Merten et al.: Genetic structure and dispersal capabilities of Coryphaena hippurus in the western Atlantic 
427 
Caribbean Sea and other areas was small, and their 
movements were largely unidirectional. 
In this study, genes adjacent to the coding region 
were incorporated into genetic analyses to add sensitiv- 
ity to DNA sequence comparisons. The use of the entire 
ND1 gene was considered appropriate to preliminar- 
ily describe the genetic structure of dolphinfish in the 
western central Atlantic at different spatial scales. It 
is important to note that, from the onset of this study, 
the choice to use the ND1 marker may have influenced 
the outcome of results. Therefore, faster-evolving nu- 
clear markers (e.g., microsatellites or single-nucleotide 
polymorphisms) may have been more suitable to detect 
genetic differences of dolphinfish at the scale of this 
study. 
More samples (N>50) should be compared in future 
studies, the sampling area should be expanded to Bra- 
zil and west Africa, and more sensitive markers should 
be used to address the multistock question for dolphin- 
fish across the broader Atlantic. More extensive tag- 
ging studies need to be conducted in poorly sampled ar- 
eas, such as the eastern Caribbean Sea and the Azores 
Islands. Using more sensitive techniques, Diaz-Jaimes 
et al. (2010) detected low genetic structure between the 
Caribbean Sea and Senegal, west Africa, and suggested 
that isolation of dolphinfish in the Mediterranean Sea 
caused genetic differentiation between populations in 
the Mediterranean and western North Atlantic. They 
concluded that alternative markers should be used to 
define stock structure at the within-ocean level. In the 
eastern Pacific, Rocha-Olivares et al. (2006) observed 
significant genetic heterogeneity, using RFLP analy- 
ses of dolphinfish between Hawaii and Baja California 
(straight-line distance= -4660 km); this observation 
was likely the result of lower gene flow among these lo- 
cations but merits future investigation with more pow- 
erful molecular markers (e.g., microsatellites or single- 
nucleotide polymorphisms). In the Caribbean Sea and 
Atlantic, the spatial scale of our study (Miami, Florida, 
to the Azores Islands= -4796 km) was not sufficient to 
resolve stock-related differences. 
Fu’s F s departed significantly from expectations in 
all sampled regions. The driving force of significant de- 
partures from neutrality in our samples was the excess 
of singletons, an outcome that is indicative of past pop- 
ulation expansions (Aris-Brosou and Excoffier, 1996). 
Pairwise mismatch distributions were unimodal for all 
regions, indicating relatively recent range expansions 
with continued gene flow between populations through 
time (Fig. 3) (Rogers and Harpending, 1992; Dfaz-Jai- 
mes et al., 2006). In the central North Atlantic, the low 
number of samples could have heavily influenced the 
extremely low F estimation observed in the mismatch 
analyses (P=0.013). Owing to the low numbers of sam- 
ples from both the eastern Caribbean Sea and central 
North Atlantic, mismatch distributions should not be 
considered conclusive of population expansions until 
more samples are included into future model analyses. 
Because of extensive mixing on a fishery stock level 
and support for a single regionally linked population 
across the sampled region, we suggest that a multi- 
jurisdictional and international approach to manage- 
ment is necessary. The most accurate landings informa- 
tion should be shared among all jurisdicitions where 
dolphinfihs are caught. However, we leave open the 
question of whether the eastern Caribbean Sea can 
be managed separately (though still internationally), 
and it is not clear how the central North Atlantic (i.e., 
Azores Islands) should be grouped as a result of a low 
number of samples; in future studies, more samples 
from this region should be collected and compared. 
Our results are similar to those of Diaz-Jaimes et 
al. (2006), who found a single panmictic eastern Pa- 
cific population of dolphinfish that occurs within the 
northern portion of the Gulf of California and off Chi- 
apas in southern mainland Mexico. The major differ- 
ence between the 2 regions is the number of jurisdic- 
tions where dolphinfish are harvested. In the eastern 
Pacific, the geographic extent of the Diaz-Jaimes et al. 
(2006) study spanned only one exclusive economic zone 
(EEZ); in contrast, as many as 30 EEZs (Mahon, 1996) 
exist in the area examined in our study. Therefore, in 
the western central Atlantic, stock assessments will be- 
come inherently more complex because of the shared 
nature of the resource among many resource users. 
Subsequently, to effectively manage dolphinfish in the 
western central Atlantic, stock assessments need to in- 
corporate the movement of dolphinfish through distant 
and adjacent EEZs, the timing of arrival to different 
EEZs, the amount landed in each location, and the de- 
mographics of this species at different scales. 
Acknowledgments 
This research was supported by funding through the 
U.S. Fish and Wildlife and Puerto Rico Department of 
Natural and Environmental Resources F-66.1 project 
to the Department of Marine Sciences, University of 
Puerto Rico at Mayagiiez. We thank R. Chapman and 
the Marine Resources Division of the South Carolina 
Department of Natural Resources and H. Oxenford 
and N. Simpson of the Centre for Resource Manage- 
ment and Environmental Studies at the University of 
the West Indies for providing additional samples for 
use in this study. We also thank J. Hyde for providing a 
preliminary review on an earlier version of this manu- 
script. Lastly, we thank M. Botello, I. Baez, A. Alfalla, 
C. Whitley, M. Lugo, E. Martinez, M. Carlo, A. Santiago, 
and O. Espinosa for help in the field collecting samples. 
Literature cited 
Allendorf, F. W., N. Ryman, and F. M. Utter. 
1987. Genetics and fishery-management: past, present, 
and future. In Population genetics and fishery man- 
agement (N. Ryman and F. Utter, eds.), p. 1-20. Univ. 
Washington Press, Seattle, WA. 
