20 



good qnality aud size. In tlie Baltic Sea proper, between Moen and Riigen, 

 il few millions have beeu caught of late years, of a peculiarly small, Init iiume- 

 rous form, so small tliat its marketvalue is but very little. From these 

 j)arts eastwards the plaice evidently decreases very much in number; but 

 Schiemens has found it east of Gothluud at the eastmost of the stations 

 investigated, and it is found, although sparsely, as far up as Stockholm, 

 mostly, I presume, on the deep. The piaces within the Skaw where I have 

 caught most plaice in the shortest time, are the seas between Riigon, 

 Schoueu, and Møen. Their numerousness here can be compared only to 

 that of the young plaice (the II and Ill-group) at Thyboron in the western 

 part of the Limfjord or at Horns Rev near Esbjerg. At Møen, on the 

 otlier band, we catch, as I have said, almost exclusively grown-up fish. I 

 shall not here enter into the particulars as to the age, growth, and "races" 

 of the plaice; they will be given, most likely, in a later publication by one 

 of my co-workers. One thing only I shall mention: that a numerous and 

 widely distributed stock of grown-up fish is living east of Gedser (cmp. 

 table I, column III), and this though the Ogroup is so rare in these very 

 seas, that, in spite of all our searching, only c. 50 specimens that may be 

 assigned to this group, were takeu through many years together, against 

 thousands in our other seas. The following group (I) is also scaree (cmp. 

 table I, column III), though perhaps not equally scaree every year (See 

 "Report of the Bioi. Station, IV", table VII, column 10). 



We can imagine this large stock in the Baltic Sea to be renewed in 

 3 ways only: either 1) exceedingly dowly, by a very slight, annual pro- 

 pagation, or 2) by a large propagation in certain years, in which the 

 hydrographic conditious then must be very ditferent from the usual, and 

 the fry occur in large multitudes, or 3) by immigration. In the tirst 

 case the plaice must be very old in the Baltic Sea, of which their otoliths 

 perhaps might give us information. The researches have as yet never indi- 

 cated auythiug about a numerous fry in certain j^ears, and this possibility 

 is most probably excluded, already from a hydrographical point of view. 

 The only hypothesis remaiuing is then that of immigration, which Schiemens 

 as well as JEhrenhaum and Strodtnwnn seem inclined also to adopt. It must 

 then especially be the Igroup that immigrated from the Belt-Sea to the 

 western part of the Baltic. The bodily differences between the plaice in 

 these seas may very well agree with such a hypothesis. But this immigra- 

 tion must be elucidated by renewed investigations into the occurrence of 

 the fry, particularly in the southern jmrt of the Great Belt and along the 

 German shores of the western part of the Baltic Sea; for in this I fully 

 agree with Ehrenhaum that tlie fry must come either from the Belt-Sea or 

 from the western part of the Baltic, scarcely from the Cattegat properly so 

 called. 



