central Mediterranean. This last find- 

 ing was criticized (Pavesi 1 887), but 

 recent evidence (SarA 1 973) indicates 

 that it was surprisingly accurate. 



Pavesi (1887, 1889), who was 

 the first to seriously challenge the 

 migratory theory, believed that the 

 Mediterranean (and eastern Atlantic) 

 bluefin spent most of the year in abys- 

 sal waters near their spawning 

 grounds. His theory restricted their 

 migrations to a vertical ascent to su- 

 perficial water and a short horizontal 

 migration to a nearby spawning 

 ground in spring, and short horizon- 

 tal return and a vertical descent into 

 tlie abyss after spawning. 



Sanzo (1910a) agreed with 

 Pavesi (1887) in regard to the com- 

 plete separation of the Atlantic and 

 Mediterranean bluefin stocks. He had 

 doubts, however, in regard to Pavesi's 

 hypothetical bathymetric migrations. 

 He recommended investigating the 

 darkness or lightness of the colora- 

 tion and other characteristics of the 

 tuna when they first arrived at the 

 traps to determine whether they had 

 come from the abyssal depths or from 

 the surface layers. He believed that 

 spawning was independent of the 

 coastal movements of the tuna, and 

 that other causes of their comings 

 and goings in the Mediterranean 

 should be sought. 



Bounhiol (1911a, 1911b) also 

 believed that the Mediterranean blue- 

 fin tuna stock was separate from that 

 of the Atlantic. He introduced a new 

 concept, however, that the bluefin in 

 the Mediterranean always moved 

 against the wind-driven surface cur- 

 rents — the "hydrodynamic" theory. 

 This theory has received scant sup- 

 port. 



Ninni (1922) discussed hypo- 

 thetical populations and migrations 

 of bluefin tuna in the Mediterranean 

 in considerable detail. He believed 

 that the Tyrrhenian bluefin were in- 

 dependent of the Adriatic ones and 

 that both were independent of those 

 of the Aegean Sea, and that the last 

 were at least partly independent of 

 those of the Sea of Marmara. Ninni 

 assumed each group had its own well 

 defined wintering area. He shared the 

 opinion of Pavesi (1887) that the 

 bluefin tuna wintered in deep waters. 



Ninni believed that the major 

 eastward migration of bluefin tuna 

 must have departed from the winter- 

 ing area between Sardinia and Tuni- 

 sia, passing along the northeastern 

 coast of Tunis then along or offshore 

 from the Tripolitanian coast toward 

 Bengasi. There Ninni's personal ob- 

 servations ended, but he felt that the 

 bluefin avoided the Nile outfiow and 

 turned toward Crete. Ninni thought 

 that there was a wintering area around 

 Crete, and possibly another between 

 Crete and Alexandria. Egypt. 



Ninni hypothesized that when the 

 fish left the Cretan wintering area 

 they split into two groups. The smaller 

 group went up the western Aegean, 

 passing between Euboea and the 

 mainland of Greece and entering the 

 Gulf of Volos. The larger group fol- 

 lowed the Asiatic coast to the 

 Dardanelles and into the Sea of 

 Marmara and the Bosphorus, always 

 leaving the islands on their left. They 

 passed through the Bosphorus and 

 "lost themselves" in the Black Sea. 

 The passage into the Black Sea be- 

 gan March 15 and lasted into Au- 

 gust, after which the "return" began, 

 but not all of the bluefin went back 

 into the Aegean. A large proportion 

 of them wintered in the Sea of 

 Marmara. Ninni's hypotheses do not 

 lead to an annually repeated migra- 

 tory cycle; in successive years the 

 same fish might winter once between 

 Sardinia and Tunisia, once near Crete, 

 and once in the Sea of Marmara. Such 

 shifts of habitat (or migratory pat- 

 tern) are unusual. 



Roule (1914a, 1914b. 1917, 

 1924) believed that the bluefin were 

 pelagic or bathypelagic rather than 

 abyssal, but he felt that their migra- 

 tions were restricted to the particular 

 basins of the Mediterranean which 

 they occupied. He (1924) studied 

 temperature and salinity observations 

 made during the season of spawning 

 assembly (May-June) in 1923 be- 

 tween southern France and Tunisia. 

 He found that the line of maximum 

 thermal increment ran directly from 

 southern France to Tunisia, fitting 

 his (1917) hypothesis that uhen the 

 bluefin were absent from the former 

 area, they were in the latter to spawn. 

 He found that these observations sup- 

 ported his halothermic theory in re- 



gard to water temperature, but 

 showed no correlation in regard to 

 salinity. 



Sella (1927) disputed Roule's 

 (1917, 1924, 1926) hypothesis that 

 the tuna which occurred off the south- 

 em coast of France during the re- 

 mainder of the year spawned in May 

 and June near the traps off Sardinia, 

 Sicily and Tunisia. He showed that 

 the tuna caught off the southern coast 

 of France averaged only about 20 kg, 

 whereas those caught in the traps av- 

 eraged from 70 kg to 130 kg. The 

 differences between Roule's and 

 Sella's opinions in regard to the sen- 

 sitivity of the bluefin to the tem- 

 perature and salinity of the water, 

 and the effects of these factors on its 

 distribution and migrations, have 

 been discussed in Section VE2. 



Scordia (1938) maintained that 

 the bluefin tuna which she studied 

 off eastern Sicily and the west coast 

 of Calabria (southern Italy) were of a 

 distinct and separate stock which she 

 called the Tyrrheno-lonian stock. She 

 observed that these tuna remained 

 mainly in the deep waters of the lower 

 (southern) Tyrrhenian in autumn and 

 winter, sometimes rising to the sur- 

 face near Messina in the fall to feed. 

 They surfaced in the spring with the 

 wanning of the waters to 18°C. When 

 increased warming reduced the den- 

 sity in siiii, from between 1.02700 

 and 1.02800 to about 1.02500, the 

 tuna moved from the Tyrrhenian 

 through the Strait of Messina into the 

 Ionian Sea, where the density was 

 higher. This occurred toward the end 

 of May and in the first half of June. 

 During June the continued warming 

 reduced the density in the Ionian Sea. 

 The tuna then returned to the deep 

 waters of the Tyrrhenian where the 

 density was suitable for them. They 

 went a few at a time, with the large 

 fish departing first, followed by 

 smaller ones up to September. These 

 movements, which constituted the 

 "arrival" and "return" runs, were 

 based on the sensitive reactions of 

 the fish. At the beginning of their 

 period of sexual maturity they un- 

 derwent a reversal of their thermo- 

 tactic reaction. During the winter they 

 chose a water temperature of about 

 13.5-I4.5^C. but with the approach 

 of the spawning period, they became 



105 



