3. Maximum Size at which 

 Bluefin Tuna Spawn 



The only authors who have dis- 

 cussed the largest size or age at which 

 bluefin tuna spawn, to our knowledge, 

 are Scaccini et al. (1975). They state 

 that the species spawns "up to the maxi- 

 mum weight and the maximum age" 

 and cite Sari's observation of bluefin 

 tuna estimated to be about 1 8 years old 

 and weighing up to 600 kg, caught in 

 the trap at Favignana (Aegades Islands, 

 just west of the western end of Sicily) 

 in June 1974, as the largest individuals 

 in spawning condition which had been 

 examined by any of them. Since the 

 nimiber of recorded catches of bluefin 

 tuna weighing over 600 kg is negli- 

 gible, it is most unlikely that any sig- 

 nificant number of these fish attain a 

 size at which they cease to spawn. 



I. Discussion and Conclusions 



A discussion and a presentation of 

 our tentative conclusions seem appro- 

 priate, since much of the information 

 in this section is inconclusive and, in 

 many instances, even contradictory. 



1. Mediterranean and Black 

 Seas 



The Mediterranean and Black Seas 

 have traditionally been regarded as 

 prime spawning grounds for the blue- 

 fin tuna. Despite a preponderance of 

 scientific opinion against this concept 

 which developed in the last quarter of 

 the nineteenth century and the first quar- 

 ter of the twentieth, it still appears to be 

 valid. The information now available, 

 however, indicates that the principal 

 reproduction of the eastern Atlantic and 

 Mediterranean bluefin takes place in 

 the south central Mediterranean, instead 

 of occurring in the Black Sea as 

 Aristotle and his followers supposed. 



Small juvenile bluefin were first 

 reported from the Mediterranean by 

 d'Amico (1816). The eggs and larvae 

 were first described briefly by Sanzo in 

 his 1910b publication, and more com- 

 pletely in his 1929 and 1932 works. 

 Some authors have stated that the char- 

 acters presented by Sanzo do not dif- 

 ferentiate the eggs and very small lar- 

 vae of bluefin from those of other tuna- 

 like fishes, especially Auxis. 

 Ehrenbaum's tentative identifications 

 of larval T. thynnns thynnus have been 

 questioned by Sella (1929a) and 

 Richards ( 1 976). Despite these uncer- 



tainties over identifications, there is no 

 doubt that young stages of bluefin have 

 been collected in great numbers in the 

 south central Meditenanean. It is un- 

 fortunate, as noted by Heldt ( 1 930) and 

 Dieuzeide (1951), that Sella did not 

 describe the "thousands" of early stages 

 of bluefin which he (1929a) reported 

 that he had collected. His 1924 pub- 

 lication, however, convinced Richards 

 (1976) of the accuracy of his identi- 

 fications. Scaccini (1961, 1968) and 

 Scaccini et al. (1975), to whom Sella's 

 material was available, also agreed with 

 these identifications. The most numer- 

 ous collections have been made in the 

 Strait of Messina and in waters north 

 and west of Sicily (Sanzo 1932, Sella 

 1924, 1929a; Sparta 1933, Scaccini 

 1968, Piccinetti and Piccinetti Manfrin 

 1970, Scaccini et al. 1975). The de- 

 tailed study of Duclerc et al. (1973) 

 showed that larval bluefin also occurred 

 around the Balearic Islands. Dieuzeide 

 (1951) described three larval bluefin 

 collected off Algeria, and Piccinetti 

 ( 1 973) and Piccinetti et al. ( 1 976b) pre- 

 sented preliminary reports on occur- 

 rences of early stages in the Adriatic 

 Sea. 



Several authors (Vodyanitskii 

 1936, Vodyanitskii and Kazanova 

 1954, Oven 1959) have reported on 

 eggs and larvae of bluefin collected in 

 the Black Sea, but have not produced 

 detailed descriptions. The difficulties 

 of identifying eggs and small larvae of 

 bluefin, even after hatching the eggs 

 and rearing the larvae, have been fully 

 explained by Duclerc etal. (1973) and 

 Scaccini etal. (1975). 



The regular occurrences of great 

 numbers of maturing bluefin along the 

 coasts of westem Sardinia, Tunisia and 

 Tripolitania suggest that spawning oc- 

 curs in those areas as well Although 

 the traps on the eastem (Ionian Sea) 

 coast of Sicily were known as "return" 

 traps, some maturing individuals were 

 caught in them, along with the more 

 numerous spent fish (Sella 1929a, 

 Scordia 1938). Scordia's extensive stud- 

 ies (summarized in her 1938 and 1942 

 publications) indicated that large num- 

 bers of bluefin tuna passed through the 

 Strait of Messina from the lyrrhenian 

 Sea to the Ionian Sea, spawned there, 

 and then returned through the Strait to 

 the Tyrrhenian. It appears that the 



spawning of bluefin tuna in the Mediter- 

 ranean is most intense in its south-cen- 

 tral part, but also extends into the west- 

 em Mediterranean and the Adriatic Sea. 

 As Scaccini et al. (1975) concluded, 

 additional research will probably show 

 that bluefin spawn in other parts of tlie 

 Mediterranean. Some spawning must 

 also occur in the Black Sea. The ab- 

 sence of a commercial fishery for the 

 species there, however, and the rela- 

 tively small catches taken in its ap- 

 proaches, the Bosphorus and the Sea of 

 Marmara, suggest that the reproduc- 

 tion there is not comparable, quantita- 

 tively, to that in the central Mediterra- 

 nean. 



2. Eastern Atlantic 



The situation in the eastem Atlan- 

 tic is dramatically different from that in 

 the Mediterranean and Black Seas. De- 

 spite extensive research efforts over 

 many decades, no identifiable early 

 stages of bluefin have been collected in 

 the Ibero-Moroccan Bay, which has 

 been regarded as the prime spawning 

 ground in the region, or in the more 

 recently suggested areas of reproduc- 

 tion off Morocco and in the Bay of 

 Biscay. The only identified early stages 

 from the eastem Atlantic were collected 

 near the Equator between longitudes 

 0° and 15=30'W (Richards 1969, 

 Richards and Simmons 1971). This was 

 a totally unexpected area on the basis 

 of existing knowledge of the distribu- 

 tion of maturing bluefin. It certainly 

 merits further investigation to deter- 

 mine the seasonal and areal extent of 

 the occurrence, and also to make cer- 

 tain that the larvae are actually those of 

 T. thynnus ihynnus rather than those of 

 T maccovll, which also occurs in the 

 South Atlantic. 



Regular seasonal occurrences of 

 very numerous maturing and spent blue- 

 fin in the Ibero-Moroccan Bay have 

 been abundantly documented. Small 

 numbers of maturing or ripe bluefin in 

 the Bay of Biscay have been reported 

 occasionally (Creac'h 1952, Le Gall 

 1952) and detailed studies of the go- 

 nads of a few individuals have just 

 become avai lable (Cort et al. 1 976, Cort 

 1977). The occurrence of small num- 

 bers of mature bluefin at the Azores 

 has been reported (Ferreira 1932), but 

 no details on their gonad condition were 

 presented. 



94 



