218 BRITISH FISHERIES 



catch of anchovies in the Scheldt ; and Hjort and 

 Pettersson, both investigators of the first rank, 

 have stated the probable relationship between the 

 herring fisheries and hydrographical changes in 

 the North Sea. The autumn herring fishery on 

 the east coast of Norway is due, according to Hjort, 

 to a " feeding migration," and is determined by 

 the movements of the Bank water of the North 

 Sea. The arrival of the herring shoals coincided 

 in time with that of water of a relatively high 

 temperature and of a salinity of 32-34. 1 Pettersson 

 also 2 ascribed the appearance of the herring shoals 

 in the Cattegat in autumn and winter to the move- 

 ments of Norwegian and Danish Bank water. No 

 one has yet contended that minute differences in 

 salinity and temperature as such affect the move- 

 ments of the herring. But this fish is a plankton 

 feeder, and such organisms as copepods and diatoms 

 are, no doubt, affected by these changes. And 

 since every fish is, in the long run, a plankton 

 feeder, we can recognise no essential distinction 

 between pelagic fishes, such as the herring, and 

 bottom-living forms like the plaice. 



Two other main charges have been made against 

 the methods of the international observations. 

 One of these appears to me to be founded on 

 some misapprehension of the precise methods 



1 J. Hjort, Hydrographic-Biological Studies of the Norwegian 

 Fisheries, Christiania, 1896. 



2 See papers in Scottish Geograph. fourn., 1894. 



