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1.
Pop-up satellite archival tags were implanted into 68 Atlantic bluefin tuna (Thunnus thynnus Linnaeus), ranging in size from 91 to 295 kg, in the southern Gulf of Maine (n=67) and off the coast of North Carolina (n=1) between July 2002 and January 2003. Individuals tagged in the Gulf of Maine left that area in late fall and overwintered in northern shelf waters, off the coasts of Virginia and North Carolina, or in offshore waters of the northwestern Atlantic Ocean. In spring, the fish moved either northwards towards the Gulf of Maine or offshore. None of the fish crossed the 45°W management line (separating eastern and western management units) and none traveled towards the Gulf of Mexico or the Straits of Florida (known western Atlantic spawning grounds). The greatest depth recorded was 672 m and the fish experienced temperatures ranging from 3.4 to 28.7°C. Swimming depth was significantly correlated with location, season, size class, time of day, and moon phase. There was also evidence of synchronous vertical behavior and changes in depth distribution in relation to oceanographic features.Communicated by J.P. Grassle, New Brunswick 相似文献
2.
We examined movements of Atlantic blue marlin (Makaira nigricans) from the Gulf of Mexico based upon 42 pop-up archival transmitting (PAT) tags. Long deployments (including one 334-day track)
revealed diverse movement patterns within the Gulf of Mexico. North–south seasonal changes in blue marlin distribution showed
strong correspondence with established seasonal patterns of sea surface temperature and primary production. During the summer
spawning season, blue marlin utilized outer shelf and shelf edge waters in the northern Gulf of Mexico, and longer duration
tracks indicated overwintering habitats in the Bay of Campeche. Egress occurred throughout the year and was difficult to determine
because some tracks ended in the Straits of Florida (n = 3) while other tracks recorded movement through it or the Yucatan Channel (n = 4). Our results indicate that Atlantic blue marlin have a more restricted geographic range of habitats than previously
recognized and that the Gulf of Mexico provides spatially dynamic suitable habitat that is utilized year-round through seasonal
movements. 相似文献
3.
This study is the first report of post-nesting migrations of loggerhead sea turtles (Caretta caretta) nesting in Sarasota County (Florida, USA), their most important rookery in the Gulf of Mexico (GOM). In total, 28 females
(curved carapace length CCL between 82.2 and 112.0 cm) were satellite-tracked between May 2005 and December 2007. Post-nesting
migrations were completed in 3–68 days (mean ± SD = 23 ± 16 days). Five different migration patterns were observed: six turtles
remained in the vicinity of their nesting site while the other individuals moved either to the south-western part of the Florida
Shelf (n = 9 turtles), the Northeast GOM (n = 2 turtles), the South GOM (Yucatán Shelf and Campeche Bay, Mexico, and Cuba; n = 5 turtles) or the Bahamas (n = 6 turtles). In average, turtles moved along rather straight routes over the continental shelf but showed more indirect
paths in oceanic waters. Path analyses coupled with remote sensing oceanographic data suggest that most of long-distance migrants
reached their intended foraging destinations but did not compensate for the deflecting action of ocean currents. While six
out of seven small individuals (CCL < 90 cm) remained on the Florida Shelf, larger individuals showed various migration strategies,
staying on the Florida Shelf or moving to long-distance foraging grounds. This study highlights the primary importance the
Western Florida Shelf in the management of the Florida Nesting Subpopulation, as well as the need of multi-national effort
to promote the conservation of the loggerhead turtle in the Western Atlantic.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
The transport of eel early life stages may be critical to their population dynamics. This transport from ocean spawning to
freshwater, estuarine and coastal nursery areas is a combination of physical and biological processes (including swimming
behavior). In New Jersey, USA, the American eel (Anguilla rostrata) enters estuaries as glass eels (48.7–68.1 mm TL) in contrast to the Conger eel (Conger oceanicus) that enters as larger (metamorphosing) leptocephali (68.3–117.8 mm TL). To begin to understand the mechanisms of cross-shelf
transport for these species, we measured the potential swimming capability (critical swimming speed, U
