400 
Fishery Bulletin 99(3) 
Table 1 
Exposure times, salinity, temperature, and number of individuals per replicate used in high-salinity exposure bioassays. Three 
replicates were used at each exposure time. 
Species 
Exposure times 
(min) 
Salinity 
(' %o ) 
Temperature 
(°C) 
Bay water salinity 
(%o) 
Fish/ 
replicate 
Red drum 
4, 8, 16, 32, 64, 128 
70 
24 
19 
10 
Atlantic croaker 
4,8, 16,32,64, 128 
70 
23 
16 
5 
Spotted seatrout 
4, 8, 16, 32, 64 ; 
69 
26 
24 
5 
Southern flounder 
4, 8, 16, 32, 64, 128 
71 
27 
18 
5 
Blue crab 
4,8, 16,32,64, 128 
70 
26 
24 
5 
' Specimens did not survive to 128 min of exposure. 
lected from TPW hatchery ponds; Atlantic croaker and 
southern flounder were collected from Matagorda Bay 
with a trawl; spotted seatrout were collected form East 
Matagorda Bay with a bag seine. Fish were held 7-10 
days in 1850-L tanks at ambient bay salinities and tem- 
peratures and fed frozen brine shrimp or chopped shrimp 
(or both) three times daily. Blue crabs were placed in hold- 
ing tanks for one day prior to bioassay initiation. Juve- 
nile blue crabs molt at frequent intervals and because of 
their aggressive nature, any soft crabs in a common tank 
are almost immediately cannibalized. Therefore, blue crab 
trials were held before substantial mortality occurred in 
holding tanks and without an initial acclimation period. 
Bioassay trials were conducted at salinities of 70%c 
(±1 %c) and temperatures from 23 to 27°C. A salinity of 70%<? 
was selected on the basis of salinities observed in salt- 
boxes on commercial shrimping vessels (Bumguardner and 
Colura, 1997). Trials were conducted over a geometric se- 
quence of times up to 128 minutes with three replicates 
for each time (Table 1). Either 5 or 10 individuals were 
exposed for each replicate, depending on size and avail- 
ability. Test animals were placed in 4-L all-glass aquaria 
that had been washed with acid and alcohol and filled with 
about 3-L of 70 %c salt water. Air was continuously bubbled 
through the water from a 1-mL disposable pipette attached 
to an air blower. High-salinity water was obtained by add- 
ing salt (Mortons Ship n Shore®) purchased from a fishing 
supply store to water taken from Matagorda Bay. Salinity 
levels of bay water for each trial are presented in Table 
1. Animals were removed from test aquaria at the end of 
the specified exposure time, high-salinity water was dis- 
carded, the aquarium was refilled with bay water, and ani- 
mals were replaced in the aquaria. So that control animals 
were treated similarly, they were placed in the aquaria 
containing bay water and held for 60 minutes, after which 
these animals were removed, the bay water replaced with 
new bay water, and the control animals returned to the 
aquaria. The number of live individuals was recorded for 
each replicate immediately after high-salinity exposure, 
24 hours after exposure, and 48 hours after exposure. For 
each species, probit analysis was conducted on untrans- 
formed data to determine the time at which 50% of the test 
animals exposed to the test salinity died (LE 50 ) (Sokal and 
Rohlf, 1981). A no-observed-effect exposure (NOEE) (Rand 
and Petrocelli, 1985) for each species was calculated by us- 
ing a multiple goodness-of-fit comparison of log-likelihood 
ratio G values (Sokal and Rohlf, 1981). 
Effect of salt-box use on bycatch survival: samples 
from the bay shrimp industry 
Thirty samples of bycatch were collected from May through 
October 1995 from bay shrimpers working in Matagorda, 
San Antonio, and Aransas bays. Fifteen samples were sep- 
arated with a salt-box (SB) and the remaining 15 samples 
were separated without the aid of a salt-box (NSB). For 
each sample the following data were collected: 
1 Length of time that trawl was fished; 
2 Time that catch was removed from water; 
3 Time that separation procedure began; 
4 Time that bycatch was returned to water; 
5 Bay temperature; 
6 Bay salinity; and 
7 Salinity in salt-box. 
Total catch weight was not measured because bay shrimp- 
ers do not weigh individual catches and we did not want 
to change their shrimping practices more than necessary 
to collect the samples. To collect bycatch samples, an indi- 
vidual boarded the boat and waited until the bycatch was 
discarded. A 1-2 kg sample was randomly removed from 
the bycatch with a dip net or plastic scoop and placed into 
a 60-cm diameter x 60-cm deep holding pen. Pens were 
constructed from a bag of 15-mm stretch-mesh knotless 
nylon net secured to a life ring. The opening in the life 
ring served as the opening of the pen. After the sample 
was placed in the pen, the opening was covered with 6-mm 
stretch-mesh netting. The pen was then placed overboard 
where TPW personnel in another boat recovered it. The 
samples, when brought aboard the TPW boat, were imme- 
diately placed in separate 89-L transport tanks (ice chests 
fitted with plastic tubing and commercial aquarium air 
stones, through which compressed oxygen was supplied 
to the tanks). Dead organisms were removed from sam- 
ples immediately after placement in the transport tanks. 
