ON THE MIGRATIONS AND THE GROWTH OF PLAICE. 1 53 



On the Northumberland coast, therefore, the small plaice of 

 the sandy pools gradually pass out to the immediate slightly 

 deeper waters of the bays, where they spend the immature 

 phases of their lives, and do not migrate, so far as we can see, 

 far along the coast. Approaching maturity impels them 

 when 4 to 5 years old to migrate into the deeper extra-terri- 

 torial waters, and even there they appear to have the tendency 

 to migrate into deeper and deeper water as they become older 

 and larger. This in itself would serve to correct to some 

 extent the general southerly and westerly movements of the 

 ova and larvae. Some of the mature plaice certainly do find 

 their way back to the same or other inshore waters, impelled 

 more than probably by recollections of sandeels, but such a 

 return cannot be said to be more than rare. 



But we look to the international researches to show if there is 

 a distinct or even a general relationship between size and depth, 

 and if this may be looked upon as the only impulse which tends 

 to move the plaice in a definite direction in the North Sea. 



Population. — Following a method which has been adopted 

 before in the case of such experiments, a calculation may be 

 offered to give an indication of the number of the resident 

 population of plaice of from 2 to 4 years old. We marked 

 472, and we recovered from the catches of fishermen in the 

 district 50. This is, allowing slightly for loss, one-ninth part, 

 and may be taken therefore to represent approximately the 

 catching power of the inshore fishermen. As near as we can 

 gather the fishermen caught in the inshore waters for the year 

 ending June 30th, 1904, 440 cwts. of plaice. The population 

 of plaice of the inshore waters from about 7 to 14-in. long 

 may be said to be therefore 3,960, or say 4,000 cwts. If the 

 average weight of the fish be, say ^-Ib., the population in 

 numbers is about 900,000. Considering the large proportion 

 obtained from some of the districts this number will probably 

 be found to err by being too large rather than too small*. 



* If our figure underrates tlie oatohmg power of the fishermen, it is also true that 

 many more plaice are caught than are sent to market or used for crab bait ; and as a 

 matter of fact our labelled fish were sometimes caught by Others than professed 

 fishermen. 