crit) under ambient conditions throughout the ingress season. A. rostrata glass eels were collected over many months (January–June) at a range of temperatures (4–21°C), with relative condition declining
over the course of the ingress period as temperatures warmed. C. oceanicus occurred later in the season (April–June) and at warmer temperatures (14–24.5°C). Mean U
crit values for A. rostrata (11.7–13.3 cm s−1) and C. oceanicus (14.7–18.6 cm s−1) were comparable, but variable, with portions of the variability explained by water temperature, relative condition, ontogenetic
stage, and fish length. Travel times to Little Egg Inlet, New Jersey, estimated using 50% U
crit values, indicate it would take A. rostrata ~30 and ~60 days to swim from the shelf edge and Gulf Stream, respectively. Travel times for C. oceanicus were shorter, ~20 days from the shelf edge, and ~45 days from the Gulf Stream. Despite differences in life stage, our results
indicate both species are competent swimmers, and suggest they are capable of swimming from the Gulf Stream and/or edge of
the continental shelf to estuarine inlets. 相似文献
5.
Phyllorhiza
punctata, commonly called the Australian white spotted jellyfish, invaded the Caribbean in the 1960s, becoming established there and
subsequently in the United States in the northern Gulf of Mexico (by 2000) and eastern Florida (2001). With the prevailing
Loop Current flowing clockwise around the Gulf of Mexico and joining the Gulf Stream along eastern Florida, potential transport
of P. punctata along the eastern seaboard of the USA could be facilitated. P. punctata medusae were collected in small numbers along the entire Georgia coast during May–November in 2007 and 2008. Medusa bell
diameters increased both years from ca. 10 cm in May to ca. 33 cm in autumn. Specimens lacked zooxanthellae, as reported for
medusae in the northern Gulf of Mexico and Florida. It is possible that the P. punctata medusae observed were transported from established populations to the south; however, whether or not this species is established
along the Georgia coast has yet to be determined. 相似文献
6.
Amanda C. O’Toole Andy J. Danylchuk Tony L. Goldberg Cory D. Suski David P. Philipp Edd Brooks Steven J. Cooke 《Marine Biology》2011,158(10):2227-2237
Great barracuda (Sphyraena barracuda) were implanted with acoustic telemetry transmitters (n = 42) and monitored within a stationary acoustic receiver array (n = 53 receivers) in The Bahamas to examine residency, seasonal movements, and habitat use. Barracuda were monitored for up
to 980 days and remained within the array area ~33% (median value) of the time. Most tagged barracuda were transient and would
often disappear from the array for months at a time, particularly in the summer where they were usually last detected on receivers
located in deeper shelf habitats, and then return at other times in the year. Habitat use across the footprint of the array
differed, with most detections occurring in coastal areas and comparatively fewer in deeper mosaic or shelf habitats. Linear
home range estimates revealed that some barracuda moved >12 km within a single day and are capable of migrating >100 km to
other islands in the Bahamian Archipelago. Our results provide some of the first telemetry data for this apex marine predatory
fish and the first reliable information on the residency and localized seasonal movements of adult great barracuda in the
coastal waters of the Western Atlantic. 相似文献
7.
Swordfish (Xiphias gladius) were tagged with satellite "pop-off" tags that release from the fish after a preprogrammed time, float to the sea surface, and transmit present position and archived temperature data. Swordfish were tagged on the "Charleston Bump," a topographic feature on the Blake Plateau east of South Carolina and Georgia. This feature is an important swordfishing ground and may be a spawning and nursery area. Swordfish were tagged in spring of 2000 to determine movements in relation to the Charleston Bump, and tags were programmed to pop off the fish at 30 days (n=10 tags), 60 days (n=10), and 90 days (n=9). Although four swordfish were found in the vicinity of the Charleston Bump up to 90 days after tagging, most moved considerable distances to the east and northeast and were subsequently located in association with offshore seamounts, submarine canyons of the Middle Atlantic Bight, and with thermal fronts of the northern wall of the Gulf Stream. The longest minimum (i.e., straight-line) distance tracked was 2,497 km, and maximum speed inferred from tracking was 34 km/day. Seawater temperature data archived by the tags reflected diel vertical migrations in swordfish. 相似文献
8.
