SEA-FISHERIES LABORATORY. 137 



symmetrical curve would not, strictly speaking, be the 

 normal curve of error, deduced from the binomial 

 expansion, with branches extending to infinity in either 

 direction, but rather Pearson's " Type II," that is, 



/-, x 2 \ m 



which is symmetrical, but limited in both directions. 



Leaving for further investigation the question of the 

 application of a theoretical frequency-curve, we may 

 consider the modal sizes of plaice of Age-Groups I, II, 

 and III, inhabiting the coasts of Lancashire and North 

 Wales. It is quite impracticable to attempt to estimate 

 the ages of fish older than these, for such plaice are so 

 sparingly represented on the in- shore fishing grounds as 

 to make any such estimate subject to considerable error. 

 During the autumn there is indeed an immigration of 

 large mature plaice into shallow water, so that fish 

 belonging to Age-Groups IY and Y may be taken in 

 Barrow Channel and off the coasts of the North Welsh 

 counties, but the number of such plaice examined is far 

 too small to be capable of statistical treatment. It will 

 also be seen from the tables that fairly large plaice may 

 be taken on the banks off the North of the Isle of Man, 

 in the Firth of Clyde and in Luce Bay, and the results 

 of several hauls on these grounds are given for tlie 

 purpose of comparison with the Lancashire fishing area. 



The plaice caught on the latter grounds belong almost 

 entirely to Age-Groups 0, I and II. Barrow Channel, 

 the shallow water in the estuaries of the Ilivers Lime and 

 Wyre, the grounds off Nelson Buoy, and the Hock 

 Channel in the Mersey area may be taken to represent 

 the Lancashire in-shore area, and there is comparatively 

 little difference in the modal sizes of the plaice captured 

 on these grounds. The table on p. 180 may be very 

 briefly summarised as follows: — 



