SCIENCE AND THE SEA FISHERIES 243 



Bay, one with a mean length of 23 in., the other with a mean length 

 of 29 in. 



The former fish have been reared in the Lancashire " nurseries." 

 The larger fish are those which have survived the intense summer 

 fishery of the Liverpool and Morecambe Bay areas. All these 

 plaice migrate into Redwharf Bay, when the sea temperature of 

 the Lancashire waters falls below a certain point . The fishery in 

 this bay terminates suddenly, before the stock of fish is exhausted, 

 the fish moving round the coast of Anglesea to Carnarvon and 

 Cardigan Bays, and even further south. 



The larger plaice caught in Cardigan Bay in the first few months 

 of the year have come from Redwharf Bay, and earlier still from 

 Lancashire waters. The migration into Redwharf Bay is not for 

 spawning purposes, since the fish spawn further south in deeper 

 water, it follows that a large proportion of Lancashire plaice are 

 spawned in Cardigan Bay and St. George's Channel, the larvae 

 being transported northwards by the Gulf Stream drift. Plaice 

 marked and liberated in Cardigan and Carnarvon Bays move 

 either towards the east coast of Ireland or the Bristol Channel. 

 There is no record of a plaice liberated in the Welsh Bays moving 

 up to the Bahama Bank area. Probably many of the migrations 

 made by the Irish Sea plaice are simply attempts on the part of 

 the fish to move about, so as to live under conditions as nearly 

 uniform as possible. 



Since all the plaice were measured before liberation and after 

 recapture, an indication of the rate of growth has been obtained. 

 A striking result is that the rate of growth in the winter is nil. 

 From October to March there is practically no growth ; it only 

 commences in April and becomes most marked in June, July and 

 August. The average annual increase in length is almost exactly 

 3 in., but this statement only applies to fish which were at the time 

 of marking between 8 and 10 in. in length. The cessation of growth 

 in the winter months cannot be connected with the spawning habit, 

 since the majority of the fish marked were not spawners. It is more 

 likely due to a great scarcity of food in the winter, and to a decrease 

 of metabolism. The weight of a plaice of given length is always less 

 in winter than in summer. Fish recaptured after two years had 

 grown from 6| to yl in. These fish after carrying the labels for 

 two years were evidently none the worse, being plump and in good 

 condition. 



