SEA-FISHERIES LABORATORY. 189 



seek to explain the connection between the movements of 

 fishes and changes in the hydrographical conditions. 



(b) Mersey Shrimping Grounds. 



These grounds, the channels and " gutters " through 

 the banks lying outside the Estuary proper, and the 

 shallow water margins of the banks themselves, constitute 

 a nursery for plaice and other small fishes, and it is from 

 this point of view that they derive their interest. But 

 we find in much the same region very extensive " small- 

 fish " grounds ; the larger channels, Rock Channel, Horse 

 Channel, &c, and the shallow water off the banks, harbour 

 plaice of sizes varying, for the most part, between 18 cms. 

 and 30 cms. There are frequent migrations of plaice from 

 one part of the Mersey grounds to other parts, and catches 

 made with the small-meshed net used in the shrimp 

 trawls frequently sample shoals of fish of the larger sizes. 

 On this account the interpretation of the statistical data 

 is sometimes very difficult. 



The catches made by means of the shrimp-trawl nets 

 are summarised in Tables XIX-XX. They are, as a rule, 

 large, and with some exceptions they provide us with a 

 fair picture of the distribution of the smaller plaice in 

 the Mersey Area. The exceptional months are May, June, 

 and August, and the figures seem to show that the nets 

 were fishing among shoals of plaice of the larger sizes. 

 The numbers caught during these months are also rather 

 small, and we may, therefore, regard the results as 

 anomalous and likely to be modified to a large extent by 

 further experiments. 



The modal lengths of the plaice caught arc given 

 in Table XXIV. The results for the winter months, 

 November to March, inclusive, are all very similar; at 

 ill is time of year the great majority of plaice caught in 



