50 Fishery Board for Scotland. 



junction with the record of capture of the mature plaice it confirms 

 the view that some plaice may spawn on the relatively shallower 

 Bergen and Viking Banks. 



While the occurrence of extremely small plaice on the beaches 

 is not indicated, the chart shows at a glance how the " small " plaice 

 (in the market sense), which are immature, are much more restricted 

 in distribution than the large plaice. On the other hand, although 

 plaice eggs are found as widely distributed as the mature or large 

 plaice, the chief spawning areas lie within the area of distribution of 

 the small plaice. Mature plaice are therefore more numerous in the 

 shallower zones during the spawning months. This statement is 

 confirmed by the records of the seasonal distribution of large plaice 

 within the different statistical areas. The spawning grounds of the 

 mature plaice are more localised than their feeding grounds. 



If a chart showing the direction of the prevailing currents in the 

 Northern North Sea is superimposed on the chart of distribution of 

 the pelagic plaice eggs it is seen that the principal spawning areas 

 lie within the western periphery of the south-going current. It is 

 true that the south-going current tends to carry the passively floating 

 plaice eggs and the helpless larvae in that direction, but it is also true 

 that there is a general movement northwards of adult plaice which 

 compensates for this southerly drift. 



The contour of the East Coast of Scotland is such that the main 

 south-going current is shouldered off at Noss Head to impinge on 

 the south shore of the Moray Firth, east of Lossiemouth. The main 

 spawning grounds for plaice in the Moray Firth lie to the westwards 

 of the main stream within the triangle so formed. Eggs spawned in 

 this area are therefore in an eddy and are not directly influenced by 

 the main current. Again, the south-going ciu-rent is shouldered off 

 the coast at Kinnaird Head and Buchan Ness, whilst there is a further 

 divergence of the current, especially in the bottom layers, in the 

 neighbom-hood of the " Long Forties," so that the western part 

 branches sharply to the southwards and south-west, forming a very 

 decided set towards the Firth of Forth and the coasts lying south of 

 it. It has been shown, however, that the chief spawning localities 

 on the East Coast of Scotland lie within the triangle, the base of which 

 extends from Kinnaird Head to Berwick and the apex of which lies 

 in the vicinity of the " Long Forties." The chief spawning localities 

 for plaice on the Scottish East Coast are thus so situated that the 

 passive eggs are carried a minimum distance from the localities in 

 which they were spawned. 



There is apparently little or no correlation between these favoured 

 spawning places and the temperature and salinity of the water, 

 although these factors in themselves are not unimportant for the 

 welfare of the species. This is mentioned because the Dutch in- 

 vestigators have shown that in the Southern North Sea by far the 

 most important spawning area for plaice is in the south-western 

 corner where the temperature and salinity are high. But even in 

 this case, too, these factors of salinity and temperatm'e may be of less 

 importance than the influence of the prevailing current on the welfare 

 of the species since the eggs and larvae are gTadually carried eastwards 

 towards the great nursery for plaice in the south-east corner of the 

 North Sea. 



