Mace and Rozas: Population dynamics of juvenile Litopenaeus setiferus 
79 
Figure 2 
Mean water (A) salinity, (B) temperature, (C) dissolved oxygen, (D) turbidity (in 
nephelometric turbidity units, NTUs), and (E) depth within intermediate, brack- 
ish, and saline zones measured on 6 trips during which samples of juvenile white 
shrimp (Litopenaeus setiferus) were collected in 2011. Means and standard errors 
(1 SE) were computed from 15 to 20 replicate measurements. 
fore, growth rates could have affected our age esti- 
mates and the resultant CPI. We used a conservative 
approach for initial estimates of secondary production 
by assuming that shrimp in each salinity zone had the 
same CPI of 53 d (i.e., the maximum age of a shrimp 
since recruitment to the population as a 7 mm TL post- 
larva until migration out of the population at 60 mm 
TL, assuming a growth rate of 1 mm TL/d). We also 
calculated secondary production using CPIs for shrimp 
in each salinity zone based on the growth rates we es- 
1 timated as described above. For example, if the mean 
growth rate that we estimated for a salinity zone was 
2 mm TL/d, a 60-mm-TL shrimp that arrived in the 
population at 7 mm TL would have aged 27 d since it 
arrived in the population. Therefore, the CPI based on 
this 2 mm TL/d growth rate would be 27. 
Results 
Environmental variables 
Environmental variables, other than salinity, differed 
little among salinity zones (Fig. 2). Southwest Loui- 
