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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

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