218 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



Cladocera, Chaetognatha, Euphausiacea, Mysidacea, Amphipoda and the 

 eggs and larvae of different invertebrates and fish. Herring feeds also on 

 fry, mainly its own. Its food varies greatly with the season (Fig. 92). The White 

 Sea herring fattens up in May : during the rest of the year its feeding is not 

 intensive. From September onwards herring practically stops eating, and the 

 percentage of empty stomachs in October may reach 40. In the spring its main 

 food is Calanus finmarchicus, in summer and autumn other Copepoda. 

 Spawning herring do not stop eating, but eat less. The rapacity of herring is 

 demonstrated not only by the fact that it prefers to devour great numbers of 



PORVYA INLET 

 MAY 



304 



PORVYA INLET 



JUNE 

 216 



NISHCHEVA 



INLET 



JULY 



99 



Fig. 92. Food ranges of the White Sea herring in different months 

 (Chayanova, 1939). Repletion indices denoted by associated 

 numerals. 1 Calanus finmarchicus; 2 Small Crustacea; 3 Euphau- 

 siaceae; 4 Mysidacea; 5 Amphipoda; 6 Sagitta; 7 Pteropoda; 

 8 Fish larvae. 



its own young, but also by its obvious preference for the larger forms of 

 plankton. 



The young navaga, like herring, feeds mostly on different small plankton 

 crustaceans. The food of the adult navaga is also greatly varied ; however, 

 contrary to that of the herring, its main food consists of benthos, chiefly worms 

 and crustaceans (up to 70 per cent of its food). One-fifth of navaga's food 

 consists of fish-smelt, caplin, launce, Boreogadus saida and others, including 

 navaga itself. Navaga grows more rapacious with age, often swallowing a 

 prey almost as big as itself. 



While spawning in January, navaga eats very little ; once its spawning is 

 over it once more falls greedily upon its food. 



Seals and porpoises are the navaga's chief enemies. 



Pollack or Polar cod also form an essential link in the food-chain of the 

 White Sea. The Arctic seas conceal an inexhaustible store of the small Gadidae. 



The young Polar cod, like navaga, feeds on crustaceans ; when growing in 

 size it changes to fish, and its predatory instincts and voracity are just as bad 

 as those of navaga, enormous numbers of which it devours, and for which it 

 itself also serves as food. The Greenland Sea, Phoca hispida and Delphinapterus 

 leucas devour countless masses of Polar cod, navaga and herring. 



