METABOLISM IN THE SEA 189 



fishes. The importance of this result is at 

 once apparent, for, since it is easy to calculate 

 the average number of eggs spawned annually 

 by each species of fish, it becomes possible to 

 estimate, within certain limits of error, the absolute 

 number of mature food-fishes inhabiting the fishing 

 grounds of the North Sea. By no other method 

 known to us is this possible. A similar investiga- 

 tion of a portion of the West Baltic (the Ecken- 

 forde fishing area) gave most interesting results. 

 It was estimated, from quantitative plankton fishing 

 experiments, that during the four months, January 

 to April 1885, there were spawned in all 370 

 eggs of cod and plaice per square metre of surface. 

 Now, the numbers of cod and plaice captured 

 during the same four months by the Eckenforde 

 fishermen was also known (being calculated from 

 a nine-year average), and knowing how many 

 eggs may be produced from a mature cod or 

 plaice, it is easy to calculate the number of eggs 

 those fishes would have produced if they had 

 been left in the sea. The result was 1 1 o eggs 

 per square metre. That is, all the cod and plaice, 

 captured and free, on this fishing ground would 

 have produced 480 eggs per square metre. But 

 men captured (in the shape of the parent fishes) 

 1 1 o eggs per square metre. Therefore in each 

 year the Eckenforde fishermen captured one- 

 fourth of the total number of adult plaice and 

 cod present in their fishing grounds, a result 



