CHAPTER XXXII 



THE SMALL GAME OF THE SEA 



The Importance of Temperature 



From p. 445 of The Depths of the Ocean is reproduced Helland- 

 Hansen's chart showing the distribution of temperature in the 

 North Atlantic at a depth of 55 fathoms (100 metres). Hjort 

 notices (p. 444) that the ' northern ' forms of fishes hke cod, 

 haddock, coalfish, whiting, plaice, lemon soles, ling, and halibut, 

 which are taken mainly in the North Sea or in waters north of 

 the North Sea, are confined to an area north of the line which 

 marks a temperature of 50° F. at this depth. On both sides of 

 the Atlantic these northern forms live in water between 35° F. 

 and 50° F. at 55 fathoms, and ' the maximum frequency of the 

 species ' occurs between 42-8° F. and 46-4° F., but south of the 

 50° F. line, which touches the extreme north-wTst coast of 

 Ireland, and divides two areas known to marine naturalists 

 respectively as ' north-west ' and ' south-west of the British 

 Islands ', the northern fish do not occur (see map. Fig. 20). 



But the 50° F. line at 55 fathoms is not by any means the 

 northern frontier of the ' southern ' tribes. Hjort defines the 

 ' southern ' species as being fishes ' which are chiefly derived 

 from the Atlantic, notwithstanding the fact that little fishing 

 is carried on in this area ', and includes hake, soles, gurnards, 

 bream, monks, skate, and rays. From preceding chapters it 

 is clear that these tribes at certain times of year invade the 

 territory of the northern species. More especially in the 

 southern North Sea, on the grounds west of our islands, in the 

 Kattegat, and along the Skagerrak coast — where the summer 

 surface temperature of the sea runs high — but also in other 

 grounds like the Minch, ' southern ' and ' northern ' fish are 

 caught side by side. The wide range of the southern species is, 

 Hjort thinks, ' probably due to the fact that the water layers 

 in the North Atlantic run north.' Thus the southern species in 

 their youngest stages drift northwards, and ' may as a conse- 

 quence pass their youth very far from the localities where they 

 were born '. 



Hjort's investigations showed him that the southern com- 

 mercial fishes like hake did not occur below the 300-fathom 

 line. Hake, ling, and bream are trawled by commercial vessels 

 at 200 and 300 fathoms both off the w^est of Ireland and off 

 Morocco. They are caught, in fact, in the deepest waters which 



