200 BRITISH FISHERIES 



able extent on the nature of the weather during 

 the preceding winter. We know, too, that the 

 incubation period of fish eggs depends closely on 

 the temperature of the water in which they are 

 developing. Thus, a flounder egg will hatch in 

 from five to ten days, the incubation period vary- 

 ing with the temperature. Plankton studies show 

 that the appearance and nature of microscopic life 

 in the sea depend on the weather. Diatoms are 

 more abundant during a temperate spring, when 

 there is plenty of sunlight. It is well known that 

 fishes are closely affected by the temperature of the 

 water : soles seek deep channels in cold weather, 

 and plaice may bury themselves in the sand in 

 such circumstances. It has even been shown that 

 there is an actual connection between temperature 

 and the abundance of anchovies in the Scheldt 

 fisheries. The catch of this fish varied in some 

 years according to the average temperature of the 

 water during the previous summer months. 1 

 There are other cases which might be quoted from 

 a study of the literature, all showing that the con- 

 nection between the abundance and movements 

 of sea-fishes and the physical conditions of the 

 medium in which they live is very close indeed. 



The earlier hydrographical research in Great 

 Britain was purely scientific in its aim. In the 

 famous voyage of the Challenger in 187276 an 



1 See Journal Mar. BioL Association, 1889-90, vol. i. (new 

 series), p. 340. 



