146 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



ence. But there are no figures for months prior to July. 

 The part of the curve drawn does, however, indicate that 

 the plaice population differs from that of the other two 

 areas. We know that the fishery in this part of the 

 district is an autumn and winter one, the fish immigrat- 

 ing into the in-shore waters off the North Welsh coast 

 late in the year. The fish do not appear ever to have 

 been in as good condition as those in Barrow Channel 

 during July, but they retain a high average weight until 

 late on in the year, when the condition of both Barrow 

 Channel and Rock Channel has fallen below the mean. 



6. INFLUENCE OF SIZE OF MESH. 



We should be able to find out what range of sizes of 

 fish would be caught in trawl-nets of different sizes of 

 mesh, by making a sufficient number of trial hauls; and 

 this kind of information is so important, practically, that 

 it is rather surprising that it has not been obtained long 

 before the present time. A number of such comparative 

 hauls were made in the earlier years of the Committee's 

 work, but I think the results are far too indefinite and 

 inexact to be of much use. It is quite absurd to describe 

 a catch of fish as consisting of so many over, say, 8 inches 

 in length and so many under 8 inches, for one cannot 

 say how far below or above the standard size the fish 

 were. It is only by measuring each fish taken, and then 

 exercising some care in the calculation of probable 

 average or modal sizes, that results capable of standing 

 criticism can be obtained. I do not think that very good 

 results can be obtained from the use of a double net, a 

 net of 4-inch mesh, say, outside one of, say, 7-inch mesh. 

 Obviously the wide meshed net would not make the same 

 catch as if it were used alone, for the draught of water 

 through it would be diminished by the small-meshed net 



