of the Fishery Board for Scotland. 6 1 



Owing to the great natural fluctuations that occur, as shown, for 

 example, in the means for the second period, when no plaice fry were 

 added, one would not expect that the fluctuations in abundance in the 

 years when plaice fry were added Avould be closely related to the 

 number of fry liberated in any particular year, for the increase due to 

 this cause is liable to be masked by the extent of this natural 

 fluctuation. In the twelve years for which annual averages exist, four 

 of tlie six highest were in the first period of six years and two in the last 

 six. The highest of all was in the year when the greatest number of 

 plaice fry were added, viz., 1901, when the average was 174 per hour 

 and when 51,350,000 fry were liberated. The second highest was in 

 1905, when no fry were added, the average being 1 1 2 per hour. The 

 third highest was in 1896, viz.. Ill "4 per hour, when 4,100,000 fry were 

 added ; the fourth highest was in 1898, viz., 95-6 per hour, when 

 19,200,000 fry were placed in the loch; the fifth highest, 53i, per 

 hour, was in 1900, when the number of fry liberated was 30,590,000 ; 

 the sixth highe.st, 37 3 per hour, was in 190.3, when no fry were added. 



The period of thirteen years over which these experiments have 



extended is considerable, and ought to go far to equalise the 



natural fluctuations ; and I think it is reasonable to conclude that 



the greatly increased average abundance of the young plaice in the 



first six years was mainly due to the liberation of the 142,880,000 fry of 



the plaice in those years, and that, on the other hand, the decrease in the 



abundance of young plaice in the last six years was mainly owing to the 



fact that no plaice fry were added to the waters of the loch in that 



period. On theoretical grounds alone it would be an astonishing thing if 



the addition of the immen-se number of plaice larvae mentioned to the 



waters of a long, narrow, and confined loch like Lochfyne should 



produce no increase in the numbers of young plaice a few months 



older than the larvae added. And if that is the effect in Lochfyne, it will 



also be the eff'ect elsewhere, though the natural fluctuations may conceal 



it. With regard to the extent of the influence of the liberation of the 



fry on the abundance of the young plaice during these experiments, 



the difference in the averages in the two periods shows that 



the plaice were more than doubled in number.* There is one 



cmsideration, however, that ought not to be lost sight of. 



On the East Coast, and in the North Sea generally, there have 



been complaints of the diminution of plaice zd recent years, and 



this was proved to have occurred in the Firth of Forth from the trawling 



experiments of the " Garland." There is not suflftcient information 



with regard to the Clyde area to show whether the same change is 



occurring there, but if it is — if the adult plaice are decreasing and have 



been for some years decreasing— -it might account, in part at least, for 



the reduction in the average catch of the young plaice in Lochfyne in the 



second period of the experiments. It would therefore be desirable to 



have a third period in the experiments, namely, a series of years during 



which large numbers of plaice fry were added to the waters of the loch, 



as in the first period, and to ascertain the effect of this on the abundance 



of the young plaice on the beaches. 



* The above conclusion with regard to the result of the experiments in Loch- 

 f j'ne — that the number of plaice on the beaches was more than doubled bj' the 

 addition of the artificiallj'-hatched fry— has been confirmed bj' an elaborate 

 mathematical investigation of the fluctuations in the difl'erent jears, which was 

 kindly made by Miss R. M. Lee, of the Marine Biological Laboratory, Lowestoft, 

 after mj- paper had gone to the printer. — T.W.F. 

 E 



