600 



Fishery Bulletin 102(4) 



growth of a random population. Tournament anglers 

 target large fish, possibly the fastest growing individu- 

 als at a given age, and their catches may bias growth 

 estimates (Ottera, 1992; Vaughan and Burton, 1993; 

 Goodyear, 1995). Without these tournament fish, how- 

 ever, the Alabama red snapper TW model did not reach 

 an asymptote. Therefore the growth parameters for 

 that model were poorly estimated. Notwithstanding, 

 Alabama and Louisiana models did not differ signifi- 

 cantly. Estimates of W m and k predicted for Louisiana 

 red snapper were slightly larger than previously re- 

 ported for fish from the Louisiana commercial and 

 recreational catches (Render, 1995). Although the Texas 

 model predicted a value of W c . that was significantly 

 less than those for both Alabama and Louisiana red 

 snapper, Texas had a growth coefficient (k) that was 

 larger then that for Alabama. It appears that, as in the 

 length models, Texas fish reach a smaller theoretical 

 maximum weight but at a faster rate than Alabama 

 fish. Louisiana fish attained maximum weight at a 

 faster rate than Alabama or Texas red snapper. Our 

 growth models indicate that although Texas red snap- 



10 



B 



01 23456789 10 



Age (yr) 



Figure 6 



Scattergram with linear regression lines for relationships 

 (A) between age (yr) and mean fork length (mm) and (B) age 

 (yr) and mean total weight (kg) for red snapper (Lutjanus 

 campechanus) aged 1 to 10 years from the 1999-2001 rec- 

 reational harvests of Alabama. Louisiana, and Texas. Krror 

 bars represent standard deviations from the mean. 



per grow in mass at a faster rate than Alabama fish. 

 Texas red snapper are consistently smaller at age and 

 reach smaller maximum sizes than those from Alabama 

 and Louisiana and that there is a veritable difference 

 in size at age and growth rates among regions. Similar 

 demographic variations in growth rates among popula- 

 tions have been previously noted for other marine fish 

 species of the South Atlantic and GOM, such as gray 

 snapper (Johnson et al., 1994; Burton 2001), and king 

 mackerel (DeVries et al, 1990; DeVries and Grimes, 

 1997). 



Linear regressions of mean FL and mean TW at age 

 for red snapper aged one to 10 years indicated that only 

 TW was significantly different among sample regions. 

 Texas red snapper were shown to differ significantly 

 from both Alabama and Louisiana red snapper in re- 

 gressions of mean weight at age. Although comparisons 

 of FL at age for all regions were not significantly differ- 

 ent, Texas fish were significantly smaller in mass (TW) 

 at age than fish from Alabama and Louisiana. This 

 difference was observed in all age classes. 



Our research efforts indicate that there is mounting 

 evidence for discrete differences in size at age 

 and in overall growth rates between red snapper 

 sampled from the north central GOM (Louisiana 

 and Alabama) and the southwest GOM (Texas). 

 Texas red snapper are clearly reaching smaller 

 maximum sizes and are consistently smaller (TWi 

 at age than those collected from Louisiana and 

 Alabama waters. Although the reasons behind 

 these differences remain uncertain, logic indicates 

 that factors such food availability, habitat prefer- 

 ence, and actual population size may cause these 

 differences between regions. 



The more productive, nutrient-rich waters of 

 the Mississippi River and north-central GOM off 

 Louisiana and Alabama may be more conducive 

 to faster growth than the less fertile waters off 

 Texas. Approximately 70-80% of GOM fishery 

 landings come from the waters surrounding the 

 Mississippi River delta (Grimes, 2001). The west- 

 ern GOM (including the sampling area of Port 

 Aransas, TX) is devoid of a contributing river sys- 

 tem anything remotely similar to the Mississippi 

 River. Draining 43% of the continental United 

 States, the Mississippi River is the largest river 

 system in North America and provides an enor- 

 mous amount of nutrient-laden fresh water to the 

 shallow continental shelf of the northern GOM. 

 Although the mechanics by which the Mississippi 

 River enhances fishery production remain uncer- 

 tain. Grimes (2001) postulated that the discharge 

 from the Mississippi primarily influences recruit- 

 ment m the plume field. Increased growth rates 

 associated with the Mississippi River plume com- 

 pared with other regions of the GOM have been 

 noted for a number of species, such as gulf menha- 

 den (Warlen, 1988), king mackerel (DeVries et al., 

 1990), striped anchovy (Day, 1993), and yellowfin 

 tuna (Lang et al., 1994). 



