40 



1. These species are not sedentary but enter and leave the 

 regions in question, and there is a conspicuous annual immigration 

 and emigration. In the case of plaice the minimum condition is 

 reached in February and March, and maxima are usually apparent 

 in June and August and September. Dabs almost entirely dis- 

 appear from the shore waters from November to April, and reach 

 a summer maximum in July or August, and a double maximum 

 is sometimes evidenced. 



2. Large numbers of immature and small numbers of those 

 approaching maturity and spent fish take part in the periodical 

 seasonal migrations. 



3. The annual inshore migration presents the peculiarity 

 that the plaice of all sizes predominate in the northern part of the 

 area, and the dabs in the southern, and finer analysis shows that 

 what is true of the district as a whole is true also of the sub- 

 divisions. In each bay it has been found that the plaice tend to 

 the north end, and the dabs to the south end. It will be observed 

 that in chart 8, which illustrates the catches of the fishermen 

 in the respective areas with some degree of overlapping that the 

 distribution is equally well brought out, that is to say, that the 

 catches even by line illustrate the general distribution and relative 

 proportions of the species. 



Our trawling experiments have reference therefore to a 

 fluctuating population, subject to daily movements with relation 

 to tidal and other influences and to a conspicuous annual seasonal 

 migration, associated with temperature changes. Obviously the 

 fish cannot move in winter inshore for our trawling has been done 

 close to the shore, and it may be presumed therefore that they 

 movo offshore or into estuaries. This population of plaice and 

 dabs is recruited each season by arrivals from the spawning grounds. 

 Our results therefore bear witness to the success of the spawning 

 seasons and of the conditions of growth and food supply at the 

 size when from 10 to 15 cm. (4 to 6 inches) they are liable to be 

 caught in the trawl. At these sizes they are in their second and 

 third summers for tho most part and are already, as the evidence 

 shows, undergoing the seasonal change of position. It will be 

 seen that with increase of size and strength the seasonal migra- 

 tions become more and more extensive. 



