256 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



we can give the following general scheme of movements of 

 plaice in Lancashire water. (1) There are practically no 

 regular migratory movements of plaice under about eight 

 inches in length. These fish live, for the most part, in the 

 shallow intra-territorial waters, particularly in the shal- 

 lower channels. They move about irregularly, the direction 

 and extent of the movements depending on the tidal 

 streams ; on slight temperature changes produced by tidal 

 streams ebbing off the land, or flowing in from the open sea, 

 or by freshets coming down from the rivers; and on the 

 individual " caprice " of the fish themselves. They do 

 not migrate " in search " of food, but moving about irregu- 

 larly they encounter accidentally food, such as beds of 

 young mussels or other shell-fish, and having " struck " 

 the food, they remain in its locality : a shoal of plaice thus 

 gradually forms. This is all that we can say about the 

 movements of plaice of the smaller range of sizes. Then 

 in the early spring and summer these fish begin to grow 

 with the increasing temperature of the water. But the 

 latter soon exceeds its mean, or perhaps late spring value 

 — a value which is probably the optimal one for these 

 fishes. A migration offshore, that is in such a direction 

 as to compensate for the rise of temperature inshore, now 

 begins, the fish endeavouring to enter water of lower 

 temperature. In this way the shoals of plaice which 

 form round Nelson Buoy, between here and Liverpool 

 Bar, or in the channels and off the banks out from the 

 Estuaries of the Dee and Mersey, are formed, and thus the 

 summer fisheries in these regions become established. 

 They continue until the temperature of the water falls 

 below the optimal value in the late autumn, and then the 

 shoals break up. The smaller fishes migrate inshore, pro- 

 bably there is a range of water pressure which their 

 habitats do not exceed. They hibernate to some extent 



