BARENTS SEA IN AUGUST, 1907. 93 



grounds actually exist, from which the stock of the outer grounds may 

 be renewed. 



If the majority of the eggs and larvre are carried by currents to 

 regions in which they must naturally perish, as Hjort and Dahl 

 (loe. cit.) have shown to be the case on parts of the Norwegian coast, 

 it is evident that the fishery can only flourish so long as the present 

 stock, accumulated through a great number of years, continues to be 

 sufficiently abundant to pay for its capture. 



It is not difficult to imagine that there may have been a period 

 when the central grounds of the North Sea were inhabited by a plaice 

 population, of which at least the majority of the individuals were 

 mature ; and, had we a curve of measurements of that period, the 

 mode would conceivably have exceeded the average size at which the 

 fish were first mature, by an amount as great as may now be found in 

 the virgin waters of Northern Europe. 



One of the earliest effects of fishing on any ground is to reduce the 

 number of the large fish, and consequently lower the average size ; 

 that is to say, representing this effect on a diagram to compare with 

 Figs. 2 and 3, the mode will recede to the left, and approach the size 

 at which the species becomes mature. 



If it is allowed that an accumulation of mature plaice once pre- 

 ponderated in the central North Sea, it will be obvious that the retro- 

 gression of this modal size to its present position (36-37 cm.) helow 

 the average size at first maturity (39-40 cm.) must have been effected 

 gradually by the influence of man, for no serious natural enemy of 

 large plaice in the North Sea is recognised, whilst the intensity of 

 fishing is known to be very great. 



Hence it is conceivable that if intense fishing continues, the modal 

 size of the plaice will imperceptibly recede to even lower limits, and a 

 period must arrive, if it is not already with us, when the supply of 

 eggs, and consequently young fish, seriously suffers. 



SUMMAEY. 



In this preliminary investigation of the plaice on a bank in the 

 Barents Sea the following were among the chief features noted : — 



1. The population consisted almost entirely of mature fish, thus 

 presenting a marked contrast to the conditions prevailing at the 

 present day in the central parts of the North Sea (Dogger Bank, etc.). 



2. The " average size at first maturity " for the females appears to be 

 approximately the same (39-40 cm.) in the Barents Sea as in the 

 central parts of the North Sea : but, whereas in the Barents Sea the 



