Fry: Sustenance of Farfantepenaeus aztecus in Louisiana coastal waters 
149 
Figure 1 
Study area along the Louisiana-Texas coast, northern Gulf of Mexico. River inflows important in this study are the Mis- 
sissippi River at the Bird’s Foot Delta, the Atchafalaya River along the central coast, and the Houston Ship Channel that 
flows into upper Galveston Bay. GB = Galveston Bay, TB=Terrebonne Bay, BB = Barataria Bay, BFD = Bird’s Foot Delta. 
The north-south dividing line between BB and BFD marks the zero-km reference used in Figure 3. SEAMAP=Southeast 
Area Monitoring and Assessment Program. 
Isotope studies are complementary to taxonomy-based 
studies of diets and generally show contributions from 
plants and bacteria in supporting food webs rather 
than details of predator-prey interactions (Fry, 2006). 
Taxonomic work was not part of this study but isotope 
data were collected for the proventriculus (stomach) 
contents of brown shrimp to help map river support of 
the benthic food web. The CNS isotope studies reported 
add to an extensive literature about shrimp isotopic 
variation in food webs of the Gulf of Mexico (Fry 1981, 
1983, 2008; Fry et ah, 1984, 2008) and also comple- 
ment recent studies of stable isotope studies of fish in 
the northwestern Gulf of Mexico (Roelke and Cifuentes, 
1997; Senn et al., 2010). 
Materials and methods 
Samples were collected from several locations in the 
northern Gulf of Mexico, from Galveston Bay in the 
west to the Bird’s Foot Delta in the east (Fig. 1). Most 
samples from Louisiana bays were collected during 
spring (April and May) brown shrimp trawl surveys 
conducted by LADWF in 1999 and 2005 in Barataria 
and Terrebonne bays. Additional shrimp were col- 
lected with seines during June 2006 in Terrebonne 
Bay and in the Bird’s Foot Delta. Offshore animals 
were collected during the National Marine Fisheries 
Service June- July summer SEAMAP (Southeast Area 
Monitoring and Assessment Program) surveys in 2005 
and 2006. Offshore station depths declined gradually 
from 10 m inshore near barrier islands to the 200-m 
isobath at about 28°N (Fig. 1) and included interme- 
diate mid-shelf areas regularly affected by summer 
hypoxia (Rabalais et ah, 2002). Offshore isobaths run 
approximately parallel to the coast through most of 
the study region. 
Shrimp were placed on ice and frozen soon after col- 
lection for 6-24 months until further processing. A few 
Galveston Bay samples were analyzed that were col- 
lected in previous studies in the 1990s and preserved 
in formalin (Rozas and Zimmerman, 2000). Preserva- 
tion in formalin has been shown to influence C and N 
isotope composition, but not S isotope values (Edwards 
et al., 2002). Accordingly, isotope values reported here 
for the Galveston Bay samples have been adjusted by 
