254 ruYsicAL and biological conditions in the north sea. 



in the warmer parts of the Atlantic far from the coasts. The warm 

 surface drift of the Gulf Stream carries them occasionally to the south- 

 west coast of Norway, as also to the west coasts of the British Islands, 

 but they do not penetrate through the English Channel and are, there- 

 fore, not seen in the southern part of the North Sea. They appear to 

 be usually taken on the Norwegian coast in summer. 



Certain deep-sea species extend from the Mediterranean to the coast 

 of Norway, such as Argentina sphyraena, but most of these have a very 

 wide range, and need not be considered in relation to the present 

 subject. 



The southern character of the fish found on the south-west coast of 

 Norway is strikingly exhibited by the numerous species of Scomhridae, 

 Fercidac, Sjyaridae, and Lahridac, which are found there. Besides those 

 which have been mentioned as occurring in the Western Baltic, we have 

 of shallow- water forms: — Pagdlus ccntrodontus ; Cantharus lineatus ; 

 Foli/prion ccrniuni ; Acantholdbnis cxoldus ; Acantliolabrus couchii ; 

 Pristiurus melanostomus ; Spinax niger (deep sea) ; Lamna cornubica : 

 NcropMs lumbriciformis. 



In considering the relation of the occurrence of these southern forms 

 on the south-west coast of Norway to physical conditions, we have to 

 remember that a narrow channel over 200 fathoms in depth runs along 

 that coast at no great distance from the shore, and that even the 100 

 fathom line does not go further north than the latitude of the north 

 coast of Scotland. The warm Gulf Stream is only a surface layer, and 

 beneath it is colder water. A large number of the southern species 

 have only been occasionally taken on the Norwegian coast, and then 

 chiefly in summer and autumn. They are probably to be regarded as 

 isolated stragglers, which have been partly tempted onwards by the 

 warmth of the water, partly carried by the surface drift. ]\'Iore 

 detailed information concerning the permanence or periodicity of the 

 occurrence of these species on this coast is required. The information 

 available in Smith's recent edition of Fries and Ekstrom's Scandinavian 

 Fishes, I have not yet had time to study thoroughly, as it is only given 

 in separate statements under each species. It would appear, however, 

 that a considerable number of littoral southern species are resident all 

 the year, and it is to be noted that the surface temperature on the 

 coast of Norway, to the north of 60° N. L., does not fall in February 

 below G°, while in the Heligoland Bight it is between 4° and 5° C. in 

 that month. 



It has been shown by the physical observations previously reviewed 

 that in summer a strong surface outflow from the Baltic northwards 

 along the Norwegian coast takes place, while in winter this is entirely 

 cut off. This water flowing out in summer is at a high temperature, 