The ocean sunfish (Mola mola) is typically considered to feed on gelatinous zooplankton, but reports in the literature describe various benthic organisms being found in their stomachs. This might reflect ontogenetic dietary shift, as little was known about the foraging habit of this species. We examined their foraging habits using dietary analyses in combination with a behavioral study in Iwate, Japan (39°22′N, 141°58′E) from 2009 to 2010. Our stomach content analyses (n = 17, 31–250 cm total length) suggested that small sunfish (<50 cm) feed on benthic crustaceans, but large sunfish (>200 cm) feed on jellyfish. Larger sunfish showed higher values of both carbon and nitrogen stable isotope ratios. Deployment of accelerometers and animal-borne cameras on small sunfish in July (49–58 cm, n = 5) suggested their possibility of feeding, while they stayed near the seabed. This indicates that small sunfish might feed on benthic preys. Deployment of accelero-magnetometers on large sunfish in July (84–164 cm, n = 4) clarified that the large sunfish in July swam back and forth between the surface and deep water (>100 m). Temporary decelerations, which were considered to be associated with feeding of planktonic prey, were observed in deep water. Whereas deployment of accelero-magnetometers on large sunfish in November (105 cm, n = 3) showed several bursts, they swam within the mixed layer (0–100 m), which might be associated with chasing of rapid prey. These results suggest that ocean sunfish have heterogeneous diets depending on their body size and possibly season. 相似文献
9.
Satellite tracking reveals a dichotomy in migration strategies among juvenile loggerhead turtles in the Northwest Atlantic 总被引:2,自引:2,他引:0
Katherine L. Mansfield Vincent S. Saba John A. Keinath John A. Musick 《Marine Biology》2009,156(12):2555-2570
Few data are available on the movements and behavior of immature Atlantic loggerhead sea turtles (Caretta caretta) from their seasonal neritic foraging grounds within the western north Atlantic. These waters provide developmental habitat
for loggerheads originating from several western Atlantic nesting stocks. We examined the long-term movements of 23 immature
loggerheads (16 wild-caught and seven headstart turtles) characterizing their seasonal distribution, habitat use, site fidelity,
and the oceanographic conditions encountered during their migrations. We identified two movement strategies: (1) a seasonal
shelf-constrained north–south migratory pattern; and (2) a year-round oceanic dispersal strategy where turtles travel in the
Gulf Stream to the North Atlantic and their northern dispersal is limited by the 10–15°C isotherm. When sea surface temperatures
dropped below 20°C, neritic turtles began a migration south of Cape Hatteras, North Carolina (USA) where they established
fidelity to the waters between North Carolina’s Outer Banks and the western edge of the Gulf Stream along outer continental
shelf. Two turtles traveled as far south as Florida. Several turtles returned to their seasonal foraging grounds during subsequent
summers. Northern movements were associated with both increased sea surface temperature (>21°C) and increased primary productivity.
Our results indicate strong seasonal and interannual philopatry to the waters of Virginia (summer foraging habitat) and North
Carolina (winter habitat). We suggest that the waters of Virginia and North Carolina provide important seasonal habitat and
serve as a seasonal migratory pathway for immature loggerhead sea turtles. North Carolina’s Cape Hatteras acts as a seasonal
“migratory bottleneck” for this species; special management consideration should be given to this region. Six turtles spent
time farther from the continental shelf. Three entered the Gulf Stream near Cape Hatteras, traveling in the current to the
northwest Atlantic. Two of these turtles remained within an oceanic habitat from 1 to 3 years and were associated with mesoscale
features and frontal systems. The ability of large benthic subadults to resume an oceanic lifestyle for extended periods indicates
plasticity in habitat use and migratory strategies. Therefore, traditional life history models for loggerhead sea turtles
should be reevaluated. 相似文献
10.
