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Fishery Bulletin 113(4) 
The large population sizes and high dispersal ca- 
pabilities of marine pelagic fishes (e.g., tunas, sword- 
fishes, and jacks) are thought to contribute to low ge- 
netic differentiation among their populations (Graves 
and Dizon, 1989; Graves and McDowell, 2003; Theisen 
et al., 2008). The lack of genetic heterogeneity among 
regional samples in these pelagic species is believed 
to be an outcome of reduced genetic drift due to high 
gene flow among the locations sampled (Hauser and 
Ward, 1998). Studies with the use of various nuclear 
and mitochondrial DNA (mtDNA) markers of yellow- 
fin ( Thunnus albacares ) and bigeye (T. obesus) tuna 
(Graves and Dizon, 1989), striped (Kajikia audax) and 
white (K. albida) marlin (Graves and McDowell, 1994, 
2001), swordfish (Xiphias gladius ) (Alvarado Bremer 
et al., 1996, 2005), and wahoo (Acanthocybium solan- 
dri) (Theisen et al., 2008) have revealed limited intra- 
and interocean divergence. Yet, some pelagic fishes 
(e.g., bluefin tuna [T. thynnus ]) are now recognized as 
distinct species in the Pacific and Atlantic (Collette 
et al., 2001), and others show considerable genetic di- 
vergence among ocean basins (e.g., Indo-Pacific versus 
eastern Pacific, or Gulf of Mexico versus Mediterra- 
nean Sea) owing to physical isolation or the existence 
of separate spawning areas (Graves and McDowell, 
2003). 
In the Atlantic, no genetic heterogeneity has been 
detected over widespread areas for blue marlin ( Mak - 
aira nigricans ) (McDowell et al., 2007), sailfish ( Is - 
tiophorus platypterus) (Graves and McDowell, 2003), 
and wahoo (Garber et al., 2005). High rates of large- 
scale migration and subsequent mixing may reduce the 
probability of small-population structure. For example, 
movement data for blue marlin show transatlantic, in- 
terocean (Atlantic to Indian Ocean), and Atlantic tran- 
sequatorial crossings over large spatial and temporal 
scales, and no subpopulations have been evident (Wit- 
zell and Scott, 1990; McDowell et al., 2007). However, 
population subdivision has been shown between blue- 
fin tuna populations in the Atlantic despite observed 
transatlantic movements between the Gulf of Mexico 
and Mediterranean Sea from satellite and conventional 
tagging data (Boustany et al., 2008). Using microsatel- 
lite and mtDNA markers, Boustany et al. (2008) de- 
tected genetic heterogeneity between those populations 
that was likely the result of strong natal homing to 
either the Gulf of Mexico or the Mediterranean Sea to 
reproduce. 
The dolphinfish (Coryphaena hippurus) is similar 
to many large circumtropically distributed pelagic fish 
species (many thunnins, istiophorids) in that the species 
is abundant and has a high dispersal potential in all 
life stages. However, although istiophorid species have 
varied fecundity (Eldridge and Wares, 1974; Salcedo- 
Bojorquez and Arreguin-Sanchez, 2011) and spawning 
grounds (Richardson, 2008), the dolphinfish is highly 
fecund, spawns throughout a wide geographical range, 
has an early age at first maturity, and a short genera- 
tion time (Palko et al., 1982; Ditty et al., 1994; Benetti 
et al., 1995; Oxenford, 1999). Together, these features 
indicate that genetic differentiation would be limited in 
this species, yet such differentiation has been detected 
at several spatial scales. 
At the largest spatial scale, genetic differentiation 
was reported between eastern Atlantic and western 
Pacific dolphinfish populations, presumably because 
of dispersal limitations and vicariance between basins 
(Diaz-Jaimes et ah, 2010). At the basin-wide scale, 
Diaz-Jaimes et al. (2010), using mtDNA nicotinamide 
adenine dinucleotide (NADH) dehydrogenase subunit 1 
(ND1) sequences, observed genetic divergence between 
the western (Caribbean Sea) and eastern Atlantic (Sen- 
egal). In the Pacific, analyses of mtDNA (Diaz-Jaimes 
et al., 2006) and microsatellite loci (Tripp-Valdez et ah, 
2010) showed no population separation in the Gulf of 
California or eastern central Pacific. However, Rocha- 
Olivares et al. (2006) did show population separation 
using analyses of restriction fragment length polymor- 
phism (RFLP) when comparing dolphinfish sampled in 
the eastern Pacific (Los Cabos, Mexico) and central Pa- 
cific (Hawaii). 
In the past, Oxenford and Hunte (1986) inferred 
population subdivision in the western central Atlan- 
tic from regional differences in peak landings, growth 
rates, size of oocytes, maturity stage of gonads, and a 
limited survey of allozyme variation. Their analyses 
led to the hypothesis that dolphinfish exist as north- 
ern (U.S. East Coast to northern Caribbean Sea) and 
southern (southern Caribbean Sea to Brazil) stocks. 
Around Puerto Rico, anecdotal reports from fisher- 
men and recorded observations support the differen- 
tial timing of the annual arrival of adult dolphinfish 
along the north (fall; October-January) and south 
coast (spring; January-April) (Rivera and Appeldoorn, 
2000). As a result, it has long been thought that these 
seasonal “runs” represent different dolphinfish stocks. 
To examine dolphinfish stock structure around Puerto 
Rico, Rivera and Appeldoorn (2000) examined growth 
rates of dolphinfish sampled around the island to de- 
tect any significant growth differences between the 
northern and southern runs of dolphinfish. Within the 
2 stock hypothesis advanced by Oxenford and Hunte 
(1986), fish around Puerto Rico are thought to belong 
to a northern stock and would, therefore, exhibit much 
slower growth rates than fish in the southern stock 
in Barbados. However, no growth differences were de- 
tected in fish sampled around Puerto Rico or between 
Puerto Rico and Barbados; Rivera and Appeldoorn 
(2000) suggested that stock structure and migration 
patterns were likely to be more complicated than pos- 
tulated by Oxenford and Hunte (1986). 
In this study, we investigated the genetic popula- 
tion structure of dolphinfish around Puerto Rico and 
in the western central Atlantic at 2 spatial scales, us- 
ing the mtDNA ND1 gene. At the larger scale, com- 
parisons were made from distinct regions within the 
western central Atlantic: 1) Puerto Rico (northeastern 
Caribbean Sea); 2) Florida, South Carolina, and North 
Carolina (southeastern United States); 3) Dominica, 
Barbados, and Trinidad and Tobago (eastern Caribbe- 
