Page 20 - Sella_M_1929

) ) )
o

If J then, the tuna which inhabit all of the immense area described
above belong to the same race, the reproductive act, which is that which
determines the physiological reactions most typical of the species, will
take place in identical conditions, with the movement of the tuna to
We do not know all of these areas ^ and I
the same spawning grounds o
believe that there is much to be discovered in this fields but we have
no indication of their existence outside of the Mediterranean (and even
of a part of that sea) and outside of a limited part of the Atlantic
bordering on Spaino

Taking into account the results of the fishery in the North Sea^
we can schematize the movements of the adult tuna as follows (Fig„ 2)|

a In May-June groups of tuna are within the restricted area of
spawning situated toward the southern limit ( Mediterranean , Spanish
waters jT In this period the tuna are absent from the northern seas
and even (although not completely so) from the northern coasts of the
Mediterranean, with secondary differences of time due to differences
of habit between the small and large tunao

b Successive movements which are centrifugal ^ or more exactly,
which are directed essentially toward the north, with dispersion of the
tuna throughout all of the vast area of their habitats The majcimum
geographical diffusion takes place in the hottest months of summer -
autumn, and especially in September , at least in the Mediterraneano
The first tuna appear in the Horth Sea at the beginning of Julyo

c A new reduction of the habitat with the coming of wintero We
have little information on the extent of the winter habitat of the tuna,
because this is accompanied by a certain shift to deeper levels, but
it probably undergoes a notable reduction and in any case, in the north
and in the Atlantic, a displacement, because the tuna disappear com-
pletely from the North Sea after November or a little later On the
coasts of the northern Mediterranean all of the large tuna and almost
all of the sBiall ones move offshoroo

d) _In the period Mkrch-April, immediately preceding the
spawning season , the tuna meike a_ new migration, but much more
limited thaji that of the summer and autumn , toward the northo The
tuna reappear en masse on the north coasts of the Mediterranean, and in
the Atlantic we find them again on the Spanish coast of the Gulf of
Gasconys I do not believe that tuna have been sighted farther to the
north at this season.

Then there is a new concentration in May and June and a new
dispersal from the zones to the northo The small tuna absent them-
selves a little later, that is in June or Julyo

There take place, then, two movements of disp ersion, the first after
wintering , the second , much more extended, after sj

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