SEA-FISHERIES LABORATORY. 197 



tion with a much greater range of dispersion — in otliei 

 words, the medium and large plaice are relatively more 

 abundant than they are on the other grounds. 



A notable feature of these distributions is also the 

 presence of double modes in most of the curves formed 

 from them. In June, July, and August the curves have 

 single modes, that is, the population has, so far, been one 

 which is nearly stationary except so far as it is being 

 recruited from the nursery grounds close inshore. This 

 modal length — 19'5 to about 20'5 — approximates closely 

 to that of the other fishing grounds, and the increase is 

 that due to the natural growth of the fish during the 

 season June to August. The amount of growth is rather 

 small, but we see from Table XXV that the value of the 

 length-weight coefficient h on this ground is significantly 

 less than it is on the Lancashire and Cheshire grounds, 

 that is, the fish are not in such good "condition," and are 

 presumably growing less rapidly. From October 

 onwards, the curves become bi-modal, and the mean values 

 of the mode for these latter months are about 19 and 28. 

 Clearly we have an extensive immigration of plaice into 

 the Beaumaris-Red Wharf area from the grounds to the 

 North-East, and this consists of the larger fish from the 

 latter regions. This immigration establishes a hetero- 

 geneous population, which is indicated by the double 

 modes of the distributions for these months. The lower 

 mode is that typical of the native population of the grounds, 

 while the higher one is that of the immigrant population 

 from the other fishing grounds. The immigration can 

 clearly be traced in the figures for October. The curve 

 becomes uni-modal, and the proportion of fish below the 

 mode greatly increases — smaller fish are pouring into the 

 area. 



This migration into the Red Wharf Bay area is 



