of the Fishery Board for Scotland. Ixv 



long journeys before the spawning season, and in the great majority 

 of cases they move northwards along the East Coast against the pre- 

 vailing current. This northward migration is, doubtless, to com- 

 pensate 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 have been marked and liberated in the Firth of 

 Forth, or to the east of the Isle of May, were recaptured off the coast 

 of Aberdeenshire or in the Moray Firth. Some of them, indeed, 

 travelled to the Orkney Islands, the North Coast of Scotland as far west 

 as Cape Wrath, and several were caught again on the West Coast of 

 Scotland, a few as far south as Loch Inchard, Sutherlandshire, a 

 distance of nearly 260 miles from the locality of liberation. In some 

 instances these fish moved with great rapidity : for example, two 

 plaice liberated in the Firth of Forth, between Elie and Fidra, were 

 caught after 114 days at Loch Inchard ; one, liberated 20 miles east 

 of the Isle of May, was recaptured off Cape Wrath, a distance of 230 

 miles, after an interval of only 84 days. In like manner, many of the 

 adult plaice liberated off the coast of Aberdeenshire and in the Moray 

 Firth, or in the vicinity of Fair Isle, were recaptured on the North 

 Coast and the West Coast, one as far south as Dubh Artach, to the 

 south-west of Mull. 



These marking experiments also throw light on 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 

 live beside them in their natural condition on the fishing grounds. 

 The proportion of the marked fish recaptured thus furnishes an indica- 

 tion of the proportion of the natural stock which is within a given time 

 removed, and this proportion in many cases is much larger than might 

 be expected. Thus, of 960 plaice marked and liberated 20 miles east 

 of May Isle, no less than 632, or 65*8 per cent., were recaptured ; of 

 1227 liberated on Aberdeen Bank, which lies about 30 miles south-east 

 of Aberdeen, 724, or 59 per cent., were recaptured ; of a total of 823 

 marked and set free in the Firth of Forth, the number recaptured was. 

 483, or 58-7 per cent. ; and, even in the neighbourhood of Fair Isle,, 

 where 940 plaice were liberated, the recaptures numbered 461, or 

 48-9 per cent. In the four years, 1910 to 1914, of 7158 plaice marked 

 and liberated, 3721, or over 53 per cent., were recaptured, in the great 

 majority of cases by trawling. These figures give some indication of 

 the extent and intensity of fishing operations in the North Sea. 



The Influence of Marine Currents. 



As is indicated above, the part which is taken by sea-currents in 

 distributing the floating eggs and larvae of fishes may have an important 

 bearing on fishery problems. Sea-currents may profoundly influence 

 the migration of the adult fishes, the movement of the floating eggs and 

 young fishes from one part of the coast to another, and the movements 

 of the planlvton, or floating organisms, so important for the food of 

 fishes. Investigations were therefore undertaken to ascertain as 

 thoroughly as possible the course, direction, and rate of the surface 

 currents along the East Coast of this country, and throughout the 

 North Sea generally. For the investigation of the surface" currents, 

 a large number of small sealed bottles, suitably weighted to maintain 

 c 



