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Furthermore, the level of noise had incredibly increased, at first at the end of the 20th century, when engines were
largely introduced in merchant marine and military vessels, and after the 2nd World War when engines were also
commonly adopted by fishing vessels and leisure boats. It is difficult to specifically attribute values to each
single location, but there are several scientific evidences about the impact of anthropogenic activities on some
tuna traps (Addis et al., 2009; Di Gregori & Massoli-Novelli, 1992; Grassi, 1913; Mazzarelli, 1917).

This resulted in a decreasing availability of the bluefin tuna in various areas independent from the total
abundance of the stock. It is clear that bluefin tuna moved from coastal waters to more offshore waters (cleaner
and quieter) in several areas, but they continued to pass along the historic migration courses in some areas. These
facts will provide a different key to read the yields history in this fishing activity and possibly even in others.

The second point is one of the less considered when discussing the Mediterranean populations of bluefin tuna
within the larger East Atlantic stock: the issue of the Black Sea bluefin tuna sub-population. Since historical
times there are many evidences of massive movements of bluefin tuna from the Black Sea to the East
Mediterranean for spawning (Figure 5) and then again back to the Black Sea for wintering.

This sub-population was there for many centuries until the second part of the 20th century, when it suddenly
almost disappeared. Zaitsev and Mamaiev (1997) and Kideys (2004) show how fast the decrease of the
population occurred, until the disappearance of any catch of bluefin tuna in the Black Sea waters of Bulgaria
around 1971 (Figure 6). Karakulak and Oray (2009) show how purse seine catches moved from the area in the
Black Sea close to the Bosphorus to the eastern Mediterranean in the last decades.

The bluefin tuna finally disappeared completely from the Black Sea, even from Turkish waters close to the
Bosphorus, in 19883.

Even in this case, besides the opinion by Daskalov (2003), it seems that the abundance in the Black Sea area was
not related to a direct fishery, but was affected by several collapses in the Black Sea environment (partly related
to fishery issues), which apparently forced the remaining bluefin tuna population to move into the Mediterranean
Sea. There are no scientific studies about the further distribution of this sub-population in the Mediterranean, but
it is strongly suspected that these tunas remained mostly in the eastern part of the basin, because of their natural
history tradition and the quality of the water there. This fact can be part of the reason why the Turkish fishery
obtained such good results in the last part of the 20th century and why genetic studies reveal a difference between
east and west tuna subpopulations in the Mediterranean Sea (Carp, 1951; Devedjian, 1926, Iyigungor, 1957;
Karakulak, 1999, 2000, 2003; Karakulak & Oray, 2009; Kideys, 2004; Merty et al., 2000; Oray et al., 2005;
Piccinetti et al., 1995; Piccinetti-Manfrin et al., 1995; Sarà, 1963; Tekin, 2000; Zaitsev, 2003; Zaitsev &
Manaiev, 1997). This was also the possible motivation for closing the Turkish tuna trap activities in the Strait of
Bosphorus. Again, even in this case, it is clear that bluefin tuna abundance in the various areas was mostly
affected by environmental and behavioural factors other than direct fishery ones.

4. The behavioural aspects

Bluefin tuna is a well developed species and a marine top predator. The behaviour is a very important and
essential component of its life, even if we know only a few aspects of bluefin tuna behaviour.

Ancient papers provided much information about the apparent behaviour of this species, while several papers in
the 17th, 18th and 19th centuries improved our knowledge, because scientists were spending a lot of time at sea, or
in fishing areas, or collecting direct information from the fishermen. Only in the last part of the 20th century, by
using more modern technologies, it was possible to better study some behavioural and ethological aspects of
bluefin tuna, particularly in the Mediterranean Sea (Bridges at al., 2009; Block et al., 2001, 2005; De Metrio,
2004, 2005; De Metrio et al., 2001, 2003), even if several problems are still existing (Fromentin, 2002b).

Thanks to the experience obtained from the use of aerial spotting to better catch bluefin tuna with modern
Mediterranean purse seiners4, the distribution and composition of the various schools of bluefin tuna were
studied by aerial observations by Farrugio (1979), Arena (1980, 1981, 1982a, 1982b, 1982c) and Fromentin et

3 In recent times, with the partial improvement of the environmental situation in the Black Sea, bluefin tuna are slowly reappearing in that
basin. In 2007, in late November, a few specimens were caught in the Marmara Sea and in the nearest areas of the Black Sea. In the same
period, juveniles having a size (about 700 g) much smaller than the usual size at that time of the year were found on the market in Istanbul,
providing evidence of possible reproduction in areas having a temperature colder than in other Mediterranean areas.
4 Aerial spotting for fishing bluefin tuna has been banned in the Mediterranean since 2006.

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