dition data from German North Sea 

 catches of bluefm tuna, Tiews (1964) 

 estimated the percentage of the yearly 

 late season (September 15-October 

 31) catches there which probably 

 were recruited from the western At- 

 lantic in the years 1952-1962 The 

 percentage recruited vaned from 39 

 of the 1953 catch to m 1957 and 

 1959. After 1954, the first year m 

 which bluefm were tagged in the 

 Sfraits of Florida, the maximum esti- 

 mated recruitment of western Atlan- 

 tic fish to the northeastern Atlantic 

 occurred in 1960 (11%) and 1961 

 (33%) (Table 28). Two tagged fish 

 migrated directly from the Bahamas 

 to Norway m 1961. Two others, re- 

 leased in 1960 and recaptured in 

 1962, were in the normal late-season 

 fat condition when recaptured, indi- 

 cating that they had probably crossed 

 the Atlantic during a previous year 

 (1960 or 1961), and spent their last 

 summer in the feeding grounds ofl' 

 northern Hurope. Thus the results of 

 the tagging, limited as they are, are 

 quite consistent with the estimates of 

 recruitment based on body condition 

 (Table 28) 



To sum up, even though the ma- 

 jority of the returns from releases of 

 giant bluefin in the Straits of Florida 

 have been from Norwegian waters, 

 the following facts, or deductions, 

 suggest that these returns do not rep- 

 resent a part of a normal annually 

 repeated migratory pattern: 



1 . The fish are in waters where 

 food is scarce during the penod when 

 giant bluefin are normally feeding 

 heavily in nch coastal areas and re- 

 gaining the weight they have lost dur- 

 ing their spawning activity and the 

 related migrations 



2. The transatlantic migrations 

 have not been randomly distributed 

 over the yeais, but have occurred in 

 clusters in certain periods. 



3 . Tiews' ( 1 964) estimates of an- 

 nual recruitment of giant bluefin from 

 the western Atlantic in the late sea- 

 son North Sea fishenes, based on 

 body condition data, also show thai 

 this recruitment is very irregular, with 

 peaks of high recruitment separated 

 by long periods of negligible recruit- 

 ment. 



4. The variations in annual re- 

 cruitment, as estimated by Tiews 



(1964), are consistent with those in 

 transatlantic migrations indicated by 

 tag returns, tor those years in which 

 both types of data are available 



5. Rodewald (1967) has shown 

 that the volume of west-east transat- 

 lantic migration may have been in- 

 fluenced positively by anomalies in 

 the atmospheric circulation over the 

 North Atlantic which produce excep- 

 tionally strong west winds in the 

 middle latitudes in certain years His 

 findings were generally consistent 

 with the tag return data and Tiews' 

 (1964) estimates of annua! re- 

 cruitment 



6 The two giant bluefin tuna 

 which were recaptured in Norwegian 

 waters in August and September 

 1962, 26-27 months after they had 

 been tagged off Bahamas, were m 

 the noiTnal fat condition which is typi- 

 cal of fish which have been feeding 

 heavily in coastal waters Rodewald 

 (1967), moreover, found that atmo- 

 spheric conditions over the probable 

 migration route in July 1962 were 

 distinctly unfavorable for movements 

 from west to east It is highly prob- 

 able that these fish had crossed the 

 Atlantic in a previous year, and then 

 entered into the migratory pattern fol- 

 lowed by large bluefin in the eastern 

 Atlantic 



On the basis of this evidence, we 

 conclude tentatively that recruitment 

 of large bluefin to the northeastern 

 Atlantic from the western Atlanfic is 

 variable, being important in some 

 years and negligible in others We 

 speculate further that at least some of 

 these recruits remain in the eastern 

 Atlantic through the next annual feed- 

 ing period, or longer 



No east-west transatlantic migra- 

 tions of large bluefin tuna have been 

 recorded. Although 554 large and me- 

 dium-sized bluefin were lagged in 

 the eastern Atlantic oft' Nonvay and 

 Spain prior to 1968, none of the 51 

 recoveries has been west of longi- 

 tude 10°W (FAO 1972) A renewed 

 and sustained lagging program is re- 

 quired to detennine whether such mi- 

 grations occur 



ii. Medium Fish 



While there is no direct evidence 

 of medium sized fish making the mi- 

 gration from North America to Eu- 

 rope, there remains the possibility 



that several fish tagged and released 

 as small sized fish could have made 

 the migration and been recaptured as 

 medium sized fish. 



iii. Small fish 



Tag returns have demonsfrated 

 transatlanfic migrations of 40 small 

 (less than 20 kg when tagged) blue- 

 fin tuna from west to east, and two 

 from east to west (Figure 75). 



All of the west-east migrations 

 were from the New Jersey-Cape Cod 

 area to the Bay of Biscav (Mather 

 1 960, 1 969; Mather et al, f967, FAO 

 1972). All of the releases took place 

 in July and August, and the recap- 

 lures extended over the period from 

 June through October in subsequent 

 years. Therefore, these migrations 

 evidently occurred mainly in the cold 

 seasons belw cen the departure of the 

 small bluefin from American coastal 

 waters in late September or October, 

 and their arrival in the Bay of Biscay 

 in late May or early June. The mini- 

 mum distance travelled was about 

 3,000 nautical miles (5,500 km) and 

 the minimum time at large was 1 1 

 months The average speed required 

 would be only 4 knots (0 7 km/hr). 

 It is possible, however, that the times 

 at large were influenced by the eight 

 month period (October-May) in 

 which there was little or no fishing 

 for small bluefin. 



The 40 west-east transatlantic 

 migrations of small bluefin have not 

 been randomly distributed over the 

 years Thirty-eight of them could 

 have occurred in a minimum of three, 

 and a maximum of five cold seasons 

 between 1965 and 1969 The other 

 two could have taken place in a mini- 

 mum of one, and a maximum of two 

 periods between 1954 and 1959. 

 Thus, over a 22 year period, all mi- 

 grations of this nature revealed by 

 tag returns could have occurred in a 

 minimum of four, and a maximum of 

 seven winter periods. All of the re- 

 tuins were from only four of 22 yearly 

 release groups Two of these groups, 

 however, 1,938 in 1965 and 3,959 in 

 1 966, were the largest On the other 

 hand, the 1 69 releases in 1 954 yielded 

 two transatlantic returns at a time 

 when tuna tagging was a relatively 

 unknown practice, and larger num- 

 bers of releases in 1 955, 1 964, and in 

 1968-1975 after tagging had been 



130 



