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Fishery Bulletin 11 5(4) 
erative tagging programs, our estimates are still a rel¬ 
evant method of corroboration given that sex-combined 
length-at-age models are used in current assessment 
models. However, in the future, we recommend that 
sex of recaptured individuals be reported if available. 
This information could be collected at fishing tourna¬ 
ments where scientists are often on site gathering bio¬ 
logical information, or incentives could be offered to 
bring carcasses to scientists for sex identification. 
As with the description of individual growth dynam¬ 
ics, we provide an independent estimate of Z that can 
be used to corroborate mortality values estimated by 
using an age-structured stock assessment model. In 
most stock assessment frameworks, natural and fishing 
mortality rates are difficult to estimate and are often 
obtained by theoretical estimates (Then et ah, 2015). 
Tag-recovery models do not require the use of a spe¬ 
cific natural mortality function to estimate Z, and thus 
avoid some potential biases in describing the natural 
mortality component of Z. In this study, we estimated 
annual Z by using tag-recovery models (0.59/year [95% 
Cl: 0.55-0.63]). In the 2013 stock assessment of cobia 
in the Gulf of Mexico, the current estimated annual 
total mortality (the sum of the geometric mean fishing 
mortality and natural mortality) was 0.62/year. During 
the period included in the assessment, fishing mortal¬ 
ity varied annually but has remained relatively stable, 
especially in the most recent years of the assessment. 
Our estimate of Z is similar to those values estimated 
in the stock assessment model. We included recaptures 
from both the Gulf of Mexico and a limited number 
from the South Atlantic Ocean in our analysis (to ac¬ 
count for individuals tagged in Gulf of Mexico and har¬ 
vest in South Atlantic Ocean) and recognize that our 
estimate is by necessity stock-aggregated. 
Clarification of the stock boundary along the Atlan¬ 
tic coast of Florida was considered a research need of 
high importance by assessment scientists (SEDAR 1 ), 
and cooperative research efforts can contribute to this 
effort (Lucy and Davy, 2000). This study confirms the 
presence of large scale movements of individual cobia 
within the Gulf of Mexico and into the South Atlan¬ 
tic Ocean. The scale of our work, in terms of both the 
number of individuals tagged and the spatial coverage, 
is greater than that of previous studies and strength¬ 
ens the descriptions of cobia movement. Previously, 
Burns and Neidig 6 tagged 171 cobia from 1990 to 1992, 
recaptured 10 individuals and suggested both seasonal 
northern and southern movements and seasonal on- 
shore-offshore movements. Orbesen 8 synthesized coop¬ 
erative tagging information collected from the NOAA 
Southeast Fisheries Science Center, information that 
included 1510 tagged cobia and 148 recaptures over 58 
years. Using that synthesized recapture information 
and the 6 defined geographic zones (as opposed to the 
7 zones defined in our study), Orbesen 8 observed mix¬ 
ing among all 6 zones, and that more mixing occurred 
between the Keys and the Gulf zones than between any 
other 2 zones. For the South Carolina Marine Game 
Fish Tagging Program, 1066 cobia were tagged be¬ 
tween 1986 and 2009 and 201 individuals were recap¬ 
tured (Wiggers 7 ). On the basis of the reported tagging 
and recapture locations, most fish showed site fidelity, 
although some mixing between the Gulf of Mexico and 
South Atlantic Ocean was observed. Other studies have 
also reported mixing between the Gulf of Mexico and 
South Atlantic Ocean on the basis of a few recaptured 
individuals (Shaffer and Nakamura, 1989). Most of 
these tagging studies had a small number of recap¬ 
tured individuals or were conducted for a relatively 
short time period (or were a combination of both). Be¬ 
cause of the observed long-distance movements and 
the current problems with identification of the stock 
boundary between the Gulf of Mexico and South At¬ 
lantic Ocean stocks, the relatively greater number of 
tagged and recaptured individuals used in this study 
and the duration of the tagging program allow stron¬ 
ger inferences of seasonal and long-distance movement 
patterns of cobia in the Gulf of Mexico and South At¬ 
lantic Ocean. 
The results of our work indicate that there is an 
evident seasonal distribution pattern: individuals are 
more frequently recaptured in the Florida Keys during 
the winter and in the northern Gulf of Mexico during 
the summer. Currently, the South Atlantic Ocean and 
Gulf of Mexico stocks are divided at the Florida-Geor- 
gia state line (SEDAR 1 ). The boundary is determined 
on the basis of ease of management; however, there 
is little evidence from genetic or tagging work to con¬ 
firm the validity of this designation (SEDAR 1 ). Some 
genetic evidence indicates homogeny among offshore 
cobia along the Atlantic coast and some genetic distinc¬ 
tion among inshore aggregations; however, no similar 
genetic information on population structure and parti¬ 
tioning exists for cobia in the Gulf of Mexico (Darden 
et al., 2014). We find that of the individuals tagged in 
the Gulf of Mexico zones, no more than 11% of recap¬ 
tures of individuals tagged in a given Gulf of Mexico 
zone occurred in the South Atlantic Ocean. Additional¬ 
ly, of the individuals tagged in the Atlantic Ocean and 
subsequently recaptured, only 14% were recaptured in 
the Florida Keys, and recapture rates in the other Gulf 
of Mexico zones ranged from 0 to 5%. These results 
suggest that the Florida Keys may be a mixing zone 
and that the current stock boundary at the Florida 
Georgia state line may be inappropriate. However, we 
did not incorporate differences in fishing and sampling 
effort into our modeling approaches and we note that 
seasonal differences in fishing effort between zones 
may bias our descriptions of movement and seasonal 
recapture patterns. Additionally, because of the scope 
of the cooperative tagging program, we were limited to 
providing descriptions of movement and distribution to 
the Gulf of Mexico and South Atlantic Ocean. 
The results of our research suggest a seasonal pat¬ 
tern of distribution of cobia in the Gulf of Mexico. Spe¬ 
cifically, the results of the loglinear analysis presented 
here indicate that the Florida Keys may be a winter¬ 
ing ground for cobia and that individuals may exhibit 
northward movement toward the Florida panhandle 
