172 A CENSUS OF THE SEA [PART II 



must be added the numbers of ripe male fishes, and the numbers 

 of immature fishes of both sexes. These quantities can be calcu- 

 lated from a knowledge of the ratios of females to males, and from 

 the ratio of mature to immature fishes of the six species dealt with. 

 The material for the construction of these ratios exists in the 

 fisheries literature. Fulton determined the ratios of the sexes in 

 the case of most edible fishes, and for the six species in question, 

 it is 



Females : males = 280 : 100. 



But it is much more difficult to estimate the ratio that mature 

 fishes bear to immature ones. A good deal of work has been done 

 in this direction but the results are not collated. In 1894 Holt^ 

 calculated that about 7,084,000 mature plaice were landed at 

 Grimsby during the period April 1893 — March 1894, and that 

 9,166,000 immature plaice were landed during the same twelve 

 months. Therefore more immature plaice are caught than mature 

 ones, and the same is true with regard to the other species. The 

 ratio varies with the season, the locality, and the method of fishing ; 

 thus the whole inshore plaice fishery is practically one for immature 

 :fish, and enormous numbers of the smaller fishes are landed at 

 some ports (London, for instance), while very large quantities are 

 sometimes caught by the trawlers and are not brought ashore at all. 

 Generally speaking the numbers of immature individuals of a 

 species are greatly in excess of the mature individuals. I think 

 that for the North Sea, and for the six fishes mentioned, we may 

 assume that the ratio of mature to immature individuals is about 

 1 : 5. This estimate may not be accurate but it cannot be very far 

 out. Considering then both the mature males, and the immature 

 fishes of both sexes our estimate of part of the fish population of 

 the North Sea in 1895 becomes : — 



Mature female cod, haddock, plaice, flounders, dabs 



and long rough dabs 1206,319,000 



Mature males of the same species 430,000,000 



Immature males and females of the same species ... 8180,000,000 



Total population... 9816,319,000 



^ Holt, Journal Marine Biol. Ass. Vol. iv. p. 414, 1895 — 7. 



