HJORT's studies of the NORWEGIAN FISHERIES. 57 



iu the Norwegian language in 1895, and in English in 1896. In the 

 present article I propose to give an account of Hjort's investigations, 

 since the main problems which they were designed to elucidate concern 

 the fisheries of the British Isles almost as closely as they concern the 

 fisheries of Norway. 



Hjort's enquiries may conveniently be described under three heads : 

 (1) Hydrography, (2) Plankton (floating fauna and flora), and (3) 

 Fisheries. 



These will be discussed iu the order mentioned. 



I. HYDROGRAPHy. 



Hjort's investigations were limited to the waters bathing the shores 

 of Norway from the Christiania fjord to the Lofoten Islands. The bulk 

 of his work, moreover, was deliberately confined to the region of the 

 West Coast Spring Herring Fishery, i.e., the immediate neighbourhood 

 of the mouth of the Hardanger fjord, in order that a complete know- 

 ledge might be obtained at this one spot of the periodical changes in 

 the character of the water throughout the year. 



His methods consisted in the analysis of a great number of samples 

 of water obtained in many localities at various depths, the temperature 

 of the dilferent samples having been registered at the time of collection. 

 He was successful in enlisting the interest and co-operation of a 

 number of navigating and fishery officers, and the Norwegian Govern- 

 ment placed a suitable steamship, H.N.M.S. Hcimdal, at his disposal. 



It will be remembered that Pettersson showed that the waters of 

 the Skagerack and Cattegat consist of two principal layers, having 

 different salinity and different temperature relations — a layer of light 

 water {i.e., of little salinity) on the surface, and a layer of dense water 

 below. These two principal layers are separated by an intermediate 

 layer of water, whose character, in regard to salinity and temperature, 

 is intermediate between those of the principal layers. 



The surface layer is Baltic water, the bottom layer is North Sea 

 water, and the intermediate layer, which crops up at the surface over 

 the shallow banks of Jutland and the west coast of Norway, is termed 

 by Pettersson "bank water" ("coast water" of Cunningham). 



The depth of the surface layer at different seasons depends on the 

 amount of fresh water liberated from the Baltic Sea, and ultimately 

 derived from tlie rivers which flow into it. This amount naturally 

 increases enormously in the spring and summer (April to September), 

 owing to rainfall and the thawing of ice and snow, and decreases 

 in autumn and winter (October to March), owing to the locking up 

 of the rivers by frost. 



