SEA-FISHERIES LABORATORY. 209 



growth there are practically no plaice below 4 cms. in 

 length : this limit represents the minimum size to which 

 plaice grow in their first year of life. Also there are 

 practically no plaice, in the first year, of lengths greater 

 than about 12 cms. ; this limit represents the maximum 

 size to which the fish grows in Lancashire waters during 

 its first year. So, also, the curve for Group II appears to 

 be a natural one, for plaice between about 12 and 30 cms. 

 in length would be caught by a 6-inch trawl-net in very 

 much the proportions in which they actually exist on the 

 fishing grounds. It is also probable that the curve for 

 Group III is a fairly accurate one, but that for Group IV 

 does not seem right : it ought to have a greater dispersion, 

 so that the frequency at the mode ought not to rise so high 

 as is shown in the figure. The catches made do not, in 

 fact, really represent the frequencies of this age-group in 

 Lancashire waters, because plaice of over four years in 

 age are relatively scarce on these fishing grounds, and 

 the samples so far obtained are not really representative 

 ones. The curve for Group IV ought to be flatter, just as 

 that for Group I ought to be steeper. This modification 

 is suggested by the curves drawn in broken lines, and it 

 is hoped that further study of the age-groups will bear 

 out the suggested alteration of the modal lengths so far 

 actually observed. 



We may, therefore, summarise the results of this 

 section as follows : — 



Modal Lengths of Plaice in Lancashire Waters : - 



Plaice of Age-Group (that is, over and under 



1 year of age) are, on the average, 7 cms. 



(2J in.) long. 

 Plaice of Age-Group I (that is, over 1 and under 2 



years of age) are, on the average, about 13 cms. 



(5J in.) long. 



