44 



D. 6—5—04. Wliilst we had had bnt small takes of animal plankton in the Skager 

 Rak, northern and eastern Kattegat and Great Belt, such a large quantlty of young Aurelia, in 

 size from a farthing to a half penny, ns also Sarsia appeared to day in the western Baltie, that 

 each haul with the young-fish trawl in intermediate lavers gave several liters. Many Sagitta and 

 PleHvobravhia were al.so pi-esent. W'e got the impression that these forms, which are carried out 

 and in the Belts by the currents, are here collected together. It is also possible, that when they 

 are brought from the Great and Little Belt into the 10—20 fathoms deep basin west and south 

 from Ærø, they sink down into the deeper, salt lavers, which are almost stationary (see p. — ), 

 and the eiirface-current which is not sufficiently salt to support them, passes over them. 



As witli the Jelly-flshes, so with the jish-cggs. JSIany eggs were taken to-day, and they 

 are accustomed to remain here iintil the young appear. as they are at liberty to hatch out with- 

 out being carried away as in the Belts. Thus we also found many fish yoimg to-day, amongst 

 others the plaice young. As examples may be given: 



W. of Skjoldnæs, 18 fm Young-fish trawl — 3 fm., 10 minutes: 14 iMce young, from 

 (5 mm. (with yolk-.sac) to 9 mm., as also many other fish young. Young fish trawl — 16 fm., 

 20 minutes; 11 plaice young, all symmetricai, as also many other fish young. 



The whole of the jielagic life was further liack in developraent than wliat we had found 

 to be the case in the northern Kattegat. In the latter region the Aurelia young were throughout 

 larger, and we found no plaice eggs, whilst here we took several*, certainly with advanced 

 embryos. In the western Baltic all the plaice young were syiumetrical, some even with yolk-sac. 



In 8øby Bay we searclied both with the "bobinet" net wading and the "halt'-moon" net 

 towed after the boat in a little deeper water. The bottom here was of fine sand, but no plaice 

 were taken, either of the O or Igroup. 



There is thus a great difference in the plaice yoitng we met with at the 

 end of April in our northern waters and those we found iu the beginning of May 

 in the western Baltic. On the coasts of the North Sea and Kattegat metamorphosed 

 young were already found before the end of April; we found none in the western 

 Baltic even on the 6th of May. Both in the Sljager Rak ou April 28th and in 

 the western Baltic on May 6th we found many pelagic plaice young; but it was 

 ouly in the Skager Rak that some of them were asymmetricai, whereas the eggs 

 of the plaice were only found in the western Baltic. 



The plaice young in the beginning of May are thus much further hade in 

 development in the western Baltic than in the northern Danish -waters. 



On May 17th 1904 we were again stationed to the west of Skjoldnæs, 

 18 fm (see Tab. 1, western Baltic). On this day I have noted in the journal. 



D. 17 — 5 — 04. INIany pelagic plaice young were found here at Ærø on May Gth. The 

 question is now, whether those have begun their metamorphosis and have approached the coast. 



As before, we made some intermediate hanls with the young fish traA\'l to the west of 

 Skjoldnæs, and we again got some plaice yoimg, all of which were small, l)ut little larger than 

 those taken on the 6th, and they were all symmetricai. 



A vertical haul with the pelagic net gave, as mentioned earlier, 88 eggs, amongst which 

 one plaice egg. 



In Søby Bay we sought without result for the plaice young on the sands at the coast, 

 in ca. I fool and also a little deeper water to 1'/. fm. 



The plaice young are thus not much further on in development than on May Gth. In 

 other regards also the pelagic life recalls that of 6th. Sarsia and Aurelia were to-day again 

 extremely numerous in intermediate water-layers, the specimcns of the latter were somewhat larger 

 than before. 



The hydrographical conditions were almost as on IMay Gth. 



* (lur finding of the plaice eggs in the western Baltic on the (ith of May is mentioned 

 above p. 41. 



