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SCIENCE PROGRESS 



quantities of liver taken are hectolitres per thousand cod caught; 

 the quantities of roe are litres per thousand fish caught, and the 

 latter figures have been " smoothed " by application of the well- 

 known statistical formula, mean value of b = , such a 



4 



mean value being substituted for each of the original values. 

 It is at once seen that there is a direct relationship between 

 quantities of roe and liver taken, and the variations from the 

 mean of air-temperature. That is, the lower is the temperature 

 of the air, the higher is the quantity of those products obtained. 

 The correspondence is not particularly good, but it serves to 

 support the conclusion already drawn, that the more intense 



1880 



-t 



Fig. 8. — Productivity of the Lofoten cod-fishery compared with the air-temperature. 



Scale I. is "C; II. represents hectolitres of liver per thousand fishes caught ; III. litres of cod-roe per 

 thousand fishes caught ; and IV. relative numbers of sunspots. (From Helland-Hansen and Nansen, 

 loc. cit. p. 3 55.) 



the Gulf Stream flow, the lower is the state of nutrition of 

 the fish; for we have seen that the air-temperature varies directly 

 as the temperature of the surface water of the sea. 



The cod which reach the fishing-grounds at Lofoten are 

 almost all sexually mature fishes, and their age varies from 

 five to seven years. A certain proportion of these fishes have 

 no doubt already made the shoreward migration and have 

 spawned at least once before in their lives, but the majority 

 are probably fishes which are sexually mature for the first 

 time in their lives — that is, they represent the brood of some 

 one particular year. If this is so, we ought to be able to refer 

 them to some spawning-period about seven years prior to the 



