a comparison of the contents of herrings' stomachs with plankton collected at the same time show- 

 ed the composition of the plankton in the 0-50 m. layer to be extremely poor; the plankton con- 

 sisted of Ca^anus finmarchicus stage of maturity), Pseudocalanus elongatus , Qjthona 

 atlantica and young Gastropoda . 



All these organisms were represented in the catches in minute quantities, whereas the 

 principal diet of the herring in February consisted of adult Euphausiacea (mean 'fullness' index for 

 a feeding herring was 96.7 and 70.3). 



In March 1952 and 1954, the composition of the plankton in the fishing grounds was some- 

 what richer than in February. The principal organsims characterizing the plankton samples in 

 these years were the following: Calanus finmarchicus , stage V-VI - very little, Pseudocalanus 

 elongatus , Oithona similis , Oithona atlantica , Acartia clausi, young Gastropoda, eggs of Euphaus- 

 iacea, Oikopleura labradoriensis , etc. All these forms, with the exception of Calanus finmarch - 

 icus, were found only in occasional specimens in the samples . 



The food of the herring at the corresponding dates in 1952 consisted of 3% Calanus finmarch - 

 icus, 24% Themisto abyssorum and Themisto compressa f^ bispinosa , 52% adult Euphausiacea and 

 21% young wolf fish . Only adult forms of Euphausiacea were found in the stomachs in 1954 . 



The composition of the plankton on the fishing grounds was qualitatively identical in April 

 1952, 1953, and 1954. The plankton samples contained the following organisms: Calanus finmarch- 

 icus , Pseudocalanus elongatus , Oithona atlantica, Oithona similis, Oikopleura labradoriensis, 

 young Themisto abyssorum and Collozoum . 



The principal food of the herring during this month in all the years consisted of adult forms 

 of Euphausiacea (55%), Calanus finmarchicus (40%), Themisto abyssorum and Oikopleura labrador- 

 iensis . The food of the herring did not contain all the plankton forms found in the plankton samples; 

 at the same time, organisms not represented in the plankton samples were found in the stomachs. 



The number of different plankton forms present in all the plankton samples taken during the 

 spring and summer periods was much greater than the number of organisms used by the herring 

 for food. 



We can therefore conclude that the herring feeds on those organisms which populate the 

 water in its habitat, but that it actively selects the larger organisms instead of passively filtering 

 the water through its branchial apparatus . 



Of all the forms of plankton which populate the water, the herring selects two or three, 

 while the rest are of no importance to its food spectrum. Our findings show that in the winter- 

 spring period the most favored herring food is adult forms of Euphausiacea . During the spring- 

 summer months, the most frequently selected organisms were Calanus finmarchicus , Calanus 

 hyperboreus , Themisto sp., young Euphausiacea and Oikopleura ; in the summer-autumn period, 

 adult Eupiiausiacea again predominate in the food. 



Weight, Nutritional Condition, and Fatness of Herring 



in Dependence on Food 



The influence of the food on the weight increase of herring, their nutritional condition, 

 their fatness and the development of their gonads can be seen from the tables and Figure 6. 



156 



