220 SALT-WATER FISHES 



Cole alludes to a remarkable condition of the Baltic, which, 

 arising out of the normally low and periodically lower specific 

 gravity of that sea, explains the long-discussed absence from 

 that sea of the very young plaice under 2 or 3 in. in length. 

 About once a month, according to Hensen, the Baltic is 

 of such low specific gravity that the plaice eggs sink ; 

 and the inference is that their development is thereby per- 

 manently checked, since floating eggs are not adapted to 

 healthy development at the bottom of the sea. The extra- 

 ordinarily low percentage of salt in that sea can hardly be 

 appreciated by those who have neither bathed nor fished in 

 it ; but the writer well remembers, though twelve years have 

 elapsed since he resided on its shores, the comparative difficulty 

 of keeping afloat on its surface for one accustomed to sea- 

 bathins in the Channel and Mediterranean, and also the 

 curious sensation of catching, a mile or two from shore, 

 such a medley of sea- and river-fish as plaice, pike, perch, 

 and cod, not necessarily on the same ground, but within an 

 area of probably less than an acre. The low percentage of 

 salt is not difficult to account for in a sea that, having no 

 outlet save the narrow strait that connects it with the North 

 Sea, receives so many torrential waters from the melting 

 snows of southern Scandinavia, besides so many slower yet 

 broader streams from the lowlands of northern Russia and 

 Germany. The curious variations in the salinity, however, 

 have yet to be satisfictorily understood. 



According to Cole and other observers, the young plaice 

 follow a very general rule of inshore migration, seeking the 

 shallows in the warmer months and the deeper banks in cold 

 weather. The writer named also quotes a remarkable case 

 of irregular migration on the part of large plaice, which was 

 brought to his notice by Mr. R. L. Ascroft. A heavy storm, 

 in 1885, washed the "sand-pipes" {Tectinarid) off the deep- 

 water banks into a channel of the Ribble estuary, and there, 

 for about four days, the sailing trawlers caught as many as 



