374 



NORTH SEA INVESTIGATIONS. 



We are aware, from Cunningham's researches on the rate of 

 growth, that this varies with the size in different species ; and from 

 the remarks of the same author on the plaice {supra, No. 2, pp. 99, 

 100) it appears that the same principle is applicable to local varia- 

 tion of size within the limits of one species. Hence it would appear 

 that local variation in the size at which sexual maturity is reached 

 is explicable by, or implies, variation in the rate of growth, and 

 involves no local difference in the age"^ at which fish spawn for the 

 first time. 



Size Limits for the North Sea District.— The following measure- 

 ments are intended to represent the average sizes at which the 

 female spawns for the first time in the North Sea district, so far 

 as such are ascertainable from observations made during, shortly 

 before, or soon after the spawning season : 



Turbot . . . . .18 inches. 



Brill 15 



Common sole . . . .12 



Plaice ..... 17 



Lemon sole . . . .12 



Halibut . . . . . 36 „ (provisional), 



Common dab .... 7 

 I have not paid much attention to the common dab {Pleuronectes 

 limanda) ; the smallest ripe female I have seen measured 6 inches, 

 and the largest immature female, during the spawning season, 

 9 inches. Flounders (P. flesus) and long rough dabs {Hippo- 

 glossoides limandoides) have not been available in sufficient numbers 

 for a satisfactory conclusion. The same applies to the megrim 

 {Rhombus megastoma), which is rather a rare fish on the grounds 

 usually worked by Grimsby trawlers, and the witch (P. cynoglossus) ; 

 but it is worthy of note that twelve female witches of 12 and 13 

 inches and two of 14 inches were immature, whilst one of 14 inches 

 was three parts ripe. Hence it seems likely that the fish does not 

 spawn at so small a size (12 inches) as on the west coast of Ireland. 

 I have never seen a sand or lemon sole {Solea lascar is) , and only one 

 solanetto {S. minuta) and scald-fish {Arnoglossus laterna) in the 

 Grimsby district. None of the remaining British Pleuronectids, 

 the topknots, have been met with. 



The following tables are abstracted from my records, and comprise 

 only the fish at the critical sizes examined between the dates 

 specified. It will be understood that all larger fish examined were 

 found to be mature, the converse holding good in the case of smaller 

 fish. 



* Allowing for the individual variation in one locality which Cunningham has shown to 

 exist in this feature {supra, No. 3, pp. 224, 225). 



