312 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Hensen calculates that the number of cod and plaice 

 annually caught by the Eckenforde fishermen 

 would, if allowed to remain in the sea, have produced 

 23,400 million cod and 73,895 million plaice eggs 

 annually. These figures are calculated from a nine-year 

 average. These numbers give for every square metre of 

 the 16 square miles of sea fished over 26' 6 cod and 84 

 plaice eggs; total 110'6 eggs. This, added to the 370 

 calculated above, gives a total of 480' 6, which represents 

 the number of eggs that would have been produced from 

 all cod and plaice, captured and free, yearly for each 

 square metre surface water. As a consequence 

 110' 6/480' 6 = 1/4*4, gives the fraction of the total quantity 

 of adult cod and plaice actually captured, or in other 

 words, man captures for his own use every year about 

 one-fourth of the total number of adult fish in this 

 particular area of the West Baltic. This result is 

 surprising to those who consider the resources of the sea 

 as inexhaustible, and believe that the number of fish 

 caught by man bears only a small proportion to the 

 number actually present in the sea. 



The estimation of the number of floating eggs accord- 

 ing to this method has important practical bearings. For 

 instance, it is possible to compare the fertility of a given 

 area of the sea with this area of the West Baltic, and so 

 to obtain an idea of the probable yearly catch of fish for 

 that area. The results in the North Sea invariably gave 

 a greater number of eggs per square centimetre than for 

 the Baltic. On the other hand, results in the open ocean 

 invariably gave less results than the Baltic. 



As an exceptional instance, Hensen found on the 20th 

 July, 1885, in the Skaggerrack 5,069 floating eggs per 

 square metre of surface water ; that is, for each square 

 mile of surface water 278,795 million eggs. On this same 



