314 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



graphic investigations carried out in the Irish Sea is 

 that the plaice fishery in Red Wharf Bay and the 

 adjacent grounds is the result of an extensive immigra- 

 tion of fish into this area from somewhere else. The 

 rapid falling-off in the productivity of the fishery during 

 the latter weeks of the year must also be due to the 

 emigration of plaice from out of the North Welsh fishing 

 grounds into some other area — that is, unless it is the 

 case that the vessels simply cease to fish for some other 

 reason than the scarcity of plaice. If the fishery ceased 

 because the grounds were becoming depleted by the 

 intense fishing of the few last weeks of the year, the 

 curve of catches would fall more slowly than it does. 

 It also appears to be really the case that the plaice have 

 actually disappeared from out of Red Wharf Bay by the 

 beginning of the year, for the trawling experiments 

 made by the "James Fletcher" — such as they are: 

 there is a regrettable lack of these during January and 

 February — show that fish are then very scarce. It must 

 therefore be concluded that the fish do actually migrate 

 out from the Bay. The marking experiments support 

 both of these assumptions : it is the case that relatively 

 large numbers of marked plaice migrate into this area 

 from the fishing grounds further north and east, 

 it is also the case that a fair proportion of plaice marked 

 in Red Wharf Bay during the progress of the winter 

 fishery have been recaptured in other fishing grounds, 

 principally in Cardigan Bay and off the South-West coast 

 of Ireland, though some hare also been taken on the 

 Bahama Bank grounds. 



If the aperiodic fluctuations in the values of the 

 mean catches made are due to differences in the 

 quantities of plaice migrating into or emigrating out 

 from this area, or if these migrations are adaptations 