Mitochondrial DNA and electronic tracking reveal population structure of Atlantic bluefin tuna (Thunnus thynnus) 总被引:1,自引:0,他引:1
Population subdivision was examined in Atlantic bluefin tuna (Thunnus thynnus) through sequencing of the control region of the mitochondrial genome. A total of 178 samples from the spawning grounds in
the Gulf of Mexico, Bahamas and Mediterranean Sea were analyzed. Among the samples from these locations were 36 electronically
tagged bluefin tuna that were tagged in the North Atlantic and subsequently traveled to one of these known spawning grounds
during the spawning season. Bluefin tuna populations from the Gulf of Mexico and the Mediterranean Sea were found to be genetically
distinct based on Φst, and sequence nearest neighbor analyses, showing that these two major spawning areas support independent stocks. Sequence
nearest neighbor analysis indicated significant population subdivision among the Gulf of Mexico, western Mediterranean and
eastern Mediterranean Sea. However, it was not possible to find significant pairwise differences between any sampling areas
when using all samples. If only samples that had a high likelihood of assignment to a specific spawning site were used (young
of the year, spawning adults), the differentiation increased among all sampling areas and the Western Mediterranean Sea was
distinct from the Eastern Mediterranean Sea and the Gulf of Mexico. It was not possible to distinguish samples from the Bahamas
from those collected at any of the other sampling sites. These data support tagging results that suggested distinctness of
the Gulf of Mexico, Eastern and Western Mediterranean Sea spawning areas. This level of stock differentiation is only possible
if Atlantic bluefin tuna show strong natal homing to individual spawning grounds. 相似文献
11.
The movements of nine harbour porpoises, Phocoena phocoena (L.), in the Bay of Fundy and Gulf of Maine were tracked using satellite telemetry. Transmitters were attached to the porpoises
in August 1994 and 1995 after they were captured near Grand Manan Island at the mouth of the Bay of Fundy. Tracking periods
ranged from 2 to 212 d (mean 50 ± 65 d). Porpoises exhibited a high degree of individual variation in movement patterns; five
moved out of the Bay of Fundy into the Gulf of Maine. The porpoise with the longest tracking period moved extensively throughout
the Gulf of Maine. These data suggest that seasonal movement patterns of individual harbour porpoises are discrete and are
not temporally coordinated migrations. Porpoises that moved out of the Bay of Fundy into the Gulf of Maine did so following
the 92 m isobath, which may represent an important movement corridor. The movement of porpoises from the Bay of Fundy into
the Gulf of Maine supports the hypothesis that harbour porpoises from these two regions comprise a single population at risk
of entanglement in both Canadian and US fisheries.
Received: 4 February 1997 / Accepted: 25 August 1997 相似文献
12.
Prevailing oceanographic processes, pelagic larvae, adult mobility, and large populations of many marine species often leads
to the assumption of wide-ranging populations. Applying this assumption to more localized populations can lead to inappropriate
conservation measures. The Pacific ocean perch (Sebastes alutus, POP) is economically and ecologically valuable, but little is known about its population structure and life history in Alaskan
waters. Fourteen microsatellite loci were used to characterize geographic structure and connectivity of POP collections (1999–2005)
sampled along the continental shelf break from Dixon Entrance to the Bering Sea. Despite opportunities for dispersal, there
was significant, geographically related genetic structure (F
ST = 0.0123, P < 10−5). Adults appear to belong to neighborhoods at geographic scales less than 400 km, and possibly as small as 70 km, which indicates
limited dispersal throughout their lives. The population structure observed has a finer geographic scale than current management,
which suggests that measures for POP fisheries conservation should be revisited. 相似文献
13.
