the same sizes from the eastern and 

 the western Atlantic. These studies 

 indicated that the heads and the pec- 

 toral fins of individuals from the east- 

 ern Atlantic were slightly shorter than 

 those of mdividuals from the west- 

 em Atlantic, and that the maximum 

 depths of the fonner were slightly 

 less than those of the latter, even 

 allowing for seasonal changes in this 

 characteristic. Comparisons of mer- 

 istic data, particularly gill raker 

 counts, by Robins (1957), Mather 

 (1959) and Tiews (1963) showed no 

 significant differences between large 

 samples of fish from the two areas. 



In a more recent study, Rivas 

 (Rivas and Mather 1976), however, 

 did not find significant differences in 

 the characteristics noted above be- 

 tween the samples from the two ar- 

 eas. He did, however, show diver- 

 gences in the pectoral ray counts and 

 in the counts of gill rakers in juve- 

 niles 27 to 118 mm long. He also 

 found that the average length of the 

 second dorsal fin was significantly 

 greater for bluefin from the western 

 Atlantic than for those from the east- 

 em Atlantic. Previous authors had 

 not noted this difference. Since Rivas 

 and Mather have been in contact for 

 many years, and have followed the 

 same methods as closely as possible, 

 these discrepancies show how diffi- 

 cult it is to obtain consistent results 

 from biometnc studies The prelimi- 

 nary results suggest, however, thai 

 there may be distinct stocks of blue- 

 fin tuna on the two sides of the At- 

 lantic. Extensive data for more ex- 



haustive studies are available at the 

 Woods Hole Oceanographic Institu- 

 tion and the Southeast fisheries Sci- 

 ence Center, National Marine Fish- 

 eries Service, Miami, Flonda, and in 

 the literature: Hcldt (1927) [Tuni- 

 sia], l-'rade (19.31) [Portugal], Russell 

 1934a [North Sea], Navaz (1950a) 

 (Bay of Biscay], Nedelec (1954) 

 [North Sea], iiuser-Lahaye and 

 Doumenge (1954) and Doumenge 

 and Lahaye ( 1953) [Mediterranean 

 coast of France], Arico and Gcnovese 

 (1953), and Genovese (1957, 1958) 

 [Tyrrhenian Sea], and Morovic 

 (1968) [Adriatic Sea]. European 

 workers have taken their measure- 

 ments with tapes, following the con- 

 tour of the body (Anonymous 1 932b), 

 whereas United States workers have 

 taken "straight line" measurements 

 with calipers (Marr and Schafer 

 1949) Factors for converting 

 "straight" measurements of north- 

 western Atlantic bluefin to the 

 "curved" system are available at the 

 Woods Hole Oceanographic Institu- 

 tion 



ii. Biochemical Studies 



Edmunds and Sammons (1971, 

 1973), after studying the genic poly- 

 morphism of tetrazolium oxidase in 

 bluefin tuna from the western North 

 Atlantic and from the Atlantic coast 

 of France using clcctrophoretic tech- 

 niques, concluded that no differences 

 could be found between the samples 

 from the two areas. On this basis, 

 and the indications of sporadic trans- 

 atlantic migrations from tagging, they 



tentatively concluded tiiat the blue- 

 fin tuna of the two areas belonged to 

 a single breeding population rather 

 than two geographically distinct 

 stocks The>' noted that the evidence 

 was not conclusive and that other 

 hereditary characters might reveal a 

 degree of racial separation that was 

 not apparent from a comparison based 

 on the Ox-1 enzyme system 



iii. Conclusions 



In our opinion, neither the bio- 

 metnc nor the biochemical studies 

 have provided conclusive evidence 

 in regard to the identity of the stock, 

 or slocks, of bluefin tuna in the At- 

 lantic Ocean and adjacent seas. 

 Fumestin and Dardignac (1962) have 

 previously expressed this opinion in 

 regard to the biometric studies avail- 

 able at that date Tiews (1963) did 

 not believe that the difterences be- 

 tween samples of bluefin tuna from 

 different areas which had been pro- 

 posed by various authors would stand 

 up under critical inspection. The bio- 

 chemical studies now available are 

 admittedly of a preliminary nature 

 and were based on samples which 

 were not sufficiently numerous to 

 provide definitive results 



It IS our opinion that the identifi- 

 cation of stocks must be based largely 

 on distnbufional studies and tagging 

 results Hypotheses in regard to the 

 identity' of stocks, as well as migra- 

 tor)' patterns, will be discussed in 

 Section VIIE, the concluding part of 

 this work. 



132 



