— XIX — HOEK— INTRODUCTORY 



distribution of young plaice, and from the German side, a first report was published 

 in December 1903 1, a second in December 1904^, whilst a notice published at the 

 same time on the occurrence of young plaice in Neustädter Bay may be regarded 

 as a thirds. In Appendix G of this General Report, Dr. Petersen, the Convener 

 of Committee C 2, which is specially concerned with the plaice in the Baltic, pays 

 attention to the occurrence of the plaice in these waters. The chart (Tab. IX) which 

 he gives with this Appendix, indicates in the Baltic the boundary-lines to the east 

 of the pelagic eggs, the pelagic young fish, the bottom-stages of the young and 

 the adult fish of the plaice. 



Meantime, Dr. Petersen has published an extensive paper in the XII''' Report 

 of the Danish Biological Station, in which he describes, where and under what 

 conditions plaice-eggs may develop to young fish in the waters within the Skaw4. 

 This paper is based on the international material available up to that time and 

 was prepared as an explanation of these matters. It also concerns the problems 

 taken in hand by Committee C2 for the Baltic. From his investigations, Dr. 

 Petersen comes to the conclusion, that the eggs of the plaice which are met with 

 from the Skaw as far in the Baltic as Bornholm, can as a rule pass through all 

 the pelagic stages to the bottom-stages only where the water renders it possible 

 for them to reach the coasts at certain periods. The j^oung can then come on to 

 the low, clear beach lighted and warmed by the sim, which seems necessary for 

 their development, whilst those which are obliged to remain in the cold, dark 

 and deep water-layers of the Baltic obviously die as a rule. 



In the eastern part of the Baltic, as in the Gulfs of Bothnia and Finland, the 

 investigations have been specially concerned with the salmon and eel. These 

 investigations belong to the program of Committee C i, whose Convener is 

 Dr. F. Trybom. They have begun with the marking and liberation of specimens of 

 the species named. These investigations are making good progress though no 

 reports are as yet to hand. 



The purely biological investigations may be but briefly mentioned here. The investigauons 

 better means at present at the disposal of the investigations naturally lend them- °" '^'„V^^^l""" 

 selves at the same time, exceedingly well to the investigation of various questions 

 important in biological regard, though these questions are onl}- indirectly connected 

 with the main problems taken in hand. As examples of these biological investiga- . Bi°i°g'"' 

 tions. Prof. K. Brandt's work on the cycle of physiological changes ui the sea 

 and the importance of nitrogen compounds for the production in the sea, may be 

 mentioned. This is a continuation of several investigations carried out b)' V. Hensen 



I Krüger, A., Ueber die Verbreitung junger Schollen an der deutschen Ostseeküste im Sommer 

 und Herbst, 1903. Mitt. d. D. Seefischerei-Vereins. 1903. 



' Reibisch, J., Weitere Untersuchungen über die Verbreitung junger Schollen an der deutschen 

 Ostseeküste im Sommer 1904. MitL d. D. Seefisherei- Vereins. 1903. 



3 Duncker, G. , Junge Goldbutt { Pleitronectes platcssa, Z,; in der Neustädter Bucht. Mitt. d. D. See- 

 fischerei-Vereins. 1904. 



4 Petersen, C. G. Joh. , Hvor og under hvilke Forhold kunne Rodspsettens .^g udvikle sig til 

 Unger indenfor Skageu? Beretniug fra den danske biologiske Station. Xll, 1902 og 1903. Kjoben- 

 havn, 1904. 



investigations 