14.
P. V. Hamilton 《Marine Biology》1978,46(1):49-58
The distribution of Littorina irrorata Say on a low-energy barrier beach on the northern Gulf of Mexico is described, and correlated with the presence of Spartina alterniflora and other plants in the upper intertidal zone. The movements of 66 individually tagged snails were followed in the S. alterniflora zone for an average of 226 days, during which time an average of 10.6 positions were recorded per snail. The snails travelled an average total path distance of at least 995 cm, but due to contorted paths, ended up an average resultant distance of only 399 cm away from their original positions. They moved an estimated resultant distance of approximately 20 to 25 cm per activity period. Despite a slight offshore movement during the fall and winter, the snails moved more parallel to the shoreline than perpendicular to it. 相似文献
15.
The upwelling systems along the coast of Morocco support some of the largest populations of sardine (Sardina pilchardus) in the world. Although these populations provide a base for a substantial fishing industry, virtually nothing is known about
the genetic stock structure of this fish. Samples (n = 346), collected from seven sites along the Atlantic coast and in the Alboran Sea, were examined for exon-primed intron-crossing
PCR (EPIC-PCR) polymorphism. Two markers, CaM-4 and Ops-1, had 6 and 9 alleles, respectively, after the pooling of gel fragments
into 5 bp length classes, Correspondence analysis and the distribution of F
st among samples indicated that Moroccan populations were divided into two groups with F
st = 0.034 (P < 0.05) across the Gibraltar Strait. Populations along the Atlantic coast of Morocco comprise one genetic unit, except for
a weak genetic boundary south of Cape Ghir and the peculiar behavior of the Safi sample would indicate a genetic drift. Complex
ocean hydrodynamics around Gibraltar Strait and across Cape Ghir, likely, contributes to these genetic isolations. These results
point out the usefulness of population genetic studies in stock management for sardine populations that may be particularly
vulnerable to overexploitation especially during upwelling intensity shifts. 相似文献
16.
The Atlantic surfclam, Spisula solidissima (Dillwyn), is broadly distributed in sandy sediments of the western North Atlantic between the Gulf of St. Lawrence and the Gulf of Mexico. In the United States, a substantial commercial fishery between Long Island and Cape Hatteras harvests offshore populations of one subspecies, S. s. solidissima. A smaller coastal form, S. s. similis Say (also known as S. s. raveneli Conrad), has a partially sympatric geographic distribution, but differs in several life-history characteristics. DNA sequence variation in mitochondrial cytochrome oxidase I (COI) and in introns at two nuclear calmodulin loci was examined to measure genetic divergence between the two subspecies and to test for population structure among populations of S. s. solidissima. Surfclams were collected from seven localities between 1994 and 2001. Based on both mitochondrial and nuclear DNA variation, the two subspecies of S. solidissima are reciprocally monophyletic, with a net COI divergence of 13.9%, indicating long-term reproductive isolation. The only significant differentiation among populations of S. s. solidissima (based on an AMOVA analysis of COI sequences) was between the Gulf of St. Lawrence and more southerly populations. A long internal branch in the S. s. solidissima genealogy coupled with low haplotype diversity in the northern-most population suggests that populations north and south of Nova Scotia have been isolated from each other in the past, with gene exchange more recently. Populations of S. s. similis from Atlantic and Gulf of Mexico coasts had a net COI divergence of 9.2%. Thus, diversification of Spisula spp. clams in the western North Atlantic involved an early adaptive divergence between coastal and offshore forms, with later barriers to dispersal emerging in the offshore form from north to south and in the coastal form between Atlantic and Gulf of Mexico populations. 相似文献
17.
