82 
Fishery Bulletin 1 15(1) 
Table 2 
Mean densities, measured in individuals per square meter, of juvenile white shrimp {Litopenaeus setiferus) in Sabine Lake 
during 6 sampling trips in 2011 in 3 salinity zones (intermediate, brackish, and saline) and 4 habitat types: 1 — marsh edge, 
or marsh vegetation <1 m from the interface of marsh and open water (ME); 2 — shallow water <1 m from the marsh edge 
(SWl); 3 — shallow water 1-5 m from the marsh edge (SWl-5); and 4 — shallow water >5 m from the marsh edge (SW>5). A 
dash indicates that no sample was taken in that habitat on that date. Sample sizes for each mean range from 5 to 10 and 
are provided in Table 1. Standard errors (SEs) of the means are given in parentheses. 
Zone 
Intermediate Brackish Saline 
Trip 
ME 
SWl 
SWl-5 
SW>5 
ME 
SWl 
SWl-5 
SW>5 
ME 
SWl 
SWl-5 
SW>5 
1 
_ 
1.2 (0.8) 
0.0 (0.0) 
0.0 (0.0) 
_ 
11.2 (5.9) 
0.4 (0.4) 
2.4 (1.9) 
_ 
6.0 (5.3) 
7.6 (4.4) 
1.6 (0.7) 
2 
- 
7.8 (4.7) 
0.4 (0.4) 
0.0 (0.0) 
- 
13.6(2.7) 
4.6 (4.1) 
3.0 (2.0) 
63.0 (28.2) 
29.4 (26.2) 
3.8 (3.1) 
4.0 (1.5) 
3 
- 
12.0 (5.3) 
1.4 (0.5) 
0.0 (0.0) 
- 
27.7(10.4) 
1.0 (0.8) 
2.2 (1.6) 
- 
46.4(11.7) 
29.4(12.2) 
10.0(3.2) 
4 
61.8(25.4) 
25.2 (9.4) 
0.4 (0.4) 
0.2 (0.2) 
74 (22.1) 
58.6(23.1) 
2.8 (1.5) 
1.8 (0.6) 
60.4 (24.4) 
65.0 (36.2) 
6.2 (3.9) 
10.4 (3.4) 
5 
16.0(4.7) 
19.4 (4.8) 
0.4 (0.4) 
0.6 (0.6) 
64.8 (20.0) 
51.0(15.8) 
8.4 (5.1) 
1.6 (0.9) 
43.0(9.2) 
9.0 (3.9) 
10.8 (3.7) 
5.6 (2.6) 
6 
46.8(12.6) 
47.8 (20.7) 
4.0 (1.3) 
0.6 (0.2) 
31.4(13.4) 
28.8 (6.6) 
5.8 (2.1) 
9.4 (8.4) 
174.0 (74.6) 
33.0(16.1) 
17.0 (3.8) 
22.8 (3.5) 
Overall mean 
41.5(10.2) 
17.9 (4.2) 
11(0.3) 
0.2 (0.1) 
56.7(11.2) 
31.2 (5.5) 
3.8 (1.2) 
3.4 (1.5) 
85.1(22.6) 
33.6 (7.8) 
12.4 (2.8) 
9.1 (1.6) 
Table 3 
Results of 3-way analysis of variance (ANOVA) to examine differences in mean density of ju- 
venile white shrimp (Litopenaeus setiferus) among salinity zones, habitat types, and sampling 
trips in Sabine Lake in 2011. A measure of effect size, omega squared (co^), is given for each 
factor and can be interpreted as an estimate of the proportion of variance accounted for by each 
source of variation. Data used in this analysis were obtained from trips 4-6. 
Factor 
df 
Sum of squares 
F ratio 
P 
0)^ 
Zone 
2 
27.90 
13.86 
<0.0001 
0.06 
Trip 
2 
8.80 
4.37 
0.0143 
0.02 
Habitat type 
3 
208.57 
69.10 
<0.0001 
0.45 
Zone*Trip 
4 
13.35 
3.32 
0.0124 
0.02 
Zone*Habitat type 
6 
25.30 
4.19 
0.0006 
0.04 
Trip*Habitat type 
6 
8.92 
1.48 
0.1899 
0.01 
Zone*Trip*Habitat type 
12 
13.70 
1.34 
0.3373 
0.00 
Error 
144 
144.90 
p 
ii 
Discussion 
The suitability of habitat for juvenile white shrimp 
varies among salinity zones within Sabine Lake. The 
saline and brackish zones provide more important 
nursery habitat for white shrimp than does the inter- 
mediate zone, on the basis of our estimates of shrimp 
density, growth, and secondary production. The inter- 
mediate zone contains the least important nursery 
area, although shrimp mortality rates were lower there 
than in the 2 other salinity zones. Although growth, 
mortality, and secondary production, together with den- 
sity, are considered necessary for a comprehensive as- 
sessment of nursery habitat (Beck et ah, 2001), and 
density alone may sometimes be a misleading indica- 
tor of habitat quality (Van Horne, 1983), in our study. 
density appeared to be an accurate indicator of habitat 
quality for juvenile white shrimp. 
Habitat type accounted for most of the variation in 
density of white shrimp. Density of white shrimp was 
highest for habitat <1 m from the marsh edge and de- 
clined with increasing distance into open water in all 
3 salinity zones. This general pattern for white shrimp, 
namely high density near the marsh edge and a decline 
in density in open water, has been observed in another 
area of Sabine Lake (Nevins et al., 2014), in Galveston 
Bay, Texas (Minello et al., 2008), and in Barataria Bay, 
Louisiana (Rozas and Minello, 2015). Densities of white 
shrimp at the marsh edge sites in our study area were 
among the highest densities reported for this species 
in the northern Gulf of Mexico. This concentration of 
shrimp may be a response to the short flooding dura- 
