622 
Fishery Bulletin 99(4) 
Figure 6 
Scatterplot of red snapper TL-at-age data for all fish assigned ages. Plotted 
line is the von Bertalanffy growth function fitted to the data. 
Weight = (4.68 x 10 ~ 9 )7X 317 
(F V1 467 =85,961; PcO.OOl; r 2 =0.98). 
Mark-Recapture 
A total of 2932 adult red snapper were tagged. Total length 
at recapture was measured for 288 of 519 recaptured 
individuals. Mean TL (±SE) of recaptures was 344 (±4.1) 
mm (range: 183-660 mm) at release and 423 (±5.6) mm 
(range: 253-726 mm) at recapture, and mean time at lib- 
erty (±SE) was 334 (±16.3) d (range: 12-1501 d). Predicted 
TL from Faben’s method corresponded well to observed TL 
at recapture for tagged fish (Fig. 8). The linear regression 
of change in TL on days at liberty was statistically sig- 
nificant (F 1286 =631.0, P<0.001, r 2 =0.76) and had a slope 
of 0.238 mm/d (Fig. 9A). The range in estimated ages of 
otolith-aged fish for the linear regression of TL on age 
was 356-2599 d (approximately one to seven years). The 
model was statistically significant (F 11 541 =6309, PcO.OOl, 
r 2 =0.80) and had a slope of 0.240 mm/d (Fig. 9B). 
Discussion 
Validating the periodicity of opaque zone formation in oto- 
liths as annual is imperative for age and growth studies 
where otoliths are used as aging structures (Beamish and 
McFarlane, 1983, 1987). Annual formation of opaque zones 
in otoliths has been validated for several tropical and su- 
tropical lutjanids (Manooch, 1987; Fowler, 1995; Cappo et 
al., 2000), and annual formation of opaque zones in red snap- 
per sagittae has been reported from the northwestern GOM 
and the southeastern U.S. Atlantic (Render, 1995; Manooch 
and Potts, 1997; Wilson and Nieland, 2001). Our marginal 
increment analysis of red snapper otoliths demonstrates 
that opaque zones in adult red snapper sagittae also are 
formed annually in the north central GOM. The pattern of 
monthly marginal increment scores reveals that some fish 
begin opaque zone formation as early as November and some 
do not have translucent margins until midsummer; however, 
the general pattern of opaque zone formation is from Jan- 
uary through May. Render (1995) and Wilson and Nieland 
(2001) have reported a similar pattern for adult red snapper 
in the northwestern GOM, and opaque zone formation in 
winter-spring has been shown for sagittae of several other 
teleosts in the northern GOM (Maceina et al., 1987; Beck- 
man et al., 1989, 1990, 1991; Thompson et al., 1999). 
Because relatively few old red snapper were sampled in 
our study, and samples of old fish came mostly from tour- 
naments in summer months, we were unable to validate 
ages beyond 8 years. Baker ( 1999) compared age estimates 
of otolith-aged GOM red snapper with age estimates from 
radiometric dating of their otolith cores and reported that 
age estimates from the two methods were highly correlat- 
ed for fish up to 37 yr old, thus corroborating otolith-based 
estimates of age for older fish. Therefore, despite lack of 
annulus validation for older red snapper ages in our study, 
we are confident that otolith-based age estimates of older 
individuals are accurate. 
Age and growth 
Red snapper are long-lived reef fish; we observed a maxi- 
mum age of 34 yr for females and 33 yr for males. Other 