Population differentiation of the Atlantic spotted dolphin (Stenella frontalis) in the western North Atlantic, including the Gulf of Mexico 总被引:4,自引:2,他引:2
Information about the genetic population structure of the Atlantic spotted dolphin [Stenella frontalis (G. Cuvier 1829)] in the western North Atlantic would greatly improve conservation and management of this species in USA
waters. To this end, mitochondrial control region sequences and five nuclear microsatellite loci were used to test for genetic
differentiation of Atlantic spotted dolphins in the western North Atlantic, including the Gulf of Mexico (n=199). Skin tissue samples were collected from 1994–2000. Significant heterozygote deficiencies in three microsatellite loci
within samples collected off the eastern USA coast prompted investigation of a possible Wahlund effect, resulting in evidence
for previously unsuspected population subdivision in this region. In subsequent analyses including three putative populations,
two in the western North Atlantic (n=38, n=85) and one in the Gulf of Mexico (n=76), significant genetic differentiation was detected for both nuclear DNA (R
ST=0.096, P≤0.0001) and mitochondrial DNA (Φ
ST=0.215, P≤0.0001), as well as for all pair-wise population comparisons for both markers. This genetic evidence for population differentiation
coupled to known biogeographic transition zones at Cape Hatteras, North Carolina and Cape Canaveral, Florida, USA, evidence
of female philopatry, and preliminary support for significant genetic differences between previously documented morphotypes
of Atlantic spotted dolphins in coastal and offshore waters all indicate that the biology and life history of this species
is more complex than previously assumed. Assumptions of large, panmictic populations might not be accurate in other areas
where S. frontalis is continuously distributed (e.g., eastern Atlantic), and could have a detrimental effect on long-term viability and maintenance
of genetic diversity in this species in regions where incidental human-induced mortality occurs.
相似文献
Lara D. AdamsEmail: |
18.
Blue mussels in the genus Mytilus first arrived in the Atlantic Ocean from the Pacific during the Pliocene, following the opening of the Bering Strait. Repeated
periods of glaciation throughout the Pleistocene led to re-isolation of the two ocean basins and the allopatric divergence
of Mytilus edulis in the Atlantic and M. trossulus in the Pacific. Mytilus trossulus has subsequently colonized the northwest Atlantic (NW Atlantic) so that the two species are presently sympatric and hybridize
throughout much of the Canadian Maritimes and the Gulf of Maine. To estimate when M. trossulus arrived in the NW Atlantic, we have examined sequence variation within a portion of the female mtDNA lineage large untranslated
region (F-LUR) for 156 mussels sampled from three Pacific and eleven Atlantic populations of M. trossulus. Although we found no evidence of reciprocal monophyly for Pacific and NW Atlantic M. trossulus, limited gene flow between ocean basins has led to the divergence of unique sequence clades within each ocean basin. In contrast,
relative genetic homogeneity indicates high levels of gene flow within each basin. Coalescence-based analysis of the F-LUR
sequences suggests that M. trossulus recolonized the NW Atlantic from the northeast Pacific subsequent to a demographic expansion in the Pacific that occurred
~96,000 years before present (ybp). Estimates of timing of divergence for Pacific and NW Atlantic populations and the time
since expansion among NW Atlantic sequence clades indicate that M. trossulus arrived in the NW Atlantic more recently, between 20,000 and 46,000 ybp. Given that these estimates overlap with the dates
of peak ice in the NW Atlantic during the last glacial maximum (LGM, ~18,000–21,000 ybp), we suggest that colonization of
the NW Atlantic by M. trossulus occurred during, but more likely just subsequent to, the LGM and was followed by rapid temporal and spatial expansion in
the region. 相似文献
19.
