TRANSACTIONS OF SECTION D. 



767 



(ii) Plymouth District. By W. L. Calderwood. 



Extracted from the Tables. 



Sole. 



Smallest mature $ 

 8i inches. 



Smallest mature 

 8 inches. 



Smallest mature 

 7 inches. 



Largest immature S 



10 inches. 

 Largest immature 2 

 9 inches. 



Plaice. 



Largest immature (? 



12 inches. 

 Largest immature ? 



11 inches. 



Lemon Sole. 

 Largest immature <? 



Largest immature ? 



7 inches. 



No immature males observed, 



Smallest mature $ 

 10 inches. 



Smallest mature '^ 

 11 inches. 



Smallest mature 

 7 inches. 



At Plymouth turbot and brill have become so scarce and expensive that I 

 have only been able to examine a few. All were males, and therefore of little 

 importance. 



Mr. Cunningham considers 12 inches a better size for the sole. In other respects 

 he appears to agree with the sizes I have suggested in the comparative table. 



Part III. The Protection of Immature Fish. 

 By J. T. CxrNNiNGHAM, M.A. 



I. The Limit op Size for each Species. 



My researches have been directed more to the question of the rate of growth 

 and to the age at which maturity is reached than to the size of specimens taken at 

 sea. 



I have found, in the case of the flounder, that of a large number of specimens 

 reared in captivity none became ripe when one year old, although a few reached 

 the size of the smallest mature specimens, i.e., a length of 7 inches. In the second 

 spaMaaing season from that in which they were hatched a proportion, viz., 19 per 

 cent., became ripe and spawned. The rest did not become mature at two years 

 old. 



The results of this research, which I wish to emphasise, are two. 



(1) That an adult or sexually mature fish is at least two years old, and more 

 probabl}' three years, ■while an average sized adult is usually four years old or 

 more. 



The importance of this fact is that it shows how easily the supply of a valuable 

 fish may be diminished by over-fishing. A turbot, for instance, produces a very 

 large number of eggs, from which comparatively few larvae safely pass through 

 their metamorphosis, and even after this the young fish have to find food and 

 escape enemies for throe or four years more before they reach the average size of 

 fish brought to market. 



(2) That the size of the smallest ripe fish is not the only point to be considered 

 in fixing the limit below which the young fish require to be protected. 



Assuming that a fish ought not to be killed before it has been able to reproduce 

 itself and leave progeny to take its place, it must be remembered that while one 

 specimen of a female flounder which is 9 inches long may be two-and-a-half years 

 old, and have already spawned once, another which is 10 inches long may be only 

 one-and-a-half year old, and have never spawned at all. 



The limit fixed should therefore, in order to exclude all immature females, be 

 somewhat higher than the size of the smallest (ripe) females observed. 



