498 REPORT ON TRAWLING AND OTHER INVESTIGATIONS 



(16| inches). The range of variation is therefore from 13 to 16 cm. (5 

 to 6 inches). For the North Sea specimens the same range was found 

 to be 12 to 14 cm. 



" According to Dr. Fulton,* all plaice probably spawn at the same age, 

 and the difference in size is simply a difference in the rate of growth. 

 I am inclined to think, however, that the range of variation (6 inches) 

 is too great for the difference due to the rate of growth under natural 

 conditions. The fact, also, that the difference in average size at first 

 maturity of the southern and northern North Sea plaice is approxi- 

 mately equal to one year's growth speaks in favour of the same 

 conclusion." ***** 



The average size at which each sex matures for the first time being 

 that at which 50 per cent, become mature, it may be concluded from 

 these data that the average size for the females is 31-5 cm. ( = 12-5 inches), 

 and for the males about 25 cm. ( = 10 inches). Dr. Kyle concludes : — 

 " These values are a little less than those for the plaice of the southern 

 parts of the North Sea. If we assume that the numbers of the males 

 and females are approximately equal, then 28 cm. (11 inches) represents 

 the average size at which all plaice of both sexes become mature for 

 the first time." 



Section IV. 

 General Summary and Conclusions. 



By 

 Walter Garstang, M.A., F.Z.S. 



The facts and experiments recorded in the preceding sections lead to 

 the following main conclusions : — 



(1) Plaice below 8 inches in length are practically confined to the in- 

 shore waters of the bays at all seasons of the year. They are especially 

 abundant in Teignmouth Bay and Torbay, where they are caught with 

 the usual trawl-mesh in numbers at least as great as those of all the 

 larger sizes of plaice taken together. In Start Bay, on the other hand, 

 these small plaice are far less numerous than the larger fish, which out- 

 number them by eighteen to one (Table II., p. 449). 



In correlation with these facts the average size of all the plaice 

 caught during 1901-2 was found to be 12*8 inches for Start Bay, 

 7-8 inches for Torbay, and 7-9 inches for Teignmouth Bay. 



The actual percentages of small plaice caught in the bays were — 

 Teignmouth Bay, 60 per cent, ; Torbay, 50 per cent. ; Start Bay, 4 per 

 cent. 



* Twentieth Ann. Rep. S. F. B., iii. p 359. 