Lane snappers (Lutjanus synagris), sampled from eight localities in the northern Gulf of Mexico (Gulf) and one locality along the Atlantic coast of Florida,
were assayed for allelic variation at 14 nuclear-encoded microsatellites and for sequence variation in a 590 base-pair fragment
of the mitochondrially encoded ND-4 gene (mtDNA). Significant heterogeneity among the nine localities in both microsatellite
allele and genotype distributions and mtDNA haplotype distributions was indicated by exact tests and by analysis of molecular
variance (AMOVA). Exact tests between pairs of localities and spatial analysis of molecular variance (SAMOVA) for both microsatellites
and mtDNA revealed two genetically distinct groups: a Western Group that included six localities from the northwestern and
northcentral Gulf and an Eastern Group that included three localities, one from the west coast of Florida, one from the Florida
Keys, and one from the east (Atlantic) coast of Florida. The between-groups component of molecular variance was significant
for both microsatellites (Φ
CT = 0.016, P = 0.009) and mtDNA (Φ
CT = 0.208, P = 0.010). Exact tests between pairs of localities within each group and spatial autocorrelation analysis did not reveal genetic
heterogeneity or an isolation-by-distance effect among localities within either group. MtDNA haplotype diversity was significantly
less (P < 0.0001) in the Western Group than in the Eastern Group; microsatellite allelic richness and gene diversity also were significantly
less in the Western Group (P = 0.015 and 0.013, respectively). The difference in genetic variability between the two groups may reflect reduced effective
population size in the Western Group and/or asymmetric rates of genetic migration. The relative difference in variability
between the two groups was substantially greater in mtDNA and may reflect one or more mtDNA selective sweeps; tests of neutrality
of the mtDNA data were consistent with this possibility. Bayesian analysis of genetic demography indicated that both groups
have experienced a historical decline in effective population size, with the decline being greater in the Western Group. Maximum-likelihood
analysis of microsatellite data indicated significant asymmetry in average, long-term migration rates between the two groups,
with roughly twofold greater migration from the Western Group to the Eastern Group. The difference in mtDNA variability and
the order-of-magnitude difference in genetic divergence between mtDNA and microsatellites may reflect different demographic
events affecting mtDNA disproportionately and/or a sexual and/or spatial bias in gene flow and dispersal. The spatial discontinuity
among lane snappers in the region corresponds to a known zone of vicariance in other marine species. The evidence of two genetically
distinct groupings (stocks) has implications for management of lane snapper resources in the northern Gulf. 相似文献
20.
The loliginid squids Loligo pealei LeSueur and L. plei Blaineville (both recently proposed for reclassification as Doryteuthis) are commercially important, similar in appearance, and sympatric throughout much of the northwestern Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea. To investigate possible cryptic speciation and population structure, we examined samples (collected from 1995 to 1997) of both species for restriction fragment length polymorphisms (RFLPs) in PCR products of the mitochondrial gene cytochrome c oxidase (subunit I). RFLP haplotypes were further characterized by direct sequencing. In North American waters, cryptic speciation was rejected by the far greater nucleotide sequence divergence between species (~14%) versus within species (<1%). Each species displayed about a dozen RFLP haplotypes, but only three of their respective haplotypes were found among 90% of L. pealei specimens (n=356) and 97% of L. plei specimens (n=431). For L. pealei, a genetic break existed between the northern Gulf of Mexico and the Atlantic Ocean; among sample units within each population, gene flow was consistent with panmixia. The phylogeography of L. pealei is likely a consequence of the eastward currents of the Florida Straits, the elevated temperatures of those surface waters, and the restriction of this species to the continental shelf. For L. plei, a genetic break existed between longitudes 88°W and 89°W, with the northwestern Gulf of Mexico and the northeastern Gulf-Atlantic Ocean comprising separate populations; among sample units within each population, gene flow fit an isolation-by-distance model. If the genetic break found for L. plei represents resident populations separated by nearshore physical parameters (e.g. effects of the Mississippi River and the sediment boundary at longitude 88°W), the lack of structure within the Gulf for L. pealei might be due to its distribution farther from shore. However, the two populations of L. plei probably represent annual recolonization from the southwestern Gulf of Mexico and from the eastern Caribbean Sea, whereas the populations of L. pealei probably are permanent residents within their respective regions. 相似文献