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65). This area could act as a retention area with low current velocities. A second area of low
flow velocities is the southeast end of the Gulf of Gela, off Sicily, due to the detachment of
the AIS from the shore, as observed from the general circulation pattern.

Larval distribution shows the role played by advection. Larval abundance and larval size
increase towards the southeast (Fig. 65), and Cape Passero not only registers maximum
larval densities but also larger individuals. On the other hand, the locally unbalanced ratio
anchovy eggs/anchovy larvae in this zone indicates that the larvae did not hatch there, but
were advected from other areas.

High larval concentration observed by Garcia Lafuente et al. (2002) off Cape Passero raises
the question of whether there are physical reasons for defining it as a retention area. As
shown in Figure 14, the general surface circulation of the AIS generates vortices. These
result in the formation of a series of anticyclonic and cyclonic vortex off the southern coast of
Sicily and Malta. The maintenance of cyclonic vortex implies the existence of upwelling at its
centre to counterbalance the effects of friction. This is a suitable condition for sustaining high
rates of primary production. Convergence generated by anticyclonic eddies southeast of
Cape Passero allows the larvae to maintain their relative position in an area where retention
also provides favourable conditions for larval feeding and growth.

5.3 Bluefin tuna (Thunnus thynnus) spawning area

Tuna are known to spawn in SSTs above 24°C. In the Levantine Sea, SSTs values between
22.5 and 24.9 C are generally recorded from the second half of May, while in the eastern
Mediterranean, the reproductive season of bluefin tuna starts almost 1 month earlier (mid-
late May) than in other Mediterranean spawning grounds (June-early July). Several years of
investigation on bluefin tuna larvae distribution, as well as studies on the presence of
females with hydrated oocytes and post-ovulatory follicles, have not sufficed to complete the
map of spawning areas in the Mediterranean. Large knowledge gaps mainly exist for the
eastern basin, where an important spawning ground has been recently identified North of
Cyprus (Karakulak et al., 2004) (Fig. 53).

According to the results of larval campaigns, bluefin tuna spawn within a large portion of the
pelagic Mediterranean environment (Piccinetti et al., 1997; Nishida et al. 1997; Tsuji et al.,
1997). Remarkable concentration of eggs and larvae occurs south of the Balearic islands,
around Malta, off the eastern coast of Sicily and in the South Tyrrhenian Sea, where
hydrological features are more favourable for their survival (Charbonnier and Garcia, 1985)
(Fig. 54).

As shown by tagging campaigns (De Metrio et al., 2004), movement of T. thynnus within the
Mediterranean Sea is often limited, particularly for individuals tagged in the eastern regions

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