80 
Fishery Bulletin 115(1) 
Figure 3 
Comparison of mean flooding duration (number of hours 
water depth was > 5 cm/total number of hoursxlOO) for 
marsh edge and shallow-water sites among 3 differ- 
ent salinity zones (intermediate, brackish, and saline) 
in Sabine Lake from July 2011 through October 2011. 
Negative values indicate distances (from the marsh 
edge) within marsh vegetation, and positive values 
are distances from the marsh edge over shallow water. 
Means and standard errors (1 SE) were calculated from 
20 replicate measurements. 
siana experienced drought conditions starting in late 
2010 until the end of 2011 (NOAA National Centers for 
Environmental Information, Climate Data Online, web- 
site, accessed October 2015). As a result, mean salini- 
ties during our study in Sabine Lake were slightly out- 
side the range typical for the brackish zone and well 
above the normal range for the intermediate zone (Fig. 
2). Mean water temperature varied little among salin- 
ity zones during each sampling trip and was slightly 
lower during the last 3 trips than during the first 3 
trips. Mean dissolved oxygen was less variable during 
the first 3 sampling trips than during the last 3 trips, 
but no clear trend was detected in dissolved oxygen 
among salinity zones. We observed no consistent trend 
in either mean water depth or turbidity among salin- 
ity zones. 
Flooding duration varied among salinity zones and 
distances from the marsh edge (Fig. 3). The marsh edge 
habitat was flooded for the highest percentage of the 
time in the intermediate zone (70%), followed by the 
brackish (50%) and saline (42%) zones. The mean dura- 
tion of flooding of the vegetated marsh surface >0.5 m 
from the marsh edge (i.e., the negative numbers on the 
a:-axis in Fig. 3) was relatively short (<20% of the time) 
in all 3 salinity zones. In the saline zone, shallow-water 
sites within 5 m of the marsh edge were flooded for 
relatively short durations as well (Fig. 3). 
Size 
White shrimp ranged in size from 4 to 126 mm TL, 
on the basis of data from all 6 sampling trips to the 
3 salinity zones. Most shrimp (98%), however, were ju- 
veniles <60 mm TL, and, in general, size distributions 
and mean sizes were similar among salinity zones and 
sampling dates (Fig. 4). Mean size on most sampling 
dates ranged from 12 to 35 mm TL, except in the in- 
termediate zone on trip 5 when mean size was 41 mm 
TL. 
Density 
Mean densities varied among habitat types, salinity 
zones, and sample dates (Table 2). The overall ANO- 
VA model was significant (P<0.001) and accounted for 
60% of the variation in the shrimp density data. All 3 
main effects were significant, as were the interactions 
between habitat type and salinity zone and between 
salinity zone and sampling trip; the 3-way interaction 
was not significant (Table 3). 
Habitat type was the most important factor in the 
model, and it accounted for an order of magnitude 
more variation (45%) in the density data than that of 
any other factor (<6%, Table 3). The interaction of habi- 
tat type with salinity zone was weak, accounting for 
only 4% of the variation in the density data. Results 
from a priori contrasts indicated that shrimp densities 
were higher in the marsh edge habitat than in adja- 
cent shallow water (P=0.0379), higher in shallow water 
near the marsh edge than in other shallow-water sites 
(P<0.0001), and higher at the marsh edge sites than at 
all shallow-water sites combined (P<0.0001). 
Mean shrimp density in each habitat type was gen- 
erally highest in the saline zone. For example, mean 
shrimp densities at the marsh edge sites were estimat- 
ed as 41.5 individuals/m^ (standard error [SE] 10.2), 
56.7 individuals/m^ (SE 11.2), and 85.1 individuals/ 
m^ (SE 22.6) for the intermediate, brackish, and sa- 
line zones, respectively (Table 2). The SWl habitat type 
was an exception; mean density at this type of habitat 
(based on the last 3 sampling trips) was highest in the 
brackish zone and lowest in the intermediate zone (Fig. 
5). Although the main effect of salinity zone was signif- 
icant, this effect varied by sample date; mean density 
was usually highest in the saline zone, except for on 
trip 5 when mean density was higher in the brackish 
zone than in the saline zone (Fig. 6). 
Mortality 
We estimated mortality by combining shrimp length- 
frequency data from the last 3 sampling trips in each 
salinity zone and conducting 2 catch-curve analyses 
per zone. Within a salinity zone, no difference in mor- 
tality rates could be detected between the results of 
the 2 catch-curve analyses (Table 4). Among salinity 
zones, no statistically significant difference in mortal- 
ity rates was detected between the saline (0.09 [SE 
