in response to various stimuli. Changes 

 in the currents, in the water tempera- 

 ture, or in the availabihty of food may 

 affect its migratory behavior. Popula- 

 tion pressure, either within the species 

 itself or from competing species, may 

 also be an influencing factor. Even in 

 apparently stable conditions, the dis- 

 tributional behavior of the bluefin does 

 not confine it to sft-ictly limited sea- 

 sonal habitats. These proposed migra- 

 tory patterns should, therefore, be re- 

 garded as tendencies with which a ma- 

 jor portion of the fish are apt to con- 

 form in a general way, rather than fixed 

 routes followed by entire size groups. 



2. Western Atlantic 



a. Very Small Fish 



During their first year of life, blue- 

 fin tuna (less than 50 cm long) in the 

 western North Atlantic migrate consid- 

 erable distances from extensive and in- 

 completely defined spawning grounds 

 to the warm season nursery area for 

 small (50 cm- 120 cm) bluefin in the 

 Middle Atlantic Bight. They form tlieir 

 first regular and stable concentration 

 there in late June or early July when 

 they are approximately one year old. 

 The net movement during this first year 

 is basically one of concentration. The 

 routes are unknown, but they are prob- 

 ably varied and devious. 



Their wide distribution in their first 

 weeks of life has been established by 

 collections of larvae and small (less 

 than 122 mm long)juvenilesover much 

 of the Gulf of Mexico and off the coast 

 from southern Florida to New Jersey. 

 Their movements during the interven- 

 ing period are not known. Small and 

 usually brief concentrations of new- 

 bom fish occasionally occur in the Cape 

 Cod-Cape Hatteras area beUveen late 

 July and November. Tag retums have 

 shown that some of these fish, at least, 

 return to the area when they are one or 

 two years old. Scattered occurrences 

 suggest distribution along the United 

 States coast from Cape Cod to the Mexi- 

 can border during the warm season, 

 and from Cape Hatteras to southern 

 Florida in tlie colder months. Thus these 

 fish may visit various areas during their 

 first year of life. Occasional mid-sum- 

 mer schooling in the Straits of Florida 

 suggests a migration from the Gulf of 

 Mexico to the Cape Hatteras-Cape Cod 

 area. Such a migration seems reason- 



able, since the most important repro- 

 duction of bluefin in the western Atlan- 

 tic evidently occurs in the ( iult, and the 

 only known warm concentration of 

 yearlings in the region takes place in 

 the Middle Atlantic Bight. 



There is a great need lor extensive 

 tagging of age bluefin when they 

 appear in the Sfraits of Florida. Any 

 same season recoveries from fish tagged 

 in this area would give a much more 

 definite indication of their distribution 

 during the first year. Tliis is one essen- 

 tial gap in our understanding of the 

 bluefin's life history. 



b. Small Fish 



Small bluefin (50 cm to 120 cm 

 long, ages I -4) concentrate in the nurs- 

 ery and feeding area between Cape 

 Hatteras and Cape Cod during the warm 

 season. They tend to move northeast- 

 ward along the coast as (he season ad- 

 vances, and their range has extended 

 into the southwestern Gulf of Maine in 

 some years. The oldest fish in the group 

 tend to pass through this area first, fol- 

 lowed by successively younger age 

 groups. When the waters cool in Octo- 

 ber and November, they move ofishore. 

 Their wintering area, as indicated by 

 recent tag retums, is in oceanic waters 

 not far from the edge of the continental 

 shelf off New England, Long Island 

 and New Jersey. They occupy subsur- 

 face waters in this period and grow 

 much more slowly than during the 

 warm season. During late May and June 

 they tend to concentrate and move in- 

 shore to their summer habitat. A few of 

 these fish may attain their first maturity 

 near the end of their third year of life, 

 and many more near the end of their 

 fourth year. These fish probably spawn 

 in this same wintering area in late May 

 or June. Thus a special spawning mi- 

 gration is not required and all of the 

 fish in this group follow a two-phase 

 migratory pattern between their feed- 

 ing and wintering areas, with the ranges 

 of the fish increasing slightly with each 

 additional year of age. The available 

 facts show that this is an east-west mi- 

 gration, in contrast to the north-south 

 pattern which has been, and continues 

 to be, surmised. 



In a few years, tag returns have 

 revealed migrations of small bluefin 

 (one or nvo years old when released) 

 from the Middle Atlantic Bight to the 

 Bay of Biscay. These appear to have 



been unusual occurrences, rather than 

 part of a regular migrator)' pattern, as 

 noted in Section VIC. They will be 

 discussed further in the context of stock 

 identification. 



c. Medium Fish 



The distribution pattern of the me- 

 dium (120 cm to 185 cm long, 5 to 

 about 7 years old) bluefin in the west- 

 em Atlantic differs mainly from that of 

 the small fish in its eastward extent. In 

 recent years, their warm season distri- 

 bution and movements have been very 

 similar to those of the small fish, ex- 

 tending from Cape Hatteras to Cape 

 Cod. Until 1 966, they were often abun- 

 dant in the southwestern Gulf of Maine 

 from early August through October and 

 sometimes into November and also 

 along the Nova Scotian coast from 

 Yarmouth to Halifax. They usually ar- 

 rived in, and departed from, these north- 

 em waters later than the larger and 

 smaller fish which were present. Fish 

 of this size, however, have very seldom 

 been taken north of Cape Cod in sig- 

 nificant numbers since 1966. Their 

 maximum seasonal abundance south 

 of Cape Cod is rather unpredictable, 

 occurring early in the season in some 

 years and as a late season concentra- 

 tion in others. 



These fish, like the small ones, 

 move offshore when the water cools in 

 the fall. Many of them concentrate in 

 the canyons along the edge of the con- 

 tinental shelf in November, and then 

 resume their offshore movement. Part 

 of their wintering area coincides with 

 that of the small fish. It extends east- 

 ward between the edge of the continen- 

 tal shelf and the Gulf Stt-eam north of 

 Cape Hatteras at least to the southem 

 tip of the Grand Banks. 



Most, if not all, of the fish in this 

 group are mattire, but their spawning 

 area has not been defined. Limited ex- 

 plorations have located concentrations, 

 including maturing fish, near the north- 

 em edge of the Gulf Stt-eam south of 

 southem New England and George's 

 Bank in late May and early June, but 

 this probably is only a part of the spawn- 

 ing area. As in the case of the small 

 fish, spawning apparently does not re- 

 quire much deviation from the direct 

 routes between the summering and 

 wintering areas. The concentt-ations 

 which fomi near the Gulf Stt-eam in 

 May and early June move inshore and 



1.14 



