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was the major cause affecting the western bluefin tuna stock for the following decades. But even this possibility
was never seriously analysed.

Even the presence of bluefin tuna (and consequent catches) in the North Atlantic up to Iceland is not clear from a
behavioural point of view, but if we consider the disappearance of this species in the North Sea and the strong
reduction of fishing yields in the southwest Atlantic as a sign of a reduction in the distribution area, then we
should consider the presence of bluefin tuna in the North Atlantic as an extension of the distribution area. But
this is only one of the human approaches, because bluefin tuna are not aware of this thinking.

There is another issue, which is possibly linked to the same area but it is very often forgotten by most of the
scientists working on bluefin tuna research. It was pointed out in the past several times mostly by Jones (1971),
Rodiguez Roda (1980), Cort (1980), Arena & Cefali (1982) and Arena (1982c, 1988). Some specimens were
found during the fishing activity in Norway (Rodiguez Roda (1980), while others were noticed in the Canary
Islands (Cort, 1980); Rivas (in Arena, 1980) reported that many specimens with bite marks are commonly found
among the bluefin tuna catches in the Bahamas. Bluefin tunas with these marks were reported also by Heldt
(1932) in Spain and Morocco, but the marks were wrongly attributed to the Risso’s dolphin (Grampus griseus).
In the Mediterranean, since the 1970s, several specimens of medium and large size bluefin tunas were found
with crater wounds in the lower posterior section of the body, in the perianal part (Figure 10).

These types of marks are typically caused by the bites of a small shark, Isistius brasiliensis (Quoy and Gaimard,
1824), the smalltooth cookiecutter shark. This shark species is distributed in several areas in various oceans, but
its presence is more common in the South Atlantic; it is not present in the Mediterranean Sea. It is usually a
deep-water shark (diving down to 3500 m), but having nocturnal movements up to the surface. The bites of
Isistius brasiliensis leave natural marks able to be distinguished and identified for the entire life of the fish. The
percentage of bluefin tuna with these marks in the catches from the South Tyrrhenian Sea varied from a
minimum of 0.68% to a maximum of 2% in the 1970s and the 1980s (Arena, 1982c, 1988a, 1988b, 1990; Arena
& Cefali, 1982); almost all these specimens were large males. Actually, according to the observers’ reports, the
presence of tuna with these natural marks is still reported every year in the central Mediterranean.

These interesting and curious natural marks pose various problems in our understanding of the bluefin tuna
movements and those questions remain unsolved even after the various tagging activities with pop-up satellite
tags and archival tags carried out in the 1990s and in recent years (Cort, 1999). As a matter of fact, only one
tagged bluefin tuna went from the Mediterranean to south of Cape Verde Islands. It is very difficult to
understand in which part of the Atlantic Ocean these marks are caused, but it seems logical that these natural
marks reveal movements which are not known by the scientists and a possible different distribution (maybe
vertical?) of medium and large males in some parts on the Atlantic Ocean, before migrating to the Mediterranean
for spawning.

There is another important issue, which is often forgotten when dealing with the eastern Atlantic stock of bluefin
tuna. It is well known since the time of Plinius (1st century B.C.), that an undefined portion of the Atlantic
bluefin tuna adult population remained in the Mediterranean Sea for an undefined number of years (more than
one year), wintering there. This point was raised many times in the 20th century (Genovese 1965; Scordia,
1934b, 1934c, 1935a) or even more recently (Di Natale et al., 2005c, 2005d) and this part of the stock is
certainly present in the deep central Mediterranean waters (including the area of the Strait of Messina) and it
should be possibly present also in the eastern Mediterranean (Karakulak and O ray, 2009), where it is supposed
that a portion of the sub-population originally located in the Black Sea might stay. The effects of these “resident”
bluefin tunas on the VPA have never been analysed.

As it was explicitly mentioned in the external assessment of ICCAT carried out in 2008 (ICCAT, 2009), maybe
there are too many ICCAT scientists knowing very well the mathematical models while only a few scientists
seem to really known the species and their life in the wild, often with an unbalanced situation. This fact is
creating a sort of parallel vision of what is happening in the reality, relying much more on numerical data
independently from their real meaning against the evidence coming from the situation at sea, where not
everything can be immediately translated into numbers.

5. The stock assessment

SCRS carried out several stock assessments of bluefin tuna and all of them were based on the huge database kept
by the ICCAT Secretariat, which includes the data transmitted by the Statistical Correspondents of each

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