and G₆PD (glucose-6-phosphate dehydrogenase). Allele frequencies at SOD-1 between the two samples did not differ significantly, whereas allele frequencies at SOD-2 (G = 12.11, P < 0.01) and G₆PD (G = 137.19, P < 0.001) did differ significantly. There was evidence for a null allele at SOD and for artifacts of G₆PD banding, indicating that the differences between samples must be interpreted with caution. In addition, the sample of late-arriving fishes was small (n = 16).

Bartlett and Davidson (1991) sequenced 290 bp of the cyt b gene and found six mtDNA haplotype among 33 individuals of Atlantic bluefin tuna; 28 of the fish shared a single haplotype. The common haplotype differed from four others by one nucleotide substitution and from one other by two substitutions. Because the portion of the cyt b gene sequenced by Bartlett and Davidson (1991) generally is conserved in other scombroids (e.g., swordfish [Finnerty and Block, 1992]), it likely will not be informative for resolving population structure in Atlantic bluefin tuna. Other regions of the mtDNA molecule (e.g., the D-loop) are more variable and thus may be more suitable for resolving population structure in bluefin tuna.

To date, molecular genetic studies of bluefin tuna have not focused on the issue of genetic divergence among global samples of bluefin tuna. The genetic analysis of within-ocean basin diversity of Atlantic bluefin tuna (e.g., Atlantic Ocean, Mediterranean Sea), would benefit from a worldwide study of molecular genetic variation among bluefin tuna. Molecular genetic studies in other highly migratory, scombroid fishes (tunas, marlins, and swordfish) have demonstrated the utility of such an approach (Appendix C), and a thorough analysis of nucleotide sequence variability in both mtDNA and rapidly evolving nuclear DNA (micro-and/or minisatellite loci) in Atlantic bluefin tuna should be encouraged.

There is less genetic information available for Atlantic bluefin tuna than for other scombroid fish. The studies of Edmunds and Sammons (1971, 1973) are consistent with the hypothesis that eastern and western management units of Atlantic bluefin tuna comprise a unit Mendelian population (i.e., they are genetically homogeneous). The remaining studies are either incomplete or inadequate to address the issue.

A major research effort should be undertaken to thoroughly assess the genetic basis of the population structure of Atlantic bluefin tuna. Multiple genetic characters, detected by a variety of approaches, should be employed to provide information on several fundamental questions and to resolve the issue of stock structure. It is critical to support a variety of genetic studies.

Front Matter (R1-R18)

Summary (1-4)

1 Background (5-8)

2 Historical Evidence for Stock Structure (9-38)

3 Transatlantic Movement of Atlantic Bluefin Tuna (39-78)

4 Fish Stock Assessment (79-108)

5 Conclusions and Recommendations (109-112)

References (113-118)

Appendix A: Biographical Sketches of Committee Members (119-122)

Appendix B: Bibliography (123-126)

Appendix C: Genetic Variation in Other Tunas and Related Fish (127-134)

Appendix D: Archival Tag Technology (135-138)

Appendix E: Evidence for Mixing Based on Parasites (139-146)

Appendix F: Microconstituent Analysis (147-148)