55 



At station VI. on the north side of the Forth the plaice arrive 

 in April to June, reach a maximum from July to September, and 

 during October to December suffer a loss which becomes sharply 

 marked in the early months of the year. This is also the North- 

 umberland experience, but it is evident that a large number of 

 plaice remain in the greater depth just outside that of the North- 

 umberland experiments. 



The figures are interesting otherwise as indicating the method 

 of immigration and emigration, but the point which it is wanted 

 here to emphasise is better brought out in three stations of the 

 Moray Firth, the stations of Burghead Bay. The lines trawled 

 over were parallel to one another and with the shore, and the depths 

 respectively of the three stations were a 10, b 10-20, c 20-34 

 fathoms. 



The plaice caught per hour's trawling were as follows : — 



The outward migration from the shore is correlated with a 

 gathering of plaice in winter in depths of about 10 fathoms. It 

 is also manifested at the greater depths, but is somewhat later 

 in its incidence, and the change to the winter maximum offshore 

 is clear. The mean size of the plaice at station " a " is 26 cm., 

 of " b " 27 cm., and of " c " 34 cm., and this indicates that the 

 inshore congregation is followed by an offshore segregation, a 

 fact which is further illustrated by the catches in deep water off 

 the Forth and in the deeper water of the Moray Firth. The 

 emigration is partial and not to a great distance, from, say, about 

 2-5 fathoms to about 10-15 and so on, and an intimate relation- 

 ship is thus maintained to the greatest depth. 



Besides this inshore and offshore movement, the latter to 

 increasing distances with age and size, another tendency is at 

 work which brings about a determination at all stages of the plaice 

 at the north end of the school, or, in other words, the contranatant 



