Figure 71. Geographic distribution of bluefin release and recapture 

 data shown in Table 27. 



Cabo has apparently provided first- 

 hand evidence against the existence 

 of the thermal or halothermic barrier 

 to maturing bluefin at the Strait pos- 

 tulated by Roule (1914a), F. de Buen 

 (1931) and others. 



The sizes of schools were also 

 difficult to determine. Lozano Cabo 

 estimated that one of the largest 

 schools, observed on June 21, 1957, 

 between Algeciras and Tarifa, Spain, 

 occupied about 7,200,000 m\ If the 

 fish were 20 m apart in all dimen- 

 sions, their number would have been 

 1,922. If the spacing were reduced to 

 10 m, the number would be 11,163. 



Lozano Cabo estimated the av- 

 erage speed of the schools at less 

 than 7 knots (13 km/hr). He pointed 

 out that, although the schools ob- 

 served in the Strait were numerous 

 and large, it should be recalled that 

 1957 was a very good tuna year. 



Some uncertainties may exist in 

 regard to the actual origin of Sella's 

 (1927, 1929a) hooks and the identity 

 of Lozano Cabo's (1959b) sonar tar- 

 gets, but Rodriguez-Roda (1963, 

 1964c, 1969a) provided indisputable 

 proof of bluefm tuna migrations from 



the Atlantic into the Mediterranean. 

 He marked 3 1 2 bluefin tuna, ranging 

 from 60 to 220 cm in length, from 

 catches in traps near Cadiz, Spain, in 

 1960-1968. Four of these fish were 

 recaptured in the Mediterranean and 

 15 in Atlantic waters off southern 

 Spain and Portugal and western Mo- 

 rocco (Table 27, Figure 71). 



The Mediterranean returns are 

 of special interest, in view of the 

 long debate as to whether or not im- 

 portant numbers of bluefin tuna mi- 

 grated through the Strait of Gibraltar. 

 Two of the fish were recaptured at 

 La Linea and Ceuta, Spanish ports 

 on the north and south sides of the 

 Mediterranean outlet of the Strait, 

 respectively, and about 40 nautical 

 miles (64 km) from the release point. 

 The other two, recaptured off 

 Cartagena, Spain, and Palavas, 

 France, had penetrated much more 

 deeply into the Mediterranean, 270 

 and 675 nautical miles (43 1 and 1 ,080 

 km) respectively, from the release 

 point. Three of the releases were in 

 May and June, during the "arrival" 

 run when the fish are supposed to be 

 travelling eastward. The fourth, how- 



ever, was during the "return" run, 

 when they are thought to be travel- 

 ling westward. The recaptures were 

 all in July or August, during the "re- 

 turn" run. Times at large varied from 

 19 to 23 days, and the weights (jf the 

 fish were 41, 83, 90 and 120 kg (me- 

 dium size range). These returns dem- 

 onstrate conclusively that some blue- 

 fin enter the Mediterranean from the 

 Atlantic. They also suggest that some 

 of these fish return to the Atlantic, 

 since the traps at La Linea and Ceuta, 

 at the extreme western end of the 

 Mediterranean, are designed to fish 

 the "return" (westward) run only. 



The recovery of two Spanish tags 

 from bluefin tuna caught in a trap 

 near Tripoli, Libya, was reported, but 

 the tags have not been returned, nor 

 have their numbers been ascertained 

 (Rodriguez-Roda 1969a). 



The Atlantic recaptures (15) 

 were much more numerous than those 

 in the Mediterranean (4), but the prob- 

 ability of recapture of a tagged blue- 

 fin seems to have been much greater 

 in the Ibero-Moroccan Bay than in 

 the western Mediterranean. The fish- 

 eries in the former area took many 

 more bluefin in the period 1 960- 1 967 

 than those in the latter. Much more 

 tagging is needed to evaluate the mi- 

 grations between the Atlantic and the 

 Mediterranean quantitatively. 



Much meristic and morphomet- 

 ric data on bluefin tuna from various 

 areas of the eastern Atlantic and the 

 Mediterranean are available, and sev- 

 eral comparisons of the data for fish 

 from different localities have been 

 made (Tiews 1963). Sella (1929a, 

 1930) noted that he had made several 

 observations on tuna from Spain, 

 Calabria (Italy) and Tripoli (Libya), 

 without finding differences sufficient 

 to justify any racial demarcation. He 

 did not, however, publish these data. 

 Frade (1931) concluded that there 

 were significant differences between 

 the tuna which he had examined on 

 the Portuguese coast and those which 

 Heldt (1927b) had measured in Tu- 

 nisia. Nedelec ( 1 954) compared mor- 

 phological data from bluefin tuna cap- 

 tured in the North Sea, off southern 

 Portugal and off Tunisia. He con- 

 cluded that the North Sea samples 

 were close to those from Portugal, 

 but that both differed considerably 



102 



