Saari et al.: Regional differences in the age and growth of Lut/anus campechanus in the Gulf of Mexico 
267 
Age (y) 
Figure 3 
Frequency distributions of age (in years) for red snap- 
per ( Lutjanus campechanus ) sampled in 2009 and 
2010 from 6 recreational fishing regions in the Gulf 
of Mexico: (A) South Texas ( /r =348 ) and North Texas 
(n=224), (B) Louisiana (n=268) and Alabama (n=204), 
and (C) Northwest Florida (n=463) and Central Florida 
(n=301). 
snapper across the GOM. Sample sizes were fairly con- 
sistent among the regions, allowing us to compare the 
trends in size at age and growth over the age ranges 
collected. The consistently smaller size at age, small 
estimates for maximum TL, and high k estimates for 
fish from South Texas and Northwest Florida are in- 
dicative of the highly truncated age structure and over- 
exploitation in each region (Trippel, 1995; Rose et al., 
2001; Berkeley et al., 2004; Nieland et al., 2007) and 
may be attributable also to variations in fishing regime 
(Fischer et al., 2004). 
Although differences were found among the regional 
von Bertalanffy growth models, very few old fish were 
observed. As a result, the models were extrapolated 
beyond the range of data and may not be fully repre- 
sentative of each subpopulation. The absence of larger, 
older fish may strongly prevent the models from reach- 
ing an accurate asymptote (maximum size) (Haddon, 
2001) . Also, very few fish under the age of 3 years were 
included in our samples because of the minimum size 
limit on the recreational fishery (>406.4 mm maximum 
TL). Therefore, the models were forced through £q= 0 
to more accurately predict juvenile growth, a selection 
that may increase k estimates. Nonetheless, the k es- 
timates from this study were comparable to estimates 
from previous studies (Patterson et al., 2001b; Wilson 
and Nieland, 2001; Fischer et al., 2004). 
In contrast to red snapper in South Texas, the slow- 
er-growing red snapper from North Texas appear to be 
more similar to fish in Louisiana and Alabama. These 
findings are consistent with reports of significant post- 
settlement movement of juveniles (0-2 years) between 
the northern and western GOM, as well as with otolith 
microchemistry analysis and larval transport studies 
that indicate that recruitment in the western GOM is 
subsidized by recruits from Louisiana (Patterson, 2007; 
Patterson et al., 2008; Johnson et al., 2009; Sluis, 2011). 
These observed differences may also be attributable 
to mixing of stocks between South Texas and Mexico 
because the Mexican stock is severely overfished and 
dominated by small, fast-growing fish (Garcia et al., 
2002) . To date, no direct comparisons of red snapper 
age and growth from Mexican and U.S. waters have 
been made. However, in a recent otolith microchemistry 
study the source of recruits to the Texas continental 
shelf was determined to be derived from a combination 
of the Texas, Louisiana, and Mexico substocks (Sluis, 
2011). Sluis (2011) also found a large contribution of 
the Louisiana substock to the eastern GOM. Therefore, 
the similarities observed in this study for red snapper 
between the Louisiana and Central Florida regions may 
be indicative of regional connectivity through offshore 
currents that flow clockwise along the outer continen- 
tal shelf and potentially transport larvae and adults 
(Ohlmann and Niiler, 2005; Johnson et al., 2009). 
The potential mechanisms for the observed demo- 
graphic variation include environmental factors, fish- 
ing pressure (including localized population respons- 
es), habitat preference, and management regimes in 
the different regions (e.g., state regulations). Numer- 
ous environmental differences, including availability 
of suitable habitat, productivity of the surrounding 
ecosystem, and community structure could have con- 
tributed to the demographic dissimilarity among the 
regions. The productive, nutrient-rich waters of the 
Mississippi River plume have been shown to influence 
