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Fishery Bulletin 115(4) 
Atlantic Ocean cobia stocks needs to be more accurate¬ 
ly defined (SEDAR 1 ) to aid future assessments. 
Estimates of mortality from tagging programs can 
improve stock assessment efforts by providing an al¬ 
ternative estimate of natural, fishing, or total mortal¬ 
ity independent of the stock assessment model (Wood 
and Cadrin, 2013; Kerns et al., 2015). Several types of 
tag-recapture methods exist (Pine et al., 2003), and for 
cooperative tagging programs, tag-recovery models are 
used to estimate survivorship and the probability of 
tag recovery (Brownie et al., 1985). Tag-recovery meth¬ 
ods for estimating mortality have been used for yel- 
lowtail flounder (Limanda ferruginea) in New England 
(Wood and Cadrin, 2013), walleye (Sander vitreus) in 
Lake Erie (Vandergoot and Brenden, 2014) and paddle- 
fish (Polyodon spathula) in a South Dakota lake (Pierce 
et al., 2015). Estimates of mortality derived from tag- 
recapture data can be used to corroborate estimates de¬ 
rived with age-structured models or life-history-based 
approaches (Then et al., 2015). 
The goals for this study were to use data from a 
27-year cooperative tagging program to describe the 
growth, mortality, and movement of cobia in the Gulf 
of Mexico and South Atlantic Ocean. Specifically, we 1) 
describe the length-at-age relationship of cobia using 
a suite of nonlinear length-at-age models fitted to the 
tag-recapture data, 2) report cobia movement between 
the Gulf of Mexico and South Atlantic Ocean, 3) de¬ 
scribe the spatial and seasonal distribution of cobia in 
the Gulf of Mexico, and 4) estimate annual instanta¬ 
neous total mortality (Z), using a suite of tag-recovery 
models. The results of this study will help fill existing 
information gaps and provide critical information to 
support the sustainable management of cobia in the 
Gulf of Mexico and South Atlantic Ocean. 
Materials and methods 
Tagging and recapture 
The Sport Fish Tag and Release Program (Hendon 
and Franks 5 ) began in 1988 as a cooperative tagging 
program during which volunteer recreational anglers 
tagged cobia with 10-cm plastic-tipped dart tags (Hall- 
print Pty. Ltd. 10 , Hindmarsh Valley, Australia). An¬ 
glers participating in the program received tagging 
kits containing tags with unique numerical identifiers, 
data reporting cards, a tag applicator, and a booklet 
containing tagging instructions. Tagging guidelines 
provided with the tagging kit instructed anglers on 
the proper tag-release procedures to enhance tag re¬ 
tention and ensure safe handling of tagged fish before 
release. At the time of tagging, volunteer anglers re¬ 
corded information on the approximate tagging loca¬ 
tion, date, the length of the fish (typically measured 
“Mention of trade names or commercial companies is for iden¬ 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
as EL in inches), and a qualitative description of fish 
condition at time of release. Anglers then mailed the 
tag-reporting card to the Gulf Coast Research Labora¬ 
tory where the tagging data were recorded and entered 
into an electronic tag-recapture database. If a fish was 
recaptured, anglers were asked to report their catch by 
email, mail, or phone to the Gulf Coast Research Labo¬ 
ratory and provide information on the date of capture, 
location of catch, length-at-recapture, and whether the 
fish was retained or released, and if released, to pro¬ 
vide a qualitative report on its condition. 
The cooperative tagging program was advertised 
broadly and frequently. Posters describing the program 
were distributed to bait and tackle shops, boat launch¬ 
es, fishing tournaments, and sporting goods stores. The 
program was also occasionally reported in the media 
through newspaper articles, local television interviews, 
and regional fishing magazines. No financial incentives 
were offered during the program duration, but anglers 
who tagged numerous cobia in a given year were given 
informal recognition in the media and regional fishing 
magazines. Often, anglers who recaptured a tagged co¬ 
bia became interested in obtaining a cobia tagging kit. 
Growth 
To describe the length-at-age relationship, 3 nonlinear 
length-at-age models were fitted to the cobia tag-recap¬ 
ture informatiion. Multimodel approaches for describ¬ 
ing growth can help reduce model misspecification and 
can help identify the most appropriate length-at-age 
model to use for a particular species (Katsanevakis, 
2006). Each of the 3 models used were reparameter¬ 
ized versions of commonly used length-at-age models, 
reformulated to fit the observed change in length in¬ 
formation over the time that tagged fish were at large. 
Before model fittings, if a length-at-tagging or recap¬ 
ture was reported as total length (TL), it was converted 
to FL by using a TL-to-FL linear model conversion. The 
first model used was the Fabens (1965) von Bertalanffy 
growth function (VBGF). The Fabens model is 
AL = (L m - L t ) (1 - e _kAt ), (1) 
where L = the mean asymptotic length (millimeters in 
FL); and 
k = the growth coefficient (per year). 
The observed data used in the model are AL, the 
change in length (millimeters in FL), and At, the time 
between tagging and recapture events (in years). 
The second model used to describe the length-at-age 
relationship of cobia was a reparameterized Gompertz 
model (Troynikov et al., 1998): 
AL = Loo (A) exp< - kAt) _ L _ ; (2) 
whereL = again the mean asymptotic FL (millimeters 
in FL); and 
k = the decrease in growth increment (per year) 
as length increases. 
The observed data used in the model are At (years), the 
