SEA-FISHERIES LABORATORY. 105 



size of the plaice further south results from the practically 

 unrestricted exercise of this method of fishing. 



The size of the plaice captured also suggests some 

 doubts as to the accuracy of the generally accepted theory 

 of the life history and migrations of that fish. It is 

 usually stated that the mature plaice inhabits and spawns 

 in comparatively deep water (10 to 20 fathoms), that the 

 fertilised eggs and larva? drift inwards towards shallow 

 water, and that as the fish grows it migrates outwards 

 towards the 20 fathom line. The observations made in 

 Luce Bay, where plaice of 20 inches in length were found 

 close in towards the shore in water of six fathoms and less 

 in depth, show, however, that the above distribution is not 

 universal, and that there is no necessary relationship 

 between the depth of water and the size of the fish on the 

 bottom.* Large plaice are found in Luce Bay because 

 trawling is prohibited there and they are not interfered 

 with. It is, however, reasonable to suppose that the 

 absence of mature plaice on the inshore grounds of such 

 an area as the Lancashire and Cheshire District is due to 

 the great extent to which these grounds have been fished 

 over. The amount of fishing on the inshore grounds is 

 much greater than in deeper water, and the fish on the 

 latter area are much less disturbed. The effect of this 

 extensive fishing inshore has been to reduce greatly the 

 average size of the plaice present, and it is to be noted 

 that investigations into the life history of this fish have 

 been made in comparatively recent times — since the ex- 

 ploitation of the inshore grounds by the trawlers on the 

 modern scale has taken place. This effect of trawling in 

 reducing the average size of the fishes present on a 

 ground is well known, and was first demonstrated by 



* Our observations, however, have been confined to the months of 

 October and November. Possibly the large plaice may migrate from 

 the Bay in winter and during the spawning season. 



