GRANT NUMBER:  NA77FD0073         NMFS NUMBER:   96-SER-044

REPORT TITLE:  Analysis of the Genetic Stock Structure of the Atlantic Sailfish using Restriction Fragment Length Polymorphism Analysis of Both Mitochondrial DNA and PCR-Amplified Nuclear DNA

AUTHOR:  John E. Graves and Jan R. McDowell

PUBLISH DATE: December 15, 1999

AVAILABLE FROM:  National Marine Fisheries Service, Southeast Region, 9721 Executive Center Drive, St. Petersburg, FL 33702-2432.  TELEPHONE:  (727) 570-5324

The International Commission for the Conservation of Atlantic Tunas (ICCAT) currently assumes that Atlantic sailfish comprise discrete eastern and western Atlantic stocks.  This model is based on slight differences in morphological characters between fish from the two regions and a lack of trans-Atlantic movements based on tag returns.  However, tag returns have indicated that sailfish are capable of undertaking long-distance migrations, with several movements in excess of 1,000 nautical miles.  In addition, distribution of bycatch of combined sailfish and spearfish by the Japanese longline fishery suggests a continuous distribution.  In order to elucidate the stock structure of Atlantic sailfish, we analyzed both mitochondrial and nuclear DNA from samples taken from both the eastern and western Atlantic.  In addition, several temporal and spatial samples were taken within regions to control for the effects of sampling error.  DNA was purified from 182 fish from the western Atlantic and 134 fish from the eastern Atlantic.  Of the 16 markers screened using a sub-sample from each region, 3 (D-loop, BM-01, BM-10) were found to exhibit a level of variation appropriate to both the sample size and the question being asked.  Although overall genetic diversity was high, no consistent differences were found between fish from the two regions.  The distribution of the alleles between regions, however, weakly supports the current east--west stock hypothesis for Atlantic sailfish.