190 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



the shrimp trawls vary in modal length between 7 and 

 8'b cms. The dispersion is very small. 



After March, the composition of the catches becomes 

 more complex, and we are able, to some extent, to see in 

 the figures the influence of the three age-groups of which 

 the plaice population on a "nursery-ground" is made up. 

 In April, the frequency curve becomes bi-modal, and 

 there are cusps at about 7 and 14 cms., that is, age groups 

 and I are represented in the catch in nearly equal pro- 

 portions. The May and June figures are unreliable, but 

 in July the first three age-groups are clearly represented 

 since there are very distinct modes at 5*3, 11'6, and 

 194 cms. The 5*3 cms. cusp obviously represents age- 

 group 0, that is, the plaice born in the same year, and 

 which have attained this length during the interval March- 

 July. The 11 '6 cusp represents age-group I, that is, the 

 plaice born the previous year, and which have completed 

 about one and a half seasons of growth, while the 19'4 cms. 

 cusp is that formed by age-group II, fish of 2 \ years of 

 age. In September and October, age-groups and I are 

 represented by the modes at 7*7 and 73 cms., and those at 

 15 '6 and 13 cms. Plaice have now completed their 

 season's growth, and Group shows the modal length of 

 about 7 cms. Group I has, doubtless, a modal length of 

 about 13 to 14 cms., but the precise position of the cusp 

 representing this yearly group in a complex curve is 

 certainly affected by the fishing action of the net, and we 

 cannot be sure that the sample is a representative one so 

 far as fish of this age are concerned. 



Plaice of less than 3 cms. in length are hardly ever 

 caught in the shrimp-trawl net, and, indeed, their habitat 

 does not seem to be that of the fish of lengths near to 

 7 cms. They are, however, present in great numbers in 

 the very shallowest water near the shore, and they may 



