49 



immature and spent fish, which leave about October or November 

 and return about June. It was found, however, that one or two 

 of the older fish may remain during the winter, as was proved by 

 trawling at Alnmouth in January, April and May. 



A consideration of the rarer groups serves to indicate the 

 nature of the annual invasion of the more common species. They 

 are all summer visitors, and all include young and adult fish. 

 The complete or practically complete disappearance from the 

 shallow waters along the coast shows that a seasonal migration 

 takes place which affects all. In all cases the Northumberland 

 waters almost to the shore present every stage from the young 

 to the old, although not as a rule reaching the maximum size. 

 The conclusion is inevitable therefore that if the young do not 

 migrate far they are joined by larger, older fish, and some of the 

 latter may remain in shallow Avater even during the winter. The 

 main population takes part in the seasonal migration, which 

 follows so closely the rise and fall of the temperature of the sea. 

 The degree of the retreat and the advance is thus correlated with 

 size and strength. Now, in addition to this movement there 

 appears to be another or a modification of the seasonal migration 

 which brings about the distribution which we have found to 

 characterise the different species. 



The gurnard and the angler, although not so valuable as the 

 foregoing, yet occur in sufficient numbers to be of importance. 



Gurnard . — In 1920 the catches arranged so as to bring out 

 the numbers with relation to size are : — 



TABLE XVII. GURNARD. 1920. 



The mean size of the young at Blyth on July 29th was 10 

 and 15 cm. ; at Alnmouth, 1G-5 cm. ; in August at all the bays, 

 17-5 cm. ; and in September at Druridge, 19-5 cm. 



The distribution is like that of the dabs, and it agrees in this 

 respect with the results of past years. During the summer each 

 year gurnards arrive in the inshore waters in variable numbers, 



