Distribution of Larval Plaice. 47 



rence, but directly proportional to the distance of the locality 

 from the coast and to its depth." Thus the growing plaice will come 

 under the influence of the trawl and be captured in largest numbers 

 on those grounds which are adjacent to the suitable gathering places 

 of the larvae. Our most recent knowledge of the distribution of 

 small (or young) plaice in Scottish waters is derived from the publica- 

 tions of Professor D'Arcy W. Thompson and Dr. Fulton. Professor 

 Thompson shows that small plaice are practically absent in our 

 deeper waters, and that, actually and relatively to the other sizes, 

 they increase in numbers as we pass to the shallower zones. Dr. 

 Fulton gives a detailed account of the occurrence of small plaice 

 within the different statistical areas. 



That the pelagic eggs of the plaice, as the embryo advances in 

 development, tend to sink to the lower water layers has been fully 

 shown in the tables already given. But even if this sinking of the 

 egg be doubted, the " Goldseeker " records amply prove that eggs 

 in the first stages of development also occur in the deeper water 

 layers. Any efforts made to trace the influence of the drift of the 

 waters on the fate of the eggs and newly hatched larvae must necessarily 

 take into consideration not only the movements at the surface but 

 also the direction and velocity of the deeper currents. 



The general movements of the cm'rents in the Northern North Sea 

 have recently been very fully investigated by the use of different 

 types of floating bottles. Dr. Fulton was the first to employ this 

 means of studying on a large scale the direction and velocity of the 

 sm'face currents on the Scottish Coast, while Captain Brown has, 

 by means of specially loaded bottles, added greatly to our knowledge 

 of the movements of the bottom currents. These experiments prove 

 the existence of a circular movement of the waters in the Northern 

 North Sea, the bottom currents moving in the same general direction 

 as the surface ones but at a slower rate. It may be stated roughly 

 that the drift of the water entering the North Sea from the west of 

 Orkney and Shetland turns southwards on the western side of the 

 North Sea,. then eastwards towards the Continent, and finally north- 

 wards along the coast of Norway. The average rate of the surface 

 water off the East Coast of Scotland is from 2 to 3 miles per day. The 

 general tendency would therefore be for pelagic eggs to be carried 

 southwards and eastwards, but Dr. Fulton has shown that in the 

 case of the plaice there is a compensatory northerly movement of 

 matm^e adults. Such is a broad statement of the general facts. 



In estimating the influence of the currents the fact must not be 

 ignored that plaice eggs are spawned only at particular seasons of the 

 year and in numbers only in restricted areas. It is therefore ob\dous 

 that local and seasonal variations of current, due to the configuration 

 of the land or sea bottom, the prevailing winds, and the volume of 

 the main inflowing stream, may play a very important part in deter- 

 mining the dispersal of pelagic eggs all spawned in relatively shallow 

 water in the vicinity of the Scottish Coast. 



Further, no doubt the time as well as the duration of spawning 

 have an intimate connection with the seasonal variations of current. 

 Dr. Damas has shown that saithe, for example, spawn in large numbers 

 on the Tampen at a time when there is a hydi'ogTaphic equilibrium 

 over that area. 



