SEA-FISHERIES LABORATORY. 151 



There is a fairly well-marked seasonal variation in length. 

 Thus, taking the Mersey Estuary, we get : 



May 18-21 cms. 



June ... ... ... ... 17-20 cms. 



July 18-21 cms. 



August 20-24 cms. 



These are also the shortest half -ranges. The differences 

 are due to the natural growth of the plaice and also to successive 

 waves of migration of small fish from the more crowded, very 

 shallow waters, to the sea just offshore. This we refer to in 

 the section dealing with migrations. 



The Nursery Grounds. 



These we refer to when dealing with the life history of the 

 plaice in the Irish Sea. 



