SEA- FISHERIES LABORATORY. 115 



Sea-Perch ( L abr ax lupus) and Mackerel. 



So also with these fishes. They come into the Irish Sea 

 at variable times, but generally about May or June, and they 

 stay till about August and September. They also come up 

 from the South and retreat back there again. Hake, sea-perch, 

 and mackerel we may regard as southern fishes, and take their 

 northern limit of distribution to be some particular isotherm in 

 the sea. This isotherm, whatever it may be, changes from 

 South to North as the summer advances and then changes 

 back to the South as the sea temperature begins to fall, rather 

 rapidly in September and October. 



Herring. 



This is a well-known migratory species, but the conditions 

 that rule the movements of the fish are very complex and are 

 not clearly known as yet. There are two main herring fisheries 

 in the Irish Sea area : (1) the Welsh winter, and (2) the Manx 

 summer fisheries. The Welsh winter herrings appear in 

 Cardigan Bay in October and the shoals gradually move to the 

 North as the season advances, disappearing off the North Coast 

 of Anglesey sometime in January. The fish are mature ones 

 and are " full " when they first come on the coasts ; later on 

 they spawn, and by the end of the season they are usually in 

 the spent condition. 



The Manx herrings are sometimes found off the coasts of 

 the Island as early as February, but not in abundance. About 

 May they begin to become abundant and are to be caught on 

 the west, south , and east of Isle of Man. In July to September 

 they spawn, and soon after that the shoals disperse and the 

 fishery comes to an end. 



The Sprat. 



The sprat is found everywhere aiong the Lancashire and 

 Welsh coasts and in the Solway, but during the Bummer months 

 it is mainlv immature fish that one sees. About October 



