O. f. Sprogø, 20 fm. (Tab. 1, Great Belt). 



O fm. — 10., "C. — 12.„ "/„„ salinity 



10 . — 10.,, . — 15., . 



15 . - 7., » - 29., . 



20 . — 7., . - 29.9 • 



We first of all determined the temperature and salinity at tlie surface and 

 bottom aud then at a depth of 10 fathoms. These three determinations showed 

 us, that we were still in the surface water at 10 fathoms. We therefore sank the 

 water sampler down to 15 fathoms and reached, as can be seen, the salt bottom 

 water. The upper boundary of this must therefore have been at a depth between 

 10 to 15 fathoms. 



We reckoned now that the pelagic eggs would be floatiug on the surface 

 of the bottom water. This was of sufficient salinity to support them, whereas tlie 

 great majority would sink down through the surface water, which even at 10 

 fathoms down, that is, near the boundary to the bottom water, was only 15.3 "/oo- 



