62 The Distribution of Parasite -Infected Fish 



deepest part of the channel is stated by Helland-Hansen to be covered 

 nearly always with water of a temperature below 32° F. This water is 

 an ofEshoot from the bottom water of the Norwegian 8ea. It has been 

 found that the bottom water runs nearer to the surface in the southern 

 than in the northern part. The depth of the Atlantic current may be 

 from 2 to 300 fathoms. Owin<j to the influence of the earth's rotation it 

 is, according to Petersson, bent to the east and it sends a branch round 

 Orkney and Shetland over the northern North Sea plateau into the 

 depths of the Norwegian channel as far as to the Skager Rak. The 

 trawl fishery is carried on in this water of Atlantic origin over the whole 

 northern North Sea plateau (deeper than 43 fathoms), as far as the 

 Dogger Bank, and over the western and southern slope of the Norwegian 

 channel (Great Fisher Bank, Jutland Bank, etc.). 



Whether the Atlantic current has any special influence with regard 

 to the parasite-infection of the fish is an obscure question, as is also the 

 question whether the fish caught at Shetland for example have been 

 born in some other region. Schmidt deals with the distribution of the 

 fry of the cod, haddock, etc. He says that the pelagic fry {i.e. the early 

 stages which have not yet taken up life on the bottom) of the cod pro- 

 duced on the coastal banks at Iceland cannot be carried away from that 

 island to other coasts by currents. It is said however that Iceland cod 

 occur among the fish caught at Faroe and landed at Aberdeen. It Avould 

 appear also that the fry do not leave the Faroe region to any important 

 extent, with the exception perhaps of some migration from the banks 

 south of the islands. The North and Norwegian Seas receive from the 

 Atlantic a large import of haddock, ling, etc. in the pelagic stage. 



Until more extended investigations are made, it may be tentatively 

 concluded that the infected haddocks and cod are restricted in their 

 distribution, and one w^ould be inclined therefore to look for the cause in 

 the local environmental factors, but the problem is a very wide and 

 intricate one. 



