of the Fishery Board for Scotland. 



Ivii 



however, to which attention may be meanwhile directed. The first 

 relates to the migrations of the plaice. The numbers of plaice which 

 were marked and liberated and the number and percentage of those 

 recaptured in the three years are as follows : — 



Some of those liberated in 1910 are still being obtained, as well as 

 those of 1911. With reference to the movements of the marked fish, 

 it has been found that a distinction must be drawn between those 

 which have not reached the size of maturity and those which exceed 

 that size. The former do not, as a rule, move far from their ordinary 

 feeding grounds, and they do not appear to take any very definite direc- 

 tion in such movements as they make ; the latter, on the other hand, 

 undertake often long journeys before the spawning season, and in the 

 great majority of instances they move along the East Coast in a northerly 

 direction, that is to say, against the prevailing current. This mic;ra- 

 tion is doubtless to compensate for the southerly drift of the floating 

 eggs and larval fishes from the localities where spawning takes place. 

 Thus many of the adult plaice which had been marked and liberated 

 in the Firth of Forth, or eastwards of the Isle of May, were recaptured 

 off the coast of Aberdeenshire, or in the Moray Firth ; many of those 

 liberated off the coast of Aberdeenshire were again taken in the Moray 

 Firth, or on the North or West Coast, having in such cases traversed 

 the Pentland Firth. In like manner many of the adult plaice liberated 

 in the Moray Firth, or in the vicinity of Fair Isle, were recaptured at 

 the Orkney Isles, or on the North Coast and the West Coast. It is 

 interesting to have determined that the plaice in the Moray Firth 

 are recruited to such an extent from the grounds off the East Coast, 

 and even from the Firth of Forth, by the migration thither of the 

 adult fish. It is also fairly certain, though direct experimental 

 proof is lacking, and indeed could hardly be obtained, that the 

 grounds to the south are recruited by supplies of floating eggs and 

 larval plaice carried from the Moray Firth by the prevailing current. 



Another point on which the marking experiments throw light is the 

 intensity of fishing operations. There is no reason to suppose that 

 the marked plaice are either more liable or less liable to capture than 

 those which exist beside them in their natural condition on the 

 grounds. The proportion of the marked fish recaptured thus offers an 

 indication of the proportion of the natural stock which is within a 

 given time removed by fishing operations, and that proportion is 

 larger than might be expected. Thus of 100 plaice liberated at a 

 locality twenty miles east of the Isle of May in March last year, 61, 

 or 61 per cent., have been already recaptured. Of 300 marked and 

 set free in the Firth of Forth, 102, or 34 per cent., have since been 

 caught again — 76, or 26 per cent., outside the limits of the Firth, and 

 the remainder, or 8 per cent., within it. 



1910, 

 1911, 

 1912, 



Marked, 

 1,915 

 1,733 

 2,165 



Kecaptured. 



964 

 777 

 593 



Percentage. 



50-3 

 44-8 

 27-4 



Sea Currents and Fishery Problems. 



As above indicated, the part taken by marine currents in distri- 

 buting the floating eggs and larvse of the food-fishes is of importance, 



