Direct validation of ages determined 
for adult black drum, Pogonias cromis, 
in east-central Florida, with notes on 
black drum migration 
Michael D. Murphy 
Florida Marine Research Institute, Department of Environmental Protection 
1 00 Eighth Avenue 
St- Petersburg, Florida 33701-5095 
E-mail address: murphy_m@harpo. dep.state.fi. us 
Douglas H. Adams 
Derek SVL Tremain 
Florida Marine Research Institute, Department of Environmental Protection 
I 220 Prospect Avenue, Suite 285 
Melbourne, Florida 32901 
Brent L Winner 
Florida Marine Research Institute, Department of Environmental Protection 
1 00 Eighth Avenue 
St. Petersburg, Florida 33701-5095 
Findings from indirect age valida- 
tion studies, in which marginal in- 
crements in black drum, Pogonias 
cromis, otolith sections were exam- 
ined, indicate that the number of 
opaque bands observed in otoliths 
is a measure of the true age in years 
of black drum (Murphy and Taylor, 
1989; Beckman et al., 1990; Beck- 
man et al. 1 ). However, validation 
studies of scale-determined ages 
have indicated that more than one 
mark is deposited on black drum 
scales each year after they reach 
about age four (Richards, 1973; 
Cornelius, 1984). In addition, evi- 
dence from an analysis of the mar- 
ginal increments for a related 
sciaenid, the croaker Micropogonias 
opercularis, has indicated that more 
than one opaque band was depos- 
ited on its otoliths each year (Hai- 
movici, 1977). 
Unlike indirect validation stud- 
ies which provide estimates of the 
periodicity of annulus formation for 
a sample of fish, mark-recapture 
studies provide proof of the accu- 
racy of an age determination tech- 
nique for an individual fish during 
the period of time between mark- 
ing and recapture (Beamish and 
McFarlane, 1983). This direct tech- 
nique has been used to validate 
ages for a variety of species, includ- 
ing red drum, Sciaenops ocellatus 
(Murphy and Taylor, 1991; Ross et 
al., 1995); snapper, Pagrus auratus 
(Francis et al., 1992); sablefish, 
Anoplopoma fimbria (McFarlane 
and Beamish, 1995); and the tropi- 
cal parrotfish Scarus schlegeli (Lou, 
1992). Because mark-recapture 
studies provide information on the 
validity of age marks formed since 
the mark was applied, they cannot 
be extrapolated to imply the valid- 
ity of younger ages (Francis, 1995). 
In assessing the status of black 
drum stocks, accurate age determi- 
nation is especially critical. These 
fish are suspected to live to about 
60 years old, and the large fisher- 
ies that they have supported appar- 
ently exploited infrequent, large 
year classes (Jones et al., in press; 
Beckman et al. 1 ). The purpose of 
this study was to validate directly 
the ages of adult black drum by 
using mark-recapture methods. 
The sample of recaptured fish also 
provided insight into the popula- 
tion dynamics of black drum in 
east-central Florida. 
Materials and methods 
We used a 549-m nylon trammel 
net (124- and 356-mm mesh, inside 
and outside stretch, respectively) to 
capture adult black drum in the 
southern Mosquito Lagoon and 
northern Banana River areas of the 
Indian River Lagoon system along 
Florida’s Atlantic coast (Fig. 1). 
Black drum were captured for tag- 
ging in February, June, and Sep- 
tember 1992, and in February, 
June, and August 1993. Each fish 
was measured for total length 
(mm), tagged with a 100-mm Hall- 
print plastic dart tag, injected in- 
tramuscularly with approximately 
25 mg of oxytetracycline (OTC) per 
kilogram of body weight, and re- 
leased to the capture area. The dart 
tag was placed in the side of the fish 
about 25 mm ventral to the ante- 
rior insertion of the second dorsal 
fin. This placement allowed the 
barb to lodge behind a ptery- 
giophore while leaving the external 
message (streamer) visible. This 
external streamer bore an identifi- 
cation number and a message in- 
1 Beckman, D. W., C. A. Wilson, D. L. 
Nieland, and A. L. Stanley. 1990. Age 
structure, growth rates, and reproductive 
biology of black drum in the northern Gulf 
of Mexico. Final report, U.S. Dep. Com- 
merce Cooperative Agreement NA89WC- 
H-MF017, Marine Fisheries Initiative 
(MARFIN) Program, 77 p. 
Manuscript accepted 7 August 1997. 
Fishery Bulletin 96:382-387 (1998) 
