Dippold et al.: Growth, mortality, and movement of Rachycentron canadum 
461 
The species has only recently been assessed under the 
Southeast Data, Assessment, and Review (SEDAR) pro¬ 
cess (SEDAR 1 ) and the most recent SEDAR assessment 
involved a separate assessment of the Gulf of Mexico 
and South Atlantic Ocean stocks. 
In the most recent SEDAR assessments, several in¬ 
formation gaps were identified which limited the deter¬ 
mination of the status of both the Gulf of Mexico and 
South Atlantic Ocean cobia stocks. Specifically, there 
was an insufficient amount of information available 
to accurately determine stock boundaries, and further 
descriptions of life-history characteristics and popula¬ 
tion dynamics were needed. Towards this end, we used 
information from the Sport Fish Tag and Release Pro¬ 
gram of the University of Southern Mississippi Gulf 
Coast Research Laboratory (Hendon and Franks 5 ) to 
investigate the growth, movement, and mortality of 
cobia in the Gulf of Mexico and South Atlantic Ocean 
in order to fill critical information gaps regarding life- 
history and population dynamics for this species, as 
well as to corroborate existing life-history descriptions 
by using an alternative source of information. We focus 
on the stocks of the Gulf of Mexico and South Atlantic 
Ocean, given that stocks of these areas were the focus 
of a cooperative tagging program. 
Cooperative tagging programs can provide valu¬ 
able information at the individual and population lev¬ 
els and on the fishery dynamics of recreationally and 
commercially harvested species (Wood and Cadrin, 
2013). Cooperative tagging programs have been imple¬ 
mented for several groups of marine fishes, such as 
dolphinfish, sailfish, marlin, and sharks, and informa¬ 
tion from these programs has provided invaluable and 
previously unreported information on the movement 
and biology of these taxa (Jones and Prince, 1998; 
Kohler et al., 1998; Ortiz et al., 2003). For example, 
cooperative tagging programs have been used to esti¬ 
mate mortality (Pine et al., 2003; Wood and Cadrin, 
2013), describe individual growth dynamics (Simpfen- 
dorfer, 2000; Dippold et al., 2016), and show move¬ 
ment patterns (Hendon et al., 2002; Queiroz et al., 
2005; Hussey et al., 2009). In this study we used simi¬ 
lar methods with a 27-year cooperative tagging data 
set (Hendon and Franks 5 ). Although other cobia tag¬ 
ging programs exist in the Gulf of Mexico and South 
Atlantic Ocean (Shaffer and Nakamura, 1989; Burns 
and Neidig 6 ; Wiggers 7 ; Orbesen 8 ), to our knowledge 
5 Hendon, J. R. and J. S. Franks. 2010. Sport fish tag 
and release in Mississippi coastal waters and the adjacent 
Gulf of Mexico. Gulf Coast Res. Lab. Tech. Rep. F-132, 34 
p. [Available from Gulf Coast Research Laboratory, 703 
East Beach Dr., Ocean Springs, MS 39564.] 
6 Burns, K. M., and C. L. Neidig. 1992. Cobia ( Rachycen¬ 
tron canadum) amberjack (Seriola drumerili) and dolphin 
(Corypheana hippurus ) migration and life history study off 
the southwest coast of Florida. Mote Mar. Lab. Tech. Rep. 
267, 58 p. [Available from website.] 
1 Wiggers, R. K. 2010. South Carolina marine game fish 
tagging program 1978-2009. South Carolina Dep. Nat. Re¬ 
sour., Charleston, SC. [Available from website.] 
8 Orbesen, E. 2012. Constituent based tagging of cobia in 
the Sport Fish Tag and Release Program is the most 
comprehensive. 
Individual growth has previously been described in 
cobia by using otolith- and scale- derived age estimates, 
and annuli formation has been validated by using mar¬ 
ginal increment analysis (Richards, 1967; Thompson et 
al. 9 ; Smith, 1995; Franks et al., 1999). However, the 
use of marginal increment analysis as a method for 
age validation can be problematic because of the diffi¬ 
culty in interpreting the otolith margin and because of 
the need to validate annuli formation across the entire 
lifespan of a species (Campana, 2001). Age corrobora¬ 
tion, or the estimation of growth parameters with al¬ 
ternative methods, is used to increase confidence in 
growth model parameter estimates (Campana, 2001). 
Specifically, tag-recapture information for estimating 
growth parameters has been used as an alternative 
method for describing the length-at-age relationship in 
several marine species (Natanson et al., 1999; Dippold 
et al., 2016). No age corroboration method has been 
evaluated for cobia, and because cobia are assessed by 
using a statistical catch-at-age model (SEDAR 1 ), ac¬ 
curate descriptions of length-at-age are needed to es¬ 
timate age-specific vital rates such as instantaneous 
fishing-induced [also termed “fishing mortality] and 
natural mortality. In this study, we use a suite of non¬ 
linear length-at-age models to analyze tag-recapture 
data in order to corroborate existing estimates of the 
length-at-age relationship of cobia. 
In addition to describing the length-at-age relation¬ 
ship, information from tagging programs can be used 
to describe general and seasonal movement and dis¬ 
tribution patterns and to determine stock boundaries 
(Wood and Cadrin, 2013; Kneebone et al., 2014). The 
results of small-scale cooperative tagging of cobia have 
suggested that some individuals migrate long distances 
and indicate seasonal movement patterns (Shaffer and 
Nakamura, 1989; Burns and Neidig 6 ; Wiggers 7 ; Orbe¬ 
sen 8 ). However, in these studies, either relatively few 
individuals were tagged, only a small portion of tagged 
individuals was recaptured, the study occurred over a 
small sampling period, or long-distance movement was 
reported for only a few individuals. The determination 
of cobia stock boundaries is critical given the reported 
movements of this species between ocean basins. Ge¬ 
netic analysis to determine cobia stock discrimination 
has been evaluated for the Atlantic Ocean but has 
not been evaluated for the Gulf of Mexico (Darden et 
al., 2014). Because of the lack of resolution regarding 
seasonal movement patterns and the degree of mixing 
between the Gulf of Mexico and Atlantic Ocean cobia 
populations from both tagging and genetic studies, the 
current stock boundary between the Gulf of Mexico and 
the Atlantic and Gulf of Mexico waters. Southeast Data 
Assessment and Review SEDAR28-DW13, 10 p. [Available 
from website.] 
9 Thompson, B. A., C. A. Wilson, J. H. Render, and M. Beasley. 
1992. Age, growth, and reproductive biology of greater am¬ 
berjack and cobia from Louisiana waters, 55 p. Louisiana 
State University, Baton Rouge, LA. 
