8 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



workers undertake to solve by means of their system of 

 plankton observation. From a series of 120 observations 

 in the Eckenforde district of the West Baltic, Hensen 

 concluded that from January to April, over an area of 

 about 16 square miles, there are in all 3T0 eggs of cod 

 and flat fish per square metre of surface. He also 

 calculates that the fish caught in the same district would, 

 if left in the sea, produce 110" 6 eggs per square metre, 

 and the relation between these two totals shows that the 

 fishermen capture in that district about one-fourth of the 

 fish population annually. It is obvious that the correct- 

 ness of this conclusion depends entirely upon how far the 

 120 original observations were truly representative of the 

 16 square miles of sea fished. 



As the result of three series of 49, 50, and 59 catches 

 respectively, made in the North Sea in 1895, Hensen and 

 Apstein computed that the North Sea contained that 

 season, in its surface waters, 157 billions of fish eggs. 

 Here the quantity in the 547,623 million square metres 

 of the North Sea has been estimated from 158 sample- 

 catches, and from our knowledge of the average number of 

 eggs produced annually by each kind of fish, it is stated 

 that we can arrive at the actual number of mature food 

 fishes of the North Sea — a colossal conclusion to base 

 upon such a small number of samples as 158 — only one 

 for each 3,465,968,354 square metres of surface. 



From certain samples obtained from the West Baltic 

 it has been calculated that every square mile contains 80 

 to 100 billion Copepoda, and from the relative proportions 

 of eggs, larvae and adults it is deduced that for the 16 

 square miles of the fishery district the annual consumption 

 of Copepoda must be 15,600 billions; and that con- 

 sequently that district supports Copepod food sufficient for 

 534 million herring of average size. 



