Perkinson et a!.: Evaluation of the stock structure of Rachycentron canadum in the southeastern United States 
231 
that Cape Canaveral falls within this transitional area, 
genetic and tag-recapture data for northern Florida and 
Georgia are limited, making it difficult to determine how 
far this transition extends to the north. 
The area around Cape Canaveral is a well-studied 
phylogeographic break for many species (Burton, 1998; 
Hellberg et al., 2002). Species that either terminate their 
southern range or show a divergence in genetics in this 
area include the Eastern oyster (Crassostrea virginica) 
(Reeb and Avise, 1990), Atlantic menhaden ( Brevoor- 
tia tyrannus ) and black sea bass ( Centropristis striata ) 
(Bowen and Avise, 1990), and American horseshoe crab 
(Limulus polyphemus) and oyster toadfish (Opsanus tau) 
(Avise, 1992). The region marks the transition from a 
temperate to a subtropical climate where the Gulf Stream 
diverges from the coastline (Avise, 1992), with potential 
implications for the distribution of eggs and larvae. Dif¬ 
ferences in water temperature between the areas north 
and south of Cape Canaveral may also have an impact on 
the migratory behavior of cobia. Oceanographic tempera¬ 
ture data from the NOAA National Data Buoy Center 
indicate that the coastal waters at and just north of Cape 
Canaveral are the southernmost location along the U.S. 
Atlantic coast where coastal mean water temperatures 
routinely fall below 20°C during winter. The waters off¬ 
shore or south of Cape Canaveral through the Florida 
Keys typically remain above 20°C throughout the year. 
These moderate winter water temperatures may explain 
why some cobia in these waters do not appear to make 
long migrations and may be found there year-round. By 
contrast, coastal waters north of Cape Canaveral regu¬ 
larly fall below 20°C and result in the movement of cobia 
into more southerly waters, deeper waters, or a combina¬ 
tion of both. 
The transitional area occurring within the range of 
Cape Canaveral to northern Georgia appears to serve as 
a major division between GOM and western North Atlan¬ 
tic Ocean stocks. The complete population structure and 
migratory patterns of GOM and Atlantic Ocean cobia is 
likely more complex. Tag-recapture data indicate multiple 
migratory behaviors and geographic partitioning of cobia 
in the Atlantic Ocean group underscored by the lack of 
exchange between cobia tagged in Virginia or North Car¬ 
olina and cobia tagged in South Carolina. Hendon and 
Franks 3 suggested multiple migratory patterns from cobia 
tagged in the GOM as well. These complicated migra¬ 
tory patterns are further supported by genetic analysis. 
Darden et al. (2014) found evidence of distinct population 
segments within the western North Atlantic Ocean stock. 
Although our study found no genetic differences through¬ 
out the GOM stock, increased sample sizes in the Flor¬ 
ida Keys and northern GOM locations could potentially 
provide greater resolution into the genetic population 
structure of cobia in these areas. Current projects that 
use acoustic and satellite telemetry, as well as additional 
genetic and conventional tagging data, when evaluated in 
concert, will increase our understanding of cobia structure 
on a regional level and benefit the assessment and man¬ 
agement process moving forward. 
Acknowledgments 
We wish to thank the late K. Burns whose tagging data 
was integral to these analyses and the Mote Marine Lab¬ 
oratory for allowing their inclusion. We also thank the 
Hilton Head Reef Foundation, S. Poland at the North 
Carolina Division of Marine Fisheries, contributing 
anglers, and the NOAA Hollings Marine Laboratory. 
Funding for the analyses included South Carolina Salt¬ 
water Recreational License Funds and NOAA CRP project 
NA15NMF4540105. This manuscript represents SCDNR 
MRRI contribution number 807. 
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