SEA-FISHERIES LABORATORY. 161 



the substance of the otoliths was made up of the modification 

 of calcium carbonate, known as aragonite. It contains about 

 98 per cent of CaC0 3 , the remainder being organic matter and 

 water.) 



During June the " sixpenny flukes " leave their foreshore 

 and very shallow- water habitat and migrate further out to sea. 

 In July and onwards they can be taken in the shrimp trawl-nets, 

 and their abundance there has been, for a long time, the 

 interesting feature in the life- history of the plaice from the 

 point of view of fishery regulation. A great deal of attention 

 has been devoted to this question in Lancashire : whether or 

 not shrimp- trawling does more harm to the general fishing 

 industry than it is worth ? From the beginning of their 

 period of control the Lancashire Sea-Fisheries Committee made 

 many observations on the relative abundance of plaice and other 

 fishes in the catches made by the shrimp- trawlers in their 

 district. The late Superintendent, R. A. Dawson, devised a 

 special form of the shank-net, designed to permit the capture 

 of shrimps while allowing young, flat fishes to escape, but this 

 instrument never became adopted. In 1899 the Committee 

 applied to the Board of Trade (which was then the Central 

 Fishery Authority in England) for confirmation of a By-law 

 restricting trawling by fine-meshed nets in the important 

 nursery ground off the estuary of the Mersey, but this measure 

 was very seriously opposed by the local fishermen, and the 

 Board refused to sanction it. Since then the question has not 

 been raised again. 



Table 11, gives a summary of the results of the measure- 

 ments of plaice made in the experimental hauls carried 

 out by the officers of the Committee on the Mersey grounds 

 during the period 1908-1913, and there is a detailed report on 

 a series of observations made by Capt. G Eccles during the years 

 1899-1920, which gives a very fair idea of the conditions on 

 this nursery ground. First, as to the sizes of the plaice taken : 



