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al. (2003). It was clear that the composition of each tuna school was correlated to a very precise strategy of the
bluefin tuna, particularly during the spawning period. In these years, the shape and composition of the various
groups of bluefin tuna were deeply analysed and revealed complexities not known before. From Figure 7
(Arena, 1982a) it is clear that the strategy adopted by each school in the genetic period was able to affect the size
frequencies in catches, but this fact is never taken into account when catch are analysed or used in VPA. Not all
schools are the same in size composition, even in the same area.

The aerial observations were checked with landing controls, having a direct and scientific confirmation of the
size frequencies reported by the observers. The fishermen’s choice is an important component of this fishery,
together with the school composition and those factors combined are able to strongly interfere with our
understanding of the size composition of the stock. This is particularly relevant also because purse seine catches
represent more than 80% of the East bluefin tuna catch.

The effects of climate changes or oceanographic anomalies on Atlantic bluefin tuna behaviour, particularly on
mass movements, have been known for years (Bonhommeau et al., 2010 in press; Di Natale, 2007; Fromentin
2002b; Fromentin et al., 2000; Lemos & Gomes, 2004; Mackenzie & Myers, 2007; Ravier-Mailly, 2003; Ravier
& Fromentin, 2001, 2004; Roule, 1921), but the recent mass movements of this species have not been studied so
far, particularly in the Mediterranean Sea.

The tuna schools showed a different composition after the great change noticed around 1996, when the major
concentration of bluefin tuna moved away from the major spawning area in the southern Tyrrhenian Sea (Figure
8) going to the South Mediterranean and also to the East Mediterranean. This situation, possibly linked to
oceanographic factors (Di Natale, 2007), was partly reverted since 2006, when several groups of spawners
returned again to the South Tyrrhenian Sea. In the meantime, according to the catch composition concerning
purse seine catches moved into cages, the schools were more mixed, with a higher presence of new spawners
(fish around year classes 3 to 4). In the new situation, the typical shapes of the tuna schools in the spawning
period as studied by Arena (1982) became less defined, even if the “caravan” and “cone” shapes were among the
most frequent. But, even in these cases, the size distribution within the schools was more mixed and less defined.
Shortening the fishing period induced fishermen to maximize the yields and not to make any choice among the
schools depending on size composition.

Recent papers (Bonhommeau et al., in press; Fromentin et al., 2003; Sorell Baron, in press) confirm the
relevance of the aerial surveys, either for understanding the behaviour or to try to assess the presence and
abundance of bluefin tuna in various Mediterranean areas, even if there is very scarce attention to previous
literature on this subject. These fishery- independent estimates could possibly correct some problems in the
current assessments and all the available evidence shows that the presence of bluefin tuna at sea is considerably
higher than the model estimated.

There are more issues concerning the behaviour, the ethology and the migrations of tuna which are very relevant
for a more general overview of the bluefin tuna situation.

Furthermore, the problems are much more complex that they appear, because bluefin tuna have the bad habit of
not respecting the various hypothesis suggested by scientists. As a matter of fact, bluefin tuna had several non-
regular experiences in the past (Neuparth, 1925) and they are possibly having some more that we don’t know.

The idea to visit for several years the North Sea up to the Norway (Gruvel, 1922; Heldt, 1923, 1925, 1926; Le
Gall, 1926) was not so good. It seems that bluefin tuna were attracted in these cold and shallow waters mostly by
the high availability of good food with a high fat content (herrings and other species). Massive movements are
historically reported and the very rapid disappearance of this fishery (Tangen, 2009) (Figure 9, from 1950 to
1979) was mostly the reason for a dedicated Symposium by ICCAT held in 2008 (Anon. 2009). Therefore, it
seems that a combination of environmental factors, a decrease of the prey species due to overfishing and the high
fishing pressure applied to bluefin tuna in the short period were all together responsible for this disappearance
(Fromentin, 2002b; Fonteneau, 2009, Nøttestad et al, 2009). Even in this case, several people reacted, claiming
for a disaster for the bluefin tuna and some others tried to reiterate the same in recent times.

A similar situation, but with even more unclear displacement, occurred between 1951 and 1964 (Figure 9) in the
southwest Atlantic. This period was called “the Brazilian fishery” and it provided good yields for several years.
Then the massive presence of bluefin tuna decreased in a very short time and apparently most of the specimens
moved away from that area (Takeuchi et al., 2009). There are not many good scientific analyses or data about
the reason for these movements, but there is a good possibility that this intense fishery in the southwest Atlantic

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