In conclusion, if there is a passive or semi-passive movement of 

 young tuna through the Strait of Gibraltar, it should be remembered that 

 this occurs from the Atlantic to the Mediterranean^ in respect to the 

 position of the Iberian fisheries o 



lO) In a benevolent critique of my researches j Steuer (Into Revue 

 do geso Hydrob, Uo Hydrogr. , 1927) has pointed out the importance which 

 the nutritive plankton-bearing currents and their fluctuations might have 

 in determining the arrival of tuna from the Atlantic in the Mediterranean, 

 There is a tendency, in fact, to attribute a notable importance to the 

 migrations of planktonic forms from the Atlantic to the Mediterranean 

 (steuer, J3rgensenj Issel, and others)- 



But first of all it was necessary to ascertain whether the tuna 

 feeds on plankton, this fish being known only as an eater of fish and 

 large cephalopods. I will sximmarize the results of my researches on the 

 food habits of the tuna. 



In the tuna fisheries the stomachs of the tuna contain little foodj 

 in some cases perhaps the fish are often held in the traps for a length 

 of time sufficient for the digestion of the animals eaten before their 

 entrance. The tuna, however, feeds even during the period of maturation, 

 although with diminished activity. My observations confirm those of 

 De Buen in the Spanish tuna fisherieso 



For the examination of the nutrition of the tuna outside of the 

 spawning season I have preserved numerous stomachs of tuna caught in the 

 Strait of Messina at various seasons. Adding the results of these 

 examinations to the common knowledge of the fishermeni, it is possible to 

 say that the tunas 



a) Is_ especially an eater , even a_ ravager ,, of the most important 

 schooling pelagic fishes of small sizes in the Mediterranean above all 

 the sardine, the anchovy, the Clupea aurita , the mackerel, the Trachurus, 

 and the Belone acus ; in the north the young herring, etc„ , and even of 

 some fishes of somewhat larger sizes like Auxis , Th, alalonga, and in the 

 north the Gadus (Hanson)« Thus the occasional capture of the tuna on 

 hooks in the North Sea and in some places in the Mediterranean is subordi- 

 nate to the fishery for the species which are eaten (sardine, anchovy, 

 mackerel, herring). Only in a few places has it the importance of a 

 special fishery (Constantinople, the Canary Is„, Madeira, the Azores, 

 Messina, Arzeu, Tarifa, San Sebastian, Cristiansund)o 



The tuna feeds also on I'ishes which are coastal or rarely migratory 

 like the salpa ( Box ), various murenoids including the eel, etc. , and in 

 addition on large cephalopods like Loligo and Sepia, 



b) Is also an eater of true macroplankton , in particular of 

 heteropods ( Pteritrachea „ Carinaria )^ pvrosomas and salpas, and of decapod 



10 



