NORTH SEA INVESTIGATIONS. 373 



season, includes both large and rather small fish — say from the full 

 size down to the smallest size of mature males, — the limit of size 

 which divides mature from immature females will be found to prac- 

 tically separate the two sexes. Thus most of the larger fish will 

 be mature females, and most of the smaller ones will be mature 

 males, with a sprinkling of immature members of both sexes. This 

 is in complete accord with Fulton^s observations on the distribution 

 of fish on the spawning grounds (Rep. S. F. B., 1890, 178), and it is 

 noteworthy as an impediment in the way of the rigid application of a 

 size limit based on the condition of the larger sex. But it is not of 

 the highest importance, since the number of small fish in such cases 

 is, by comparison, insignificant (thus following the well-known pro- 

 portionate abundance of the sex), and it is only applicable to such 

 species as show a marked change of habitat in apparent relation to 

 the spawning instinct, and is variable within the limits of a species 

 according to locality."^ 



Local Variation. — A comparison of the results obtained by work 

 on the different coasts of Great Britain suggests a speculation on 

 the rate of growth in relation to maturity. 



Thus T understand from Messrs. Calderwood and Cunningham 

 that at Plymouth the plaice spawns at about 10 inches, a marked 

 contrast to the North Sea or even the west of Ireland conditions. 

 Again, Cunningham has found mature lemon soles {supra, No. 3, 

 p. 244) about as small as any which I met with on the west of 

 Ireland. With regard to the common sole, the limit proposed for this 

 district and for the west of Ireland is held by Mr. Calderwood to be 

 equally applicable to the Plymouth district, whilst Mr. Cunningham 

 would put it only a trifle lower. 



Now soles appear to be much the same size on all three coasts, 

 lemon soles are much larger in the North Sea than in the other 

 districts, and according to Cunningham {supra, No. 2, p. 100) 

 plaice are much smaller at Plymouth than in the North Sea. West 

 of Ireland plaice appear to be intermediate in size, but in this respect 

 approach the North Sea rather than the Plymouth fish, though, as 

 I had not much material on which to base my Irish limit for this 

 species, this is not of much importance. 



We see, therefore, that where there is agreement in the size of 

 fish of a species in any two or more districts, there appears also to 

 be agreement in the size at which sexual maturity is reached, and 

 that when there is variation maturity is reached at the smallest size 

 in the district where the species is smallest. 



* £J. g. it appears to apply to turbot on the Dogger, whilst on the eastern grounds 

 spawning and immature turbot may be caught together, the latter far exceeding the 

 former in number. 



