TITLE: Analysis of the Genetic Stock Structure
of the Atlantic Sailfish using Restriction Fragment Length
Polymorphism Analysis of Both Mitochondrial DNA and PCR-Amplified
John E. Graves and Jan R. McDowell
DATE: December 15,
FROM: National Marine Fisheries Service,
Southeast Region, 9721 Executive Center Drive, St. Petersburg,
FL 33702-2432. TELEPHONE: (727) 570-5324
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.