southeastern comer of the Tyrrhenian 

 Sea and the Ionian Sea off Sicily, the 

 coast of Libya eastward to Bengasi, 

 and the Balearic Islands. The small fish 

 spawn considerably later than the larger 

 ones. Their reproductive season extends 

 through July and well into August; some 

 even spawn in September. As with the 

 young of the year, the distribution of 

 the immature small fish is much greater 

 than that of the known spawning area. 

 Again, this implies some migration by 

 these fish, unless the reproductive ar- 

 eas are much more extensive than is 

 now known. The tendency for small 

 bluefin to concentrate seasonally in one 

 or two relatively small areas, which is 

 so pronounced on both sides of the 

 Atlantic, is not evident in the Mediter- 

 ranean. 



c. Medium Fish 



While the bluefin in the eastern 

 Atlantic and the Mediterranean are in 

 the medium size range (120 cm- 185 

 cm long, from 5 to about 8 years old), 

 their ranges begin to overlap. This 

 greatly complicates the tracing of their 

 life histories and adds correspondingly 

 to the uncertainties of existing knowl- 

 edge about their life cycles. The dis- 

 tribution and migratory patterns of the 

 medium fish in the eastern Atlantic are, 

 or have been, more extensive than those 

 of the small fish. It is more difficult to 

 assess these differences in the Mediter- 

 ranean. 



Virtually all of the medium fish in 

 this region are mature, but their spawn- 

 ing habits are not well known. Tlney 

 spawn later than the large individuals- 

 probably through all of July in the east- 

 em Atlantic, and into August in tlie 

 central Mediterranean. 



In recent years, the migrations of 

 medium fish in the eastem Atlantic have 

 been similar to those attributed to the 

 mature small fish, with the exception 

 that some medium fish, at least, enter 

 the Mediterranean. Most of these fish 

 migrate from their wintering area off 

 northwestem Africa (which probably 

 extends from latitude 35°N to latitude 

 1 5°N and from the coast to longitude 

 20° W) to the Ibero-Moroccan Bay or 

 nearby waters, where the majority of 

 them presumably spawn. Some of them, 

 in numbers which vary from year to 

 year, migrate along the coasts of the 

 bay in the "arrival" ran in which large 

 fish are usually predominant. An un- 



known, but probably small, percentage 

 of these medium fish enter the Medi- 

 terranean with more numerous large 

 fish and spawn there. These fish, and 

 most of those which have spawned in 

 the Ibero-Moroccan Bay or adjacent 

 Atlantic waters, then migrate to the feed- 

 ing grounds in the Bay of Biscay. Some 

 of them participate in the "retum" nin 

 with the large spent fish and others 

 migrate separately. Still other tish may 

 travel directly from the wintering area 

 to the Bay of Biscay and reproduce in 

 the secondary spawning area which ap- 

 parently exists there. The medium fish 

 are usually most abundant in the Bay 

 of Biscay from mid July to mid August 

 or September. Their whereabouts there- 

 after is unknown until they presumably 

 return to their wintering area in late 

 fall. A secondary feeding area exists 

 off the central coast of Morocco. Some 

 medium fi.sh may go there, rather than 

 to the Bay of Biscay, after spawning in 

 the Ibero-Moroccan Bay or the Medi- 

 terranean. Others possibly visit this area 

 after leaving the Bay of Biscay. All of 

 these fish probably retum to the same 

 wintering area in late fall. Until 1962, 

 large numbers of medium bluefin mi- 

 grated from their spawning ground to 

 feeding grounds also used by large blue- 

 fin off the southwestern coast of Nor- 

 way, passing west and north of the 

 British Isles en route. They usually ar- 

 rived there in mid or late July, and 

 departed in late October. They rounded 

 the British Isles again en route south to 

 their wintering area. Since 1962, few 

 medium fish have been taken north of 

 the Bay of Biscay. Their coastal feed- 

 ing thus became similar to that of the 

 small fish. As noted previously, a com- 

 parable change in the summer distribu- 

 tion of medium bluefin in the western 

 Atlantic occurred in 1 962 These range 

 reductions may have been related to 

 the great decline in the apparent abun- 

 dance of fish of this size group which 

 occurred all over the Atlantic in this 

 period, and has subsequently affected 

 the Mediterranean. 



The distribution of medium blue- 

 fin in the Mediterranean Sea is quite 

 similar to that of the small fish. Both 

 groups often share the same habitats, 

 or adjacent ones. Medium fish are usu- 

 ally predominant, however, off the east 

 coast of Spain. The medium fish pre- 

 sumably migrate farther than the small 

 ones, but their migratory patterns are 



not known. Tlieir concentrations tend 

 to remain more or less stationary in a 

 given area for a few weeks and then 

 disappear. One of these absences oc- 

 curs during the spawning season, which 

 probably extends from late June into 

 August. Spawning migrations begin 

 earlier, in May or June. The directions 

 and distances of these migrations are 

 probably quite variable. Many medium 

 fish participate in the eastward "arrival" 

 run of maturing bluefin in May and 

 June. This run is believed to include 

 many large and some medium fish from 

 the eastern Atlantic, but more medium 

 fish than large ones from the Mediter- 

 ranean. The medium fish are usually 

 most numerous in the later part of this 

 run, and favor the more easterly areas, 

 such as the southeastem Tyrrhenian Sea 

 and the waters off eastem Tunisia and 

 Libya. The waters in these areas are 

 somewhat warmer and more saline than 

 those in the more westerly areas fa- 

 vored by the large fish. "Resident" me- 

 dium fish also participate in the west- 

 ward "retum" ran of spent fish in July 

 and August. Probably many of the old- 

 est fish in this group accompany this 

 migration into the Atlantic, shifting into 

 the wider ranging pattem of the "giant" 

 fish. This would occur when the fish 

 are about 185 cm long and about 9 

 years old. Most of the younger "resi- 

 dent" fish probably remain in the Medi- 

 terranean. 



d. Large Fish 



Under the hypothesis which we 

 regard as the best explanation of the 

 available facts, the large bluefin in the 

 eastem Atlantic and the Mediterranean 

 may be regarded essentially as a single 

 aggregation offish. 



The wintering area occupied by 

 the majority of this group has not been 

 defined. Probably most of the fish win- 

 ter in the Atlantic between latitudes 

 20°N and 35°N and the African coast 

 and longitude 30" W, but the total win- 

 tering area may extend much farther, 

 especially to the south. 



Relatively small groups of large 

 bluefin winter in certain localities in 

 the Mediterranean-Black Sea system 

 where food is plentiful, particularly off 

 the mouth of the Rhone and in the 

 Bosporus. There are two possible ex- 

 planations of these occurrences. The 

 groups may comprise a resident Medi- 

 terranean stock (or stocks). On the other 



137 



