6o BRITISH SEA-FISHERIES 



mature individuals of a natural stock may be reduced 

 by man to a lower point which represents the eco- 

 nomic optimum. The Patagonian cannibals seem to 

 have been early converts to the soundness of this 

 theory. The difference between the Patagonian who 

 eats his mother-in-law and the fisherman who destroys 

 the overgrown plaice is that the former's actions are 

 deliberate and limited, while the removal of the accu- 

 mulated stock is not so much an object of the fisher- 

 man as an unpremeditated consequence of the intensity 

 with which fishing operations tend to be conducted. 

 Does the fisherman abate his operations when the 

 economic optimum has been reached ? Clearly not. 

 He fishes till it ceases to pay ; and no other motive 

 affects him. It is plainly a question for scientific 

 inquiry whether, in a given case, the fishery has been 

 prosecuted to excess, and has reduced the average age 

 too far, or not. 



On this question the International North Sea In- 

 vestigations have already thrown valuable light, for 

 the study of the intensity of fishing by means of 

 definite experiments with marked fish has formed an 

 important part of the programme ; and the investiga- 

 tion of the age of plaice, cod, and other species has 

 been vigorously prosecuted. According to the latest 

 report of the Council of the Marine Biological Associa- 

 tion, more than 7,000 marked plaice have been set free 

 by their staff, and 24 per cent, altogether have been 

 recaptured. Of the medium-sized fish which, furnish 

 the best test of the intensity of fishing, 30 per cent, in 

 twelve months have been captured in the southern 

 part of the North Sea, where sailing trawlers pre- 

 dominate, and 40 per cent, on the Dogger Bank and 

 adjacent grounds, where the fishing is done by steam- 

 trawlers. It seems, however, that some of the fish 

 lose their labels before being caught again. A still 

 closer idea of the severity of the fishing may perhaps 



