directly opposite to the usual "ar- 

 rival" pattern. 



The "return" situation is much 

 simpler. Tuna apparently swam 

 southward along the southern half of 

 the east coast of Sicily, and west- 

 ward along the western half of its 

 southern coast. 



The above discussion is obvi- 

 ously simplified, and is only intended 

 to show trends in the movements of 

 the tunas. There have been many 

 varying opinions on how the tuna 

 approach the coasts and enter the traps 

 (Scaccini and Pacagnella 1965), We 

 do not mean to imply that the entire 

 mass of fish in a given area follows 

 the route described, but only that 

 many fish in the respective areas tend 

 to travel in the stated directions. 



Most of the early theories on the 

 migrations were based mainly on in- 

 formation of the type which has been 

 summarized above. It should be 

 noted, however, that the European 

 fisheries have a very ancient history, 

 whereas most of those in Africa origi- 

 nated in modern times. 



The theories on migrations of 

 bluefin, developed largely from stud- 

 ies of the trap catches, and later from 

 consideration of environmental fac- 

 tors as well, varied from Aristotle's 

 (circa 325 B.C.) view that the bluefin 

 was an Atlantic species which occu- 

 pied the Mediterranean only on its 

 way to and from its supposed spawn- 

 ing grounds in the Black Sea, to the 

 concepts of Pavesi (1889), Sanzo 

 (1910a), Roule (1914a), F. de Buen 

 (1925), and Scordia (1938) that the 

 Mediterranean and Atlantic bluefin 

 constituted entirely separate popula- 

 tions. Pavesi (1889) thought that the 

 Mediterranean bluefin was an abys- 

 sal animal, rising from the depths of 

 that sea and moving to nearby sur- 

 face waters only to spawn. Bounhiol 

 (1911) shared in the concept of a 

 strictly Mediterranean bluefin stock 

 but believed that its apparent migra- 

 tions were actually the result of a 

 tendency to swim against the wind- 

 driven currents. Roule (1914a) felt 

 that the bluefin was a pelagic crea- 

 ture which migrated only within the 

 basin of the Mediterranean in which 

 it lived. He believed that its spawn- 

 ing migrations were controlled by the 

 temperature and salinity of the wa- 



ter. Scordia (1938) and others (Ninni 

 1922, Genovese 1957) thought that 

 there were two or more stocks of 

 bluefin within the Mediterranean, 

 each native to its particular basin. 

 Some authors even questioned 

 whether bluefin tuna actually oc- 

 curred in the Atlantic (except in the 

 Ibero Moroccan Bay) in significant 

 numbers, or whether the bluefin re- 

 ported from the Atlantic were of the 

 same species as those in the Mediter- 

 ranean. 



These theories were predom inant 

 in the late 1800s and early 1900s, 

 until Sella (1926a, 1926b, 1927, 

 1929a, 1929b, 1930, 1932a, 1932b) 

 hypothesized several migrations from 

 various Atlantic areas and from the 

 Sea of Marmara into the Mediterra- 

 nean, as well as between the differ- 

 ent basins of that sea. He deduced 

 these migrations by determining the 

 localities where hooks and lures 

 found in bluefin, which had broken 

 lines or leaders and subsequently been 

 caught in traps, were in general use. 

 In that period, tuna fishermen used 

 hooks and lures which were hand- 

 made locally. Distinctive designs and 

 methods of attachment to lines or 

 leaders made hooks and lures from 

 different localities easily recogniz- 

 able. Thus it might be assumed that a 

 fish found carrying a hook or lure 

 typical of a given area had come from 

 that area. In some cases, this prob- 

 ability was greatly increased by many 

 findings, indicating similar migra- 

 tions. This somewhat uncertain 

 method was followed by the more 

 positive ones of sonar tracking 

 (LozanoCabo 1959a, 1959b) and tag- 

 ging (Rodri'guez-Roda 1964c, 1969a; 

 Hamre 1965, Arena and Li Greci 

 1970, Aloncle 1972, Lambouef 

 1975). Studies of the effects of 

 environmental conditions on the oc- 

 currences and behavior of tunas, par- 

 ticularly during the spawning sea- 

 son, and analyses of the time, loca- 

 tion, quantity and size composition 

 of catches, continued to provide de- 

 ductive indications in regard to mi- 

 grations concurrently (J. Le Gall 

 l929,J.Y.Le Gall 1974. Hamre 1958, 

 1962, 1965; Lozano Cabo 1958, 

 Rodriguez-Roda 1963, 1964a, 1969b, 

 1970a, 1970b; Aloncle 1964, Arena 

 1964, Sara 1964. 1973;Tiews 1964). 



Numerous biometric compari- 

 sons of morphometric and meristic 

 characters of bluefin tuna from vari- 

 ous areas were carried out to identify 

 populations or races (Frade 1931, 

 Arico and Genovese 1953, Nedelec 

 1954, Genovese 1957, 1958). More 

 recently, some genetic and biochemi- 

 cal research has been undertaken for 

 the same purpose (Keyvanfar 1962, 

 Lee 1965, 1968). 



Despite all of these efforts, un- 

 certainties about the migration pat- 

 terns and the identity of the stocks in 

 the eastern Atlantic and the Mediter- 

 ranean still exist. 



b. Migrations Between the 

 Mediterranean and the 

 Eastern Atlantic 



Unit stock or two stocks? — The 

 question of whether the bluefin tuna 

 constitute a single stock which mi- 

 grates from the Atlantic into the 

 Mediterranean to spawn and then out 

 again, or comprise two stocks — one 

 Atlantic and one Mediterranean — 

 has been debated for decades. This 

 discussion led to such terms as the 

 "migratory" or "sedentary" tuna, (re- 

 ferring to the supposed habits of the 

 fish) and the "unitists" or "dualists" 

 (referring to the theories on the num- 

 ber of stocks). 



Ancient trap fisheries in the 

 Mediterranean Sea and its approaches 

 were based on the spawning runs of 

 the larger bluefin: an eastward "ar- 

 rival" run. mostly of fat fish with 

 ripening gonads, in May and June 

 and a westward "return" run, mostly 

 of lean spent fish, in July and Au- 

 gust. These runs were the basis of the 

 Aristotelian theory, that the bluefin 

 was essentially an Atlantic species, 

 but passed through the Mediterranean 

 in May and June to spawn in the 

 Black Sea, and returned to the Atlan- 

 tic in July and August. This theory 

 has been accepted, wholly or in part, 

 by nearly all of the trap fishermen to 

 this day, and also by many scientists. 

 Objectors (Pavesi 1887, 1889; 

 de Bragan^a 1899, Sanzo 1910a, 

 Roule 1914a, 1914b, 1917, 1924; F. 

 de Buen 1925, 1931; O. de Buen 

 1924, Scordia 1938) noted that blue- 

 fin spawned in the Mediterranean and 

 that individuals of all sizes were 

 present in it throughout the year. They 

 also maintained that the lag which 



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