550 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



surface for January, 45 to 50 for February, 00 for March, 

 and 50 for April. The average depth of water is given as 

 20 metres, and the eggs take 15 days on the average, 

 under the conditions prevailing in the Baltic, to develop, 

 so that the above numbers must be doubled to give the 

 number of eggs present per month under a square metre 

 of surface water. This gives 370 eggs per squnre metre 

 for the period January to April. From the returns of 

 the Eckenforde fishermen, it was calculated that the cod 

 and plaice annually caught would have produced 23,400 

 million cod and 73,895 million plaice eggs annually, if 

 left in the sea. 



These figures gave for every square metre of the 

 1G square miles over 26' 6 cod and 84 plaice eggs, a total 

 of 110*6 eggs, which represented the loss through the fish 

 being caught. If this is added to the number 370 above 

 calculated, the total 480*6 is the number of eggs produced 

 by all the cod and plaice, captured and free, yearly for 

 every square metre of surface water. The relation 110*6 : 

 480*6 = 1: 4*4, and this is described as giving the ratio 

 of the adult fish caught annually to the total number 

 present in this area — a capture of a quarter of the total 

 fish. 



This argument is, however, incorrect for the follow- 

 ing reasons. The number 110*6 represents the number of 

 eggs under each square metre of the surface, assuming 

 that all the eggs had survived which the fish caught 

 annually w T ere capable of producing in their ovaries. The 

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

 plaice eggs w T ere arrived at from direct estimations of the 

 number of eggs in the mature fishes. Now, it is well 

 known that the cod and plaice produce a very large number 

 of eggs, but that out of the enormous number only a 

 certain proportion survive. Hence the need for such a 



