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 

 the same spawning grounds o We do not know all of these areas ^ and I 

 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 o 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 



16 



