712 DEPTHS OF THE OCEAN 



a homogeneous composition. Their approach is heralded by 

 an immense swarm of Lepas fascicular is, which at the beginning 

 of May and June float passively on the surface of the northern 

 portion of the North Sea. Arachnactis albida follows soon 

 afterwards, as does also Physophora borealis. The salpse and 

 doliolids, which with Cipitlita sarsi, constitute the bulk, 

 generally make themselves visible in July, August, and 

 September." 



We know that these warm surface forms approach the coast 

 of western Norway, and as far north, for instance, as the 

 Trondhjem fjord.^ Even within the Norwegian Sea such 

 seasonal migrations occur, the warm water layers from the 

 eastern part spreading out over the deeper areas during summer. 



The foregoing remarks refer only to the passive migrations 

 or drift of pelagic forms with the currents of the sea. Fisher- 

 men have, however, long recognised the vast active migrations 

 of the powerful swimmers, especially fishes, generally supposed 

 to be undertaken in order to reach definite localities. The 

 first to submit these migrations to scientific investigation 

 was probably G. O. Sars. As to the herring fisheries on 

 the coasts of Norway he was struck with the fact that 

 while herrings of all sizes are captured along the entire 

 coast from the Skagerrack to the Barents Sea, spawning 

 herrings are only caught in large quantities on a definite 

 restricted portion of the coast, viz., from Stavanger to Romsdal 

 (the Norwegian North-Sea coast), and he concluded that the 

 herrings must necessarily migrate to these places to spawn, 

 enormous spawning-migrations entering as a necessary link in 

 the life-history of the herring. 



Numerous instances of such migrations are known from the 

 fishing industries, on the coast of Norway principally in the case 

 of herring and cod, and in Iceland of cod and plaice. I refer 

 the reader to my description of the migrations of the capelan 

 (Ma/lotics villosus) In the Finmark Sea^ (Barents Sea). This 

 small boreo-arctic fish spawns in spring on the coast banks of 

 Finmark, and during summer it migrates far north into the 

 Barents Sea towards the Ice-limit. In March 1901, when many 

 miles off the Finmark coast and over deep water, I could observe 

 and fish the capelan, the shoals being followed by millions of 

 auks, fulmars, kittlwakes, and gulls, the stomachs of which 

 contained capelan. 



^ See Nordgaard, loc. cit. 

 ' \l]ox{, Fiskeri og Hvalfatigsi i det iiordlige Norge, Bergen, 1902. 



