Mediterranean. Dense concentrations 

 often occur in September and October 

 in the waters just east of the Strait of 

 Gibraltar. No evidence of spawning has 

 been reported from any of these areas. 

 Therefore these fish must have moved 

 some distance from their birthplaces, 

 or there are several undiscovered re- 

 productive areas. A migration from the 

 Black Sea might explain their occur- 

 rences in the Aegean and northeastern 

 Mediterranean Seas. In any case, if blue- 

 fin do move about the Mediterranean 

 during their first year of life, the net 

 result of these movements is disper- 

 sion, in contrast to the strong tendency 

 to concentrate, which is typical in the 

 Atlantic. 



The situation in the eastern Atlan- 

 tic is, as noted previously, dramatically 

 different. Not only are the early stages 

 virtually unknown, but there is very 

 little information on the distribution of 

 the young of the year until October, 

 when they are over 30 cm long. They 

 concentrate off Morocco in that month 

 and in November and remain in the 

 area, usually some distance away from 

 the coast, through the cold season. In 

 June, when they are nearly a year old, 

 they enter coastal waters, where most 

 of them remain through the summer. 

 This appears to be the only regular and 

 important occurrence of age bluefin 

 in the eastern Atlantic. Isolated occur- 

 rences off the Canary and Salvage l.s- 

 lands and Cape St. Vincent have been 

 reported. No one knows from where 

 the young of the year which concen- 

 trate off Morocco come. It is generally 

 assumed that they were hatched in the 

 eastern Atlantic, but we have stated our 

 reasons (Section VIC) for believing tliat 

 many of them may have migrated from 

 the Mediterranean. The tendency of 

 bluefin to concentrate during the first 

 year of life appears to apply in the 

 eastern Atlantic, just as it does in the 

 western side of the ocean, and in con- 

 trast to the dispersion which persists 

 through this phase of life in the Medi- 

 terranean. The eastern Atlantic con- 

 centration forms when the fish are only 

 three or four months old, whereas in 

 the western Atlantic it does not occur 

 until the fish are about a year old. 



b. Small Fish 



The distribution of small fish (50 

 cm- 120 cm long, ages 1-4) in the east- 



em Atlantic somewhat resembles that 

 otTNorth America, but these fish, like 

 the young of the year, are much more 

 widely distributed in the Mediterranean 

 than in the eastem Atlantic. 



The concentration of bluefin which 

 became one year old in late spring or 

 early summer while in the Atlantic 

 coastal waters of Morocco generally 

 remains there, gradually working south- 

 ward along the coast, until late summer 

 or early fall. Then many of them mi- 

 grate northward, arriving otTsouthwest- 

 em Portugal in October or November. 

 Many of these fish spend the cold sea- 

 son there and then continue their north- 

 ward migration in June, entering the 

 Bay of Biscay when thc\' are about two 

 years old. 



In some years, concentrations of 

 age 1 fish occur in the Bay uf Biscay 

 but, again, no one knows whence these 

 tlsh came. Bluefin of all the ages in- 

 cluded in the small size group, as well 

 as older fish, feed in the Bay of Biscay 

 during the warm season. This is the 

 prime nursery and feeding areas for 

 small bluefin in the eastem Atlantic 

 and is analogous to the Middle Atlantic 

 Bight on the ocean's western side. The 

 youngest fish, which are immature, usu- 

 ally remain there for the longest pe- 

 riod. When three-year-olds and most 

 of the four-year-olds are mature, their 

 appearances in tlie Bay are usually brief 

 Some spawning repoiledly occurs in 

 the Bay, which may combine the func- 

 tions of a feeding and a spawning 

 ground for some fish. A few bluefin are 

 reportedly present in the Bay through- 

 out the year, but the fishing season 

 usually extends from early June through 

 October. With the advent of the cold 

 season, the small bluefin leave the Bay 

 and migrate southward to their winter- 

 ing area, which probably centers on the 

 waters between Morocco and the Ca- 

 nary Islands. When the warm season 

 begins, they migrate northward. Dur- 

 ing this movement, numerous fish are 

 often trapped in a hvdrological pocket 

 off the central coast of Morocco and 

 remain there through the season. The 

 fish which avoid this entrapment may 

 follow various courses. The immature 

 fish probably proceed directly to the 

 Bay of Biscay to feed. Some of the 

 mature fish may accompany them and 

 spawn and feed there. Other mature 

 fish may spawn in the Ibcro-Moroccan 



Bay, or, possibly, olT the Moroccan 

 coast before reaching the Bay. Most of 

 the spent fish probably proceed to the 

 Bay of Biscay, completing the migra- 

 tory cycle, but others may join the con- 

 centration off central Morocco. Pre- 

 sumably, all of them return to the win- 

 tering area there when the next cold 

 season arrives. 



Movement patterns of the small 

 bluefin are thus considerably more com- 

 plex in the eastem than in the western 

 Atlantic. Separate summer nursery ar- 

 eas are available, one mainly for age 1 

 fish and the other mainly for older fish. 

 In addition, more than one spawning 

 area is apparently available to the ma- 

 ture fish Thus a variety of migratory 

 patterns may be followed, in confrast 

 to the simple "offshore-inshore" ar- 

 rangement in the western Atlantic. Also, 

 the small bluefin appear to follow a 

 basically north-south migratory pattern 

 in the eastem Atlantic, whereas those 

 in its western waters move seasonally 

 in east-west directions. 



Small bluefin concenfrate in more 

 localities in the Meditenranean than in 

 the Atlantic, and are more available 

 there to year-around fishing. 



Most of the concentrations occur 

 in association with current systems, is- 

 lands, straits, or promontories. Some of 

 these which endure through all, or most, 

 of the year are at the Strait of Messina 

 and Bonifacio (between Sardinia and 

 Corsica) and the Bosporus, the Aeolian 

 Islands and the islands of Malta and 

 Kerkennah, and in the Adriatic Sea. 

 Seasonal concenfrations occur in the 

 Gulf of Lions, the Gulf of Adalia, the 

 Alexandretta-Haifa-Cyprus triangle, the 

 Ionian and Aegean Seas and the Sicil- 

 ian Channel. Most of these are avail- 

 able during most of the warm season, 

 but diminish or disappear during the 

 spawning season in late spring and early 

 summer and during the w inter. Little is 

 known about the migrations of tuna of 

 this size. They are believed to be rela- 

 tively sedcntar)' until they attain matu- 

 rity, usually at ages of three or four 

 years. They then undertake migrations 

 related to reproduction, but the extent 

 of these is unknown. They may be con- 

 fined to the basins to which the fish are 

 native, or they may range throughout 

 the Mediterranean. The spawning ar- 

 eas of the mature small fish are not well 

 known. Probable aieas include the 



136 



