Page 21 - Sella_M_1929

The habitat of the tuna appears to be regulated in large part by
the Gulf Stream ; in fact this coincides (even in the United States and"
Canada, where the tuna is lacking in the part subject to the cold Labrador
current), with the area in which the current of the Gulf makes its
influence felt. Evidently the presence of tuna north of Norway, at
the polar limits, can only be explained thus.

We can, to a certain extent, evaluate even the speed at which the
tuna are capable of dispersing, and can find confirmation that the fish
possess physical powers which render them able to make these great
seasonal wanderings, in the following fact. At Cristiansund in Norway,
where the arrival of the tuna is now checked by capable fishermen and
observers, the first tuna arrive in the first week of July, exceptionally
at the end of June. I have information from private sources to the
effect that Mr., Hanson caught a tuna which still showed traces of recent
spawning.,

These tuna certainly come from the southern zones of reproduction,"
of which the nearest is in Spanish waters or, in any case, not appreciably
farther north. The tuna never spawns before June. One can , then ,
calculate that in less than one month the tu na makes a journey , certainly
not direct , from the south of Spain to Norway^

Interesting, too, is the observation of Hanson (Cfro HHeg, in II
no 8, 1927, Milano), that in Norway regularly the
Risveglio della Pesca ,
large tuna appear first and then the small ones, with a lag of about 3
weekSo I consider this to be precisely in accord with the fact which I
have 'ascertained in the Italian and Tripolitanian fisheries, that the
large tuna ( around 100 kg or more ) matu re and release their sexual
products before the small tuna (15-30-50 kg); and actually the spawning
of the large tuna is finished at the beginning of July, while that of
the small tuna continues to the end of that month or a little longer,
in the fishery for returning tunao Also the disagreement noted above
between the classical spawning season of the tuna (May-June) and the
period in which actually the greater part of the tuna move off from the
northern coasts of the Mediterranean (June-July) results from this fact.

Among the direct proofs, then, of the movement of tuna from north
to south for reproductive purposes in the Mediterranean, it seems to me
that the most suggestive is that of the four leads from Constantinople,
found in a single fishing season (1927) and in different individuals,
in tuna from the fishery of El Mongar near Bengazi in Cyrenaica, which
cannot be explained except by the arrival en masse in Cyrenaica of
individuals coming from the Sea of Marmara and the BosphoruSo

Proposal to the Congress

l) For the study of the migrations of the tuna, I propose that in
agreement with our Spanish colleagues provisions be made for the marking
of a_ certain number of hooks of the Spanish type for fishing for tuna and

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