399 
Abstract— Experiments were conduct- 
ed to determine the effect of the salt-box 
catch-bycatch separation procedure, as 
used by the Texas shrimp industry, 
on short-term survival of bycatch. Bio- 
assays were conducted on five eco- 
nomically important bycatch species: 
spotted seatrout ( Cynoscion nebulo- 
sus ); red drum (Sciaenops ocellatus ); 
Atlantic croaker ( Micropogonias undu- 
latusY, southern flounder ( Paralichthyes 
lethostigma ); and blue crab iCallinectes 
sapidus). Red drum were most affected 
by hypersalinity, requiring 17 minutes 
exposure to a 70%c salt water solution 
to kill 50% of the test specimens within 
48 hours. For samples collected from 
commercial boats and Texas Parks and 
Wildlife (TPW ) trawl samples, we found 
that neither initial nor final percent 
survival was significantly different for 
bycatch removed with or without the 
aid of a salt-box. Bycatch mortality was 
high regardless of the method used 
to separate bycatch from the target 
catch. At the conclusion of catch sepa- 
ration, bycatch survival averaged 76% 
(±22%) for commercial samples and 
48% (±40%) for TPW trawl samples 
separated with salt-boxes. Survival at 
the conclusion of catch separation with- 
out a salt-box averaged 56% (±35%) for 
commercial samples and 43% (±39%) 
for TPW trawl samples. Bycatch sur- 
vival 21-27 h after catch separation 
averaged 13% (±6%-) for commercial 
samples and 5% (±9%) for TPW trawl 
samples separated with salt-boxes and 
34% (±29%) for commercial samples and 
10% (±19%) in TPW trawl samples sepa- 
rated without a salt-box. Mortality rates 
( M ) for bycatch separated with a salt- 
box averaged 0.08 (±0.03) for commer- 
cial samples and 0.10 (±0.04) for TPW 
trawl samples. For bycatch separated 
without the salt-box, M averaged 0.48 
(±1.23) for commercial samples and 0.10 
(±0.05) for TPW trawl samples. Results 
of an exploratory analysis with stepwise 
multiple regression suggested that final 
percent survival of bycatch was most 
affected by trawling time. The salt-box 
had little or no effect on bycatch sur- 
vival; therefore, regulating the use of 
salt-boxes in shrimp trawling operations 
is not necessary. 
Manuscript accepted 9 March 2001. 
Fish. Bull. 99:399-409 (2001). 
Effect of the salt-box catch-bycatch separation 
procedure, as used by the Texas shrimp industry, 
on short-term survival of bycatch 
Robert L. Colura 
Britt W. Bumguardner 
Perry R. Bass Marine Fisheries Research Station 
Texas Parks and Wildlife Department 
HC 02 Box 385 
Palacios, Texas 77465 
E-mail address (for R L. Colura): bob.colura@tpwd. state. tx. us 
Shrimp ( Penaeus spp. ) are the most 
important commercial seafood product 
in Texas, accounting for more than 
80% by weight and 93%- of the value 
of all Texas commercial fisheries land- 
ings (Robinson et al., 1996). Texas 
shrimp landings from 1986 through 
1995 were about 32,000-44,000 metric 
tons (t) annually. About 6400-8000 t 
of the annual catch during the 10-year 
period came from Texas bays. Texas bay 
shrimpers are reported to catch 2. 4-6. 8 
kg of nontarget species (bycatch) for 
each kg of shrimp landed (Fuls and 
McEachron, 1998). Removal of the 
bycatch is time consuming and thus 
costly to fishermen. To reduce the time 
spent removing bycatch, Texas bay 
shrimpers frequently use salt-boxes to 
assist in rapid separation of bycatch 
from shrimp (Bumguardner and Colura, 
1997). Salt-boxes are onboard tanks 
that hold a hypersaline solution of sea- 
water and food-grade salt. The catch 
is placed in the solution, where most 
fish species float and shrimp sink. 
Floating bycatch is skimmed from the 
surface and discarded. Shrimp are then 
dipped from the tank and any remain- 
ing bycatch removed and discarded. 
Although use of salt-boxes is known to 
fisheries managers, the effect of its use 
on the survival of discarded organisms 
is unknown. 
The objectives of our study were to 
assess the effects of the use of the salt- 
box on bycatch survival. This was ac- 
complished by first conducting bioas- 
says to determine the exposure time to 
hypersaline conditions that would af- 
fect survival of five economically impor- 
tant species known to occur as a part 
of the bycatch (Fuls and McEachron, 
1998). The combined effects of trawl- 
ing and exposure to hypersaline con- 
ditions in the salt-box were evaluated 
by comparing survival and mortality 
rates of bycatch (all species) and three 
major components of the bycatch (At- 
lantic croaker, Micropogonias undula- 
tus, sand seatrout, Cynoscion arena- 
rius, and spot, Leiostomus xanthurus ) 
separated with and without the aid of a 
salt-box. This comparison was made for 
a series of samples collected from Texas 
bay shrimp fishermen and a series of 
samples collected during control exper- 
iments conducted by Texas Parks and 
Wildlife (TPW) personnel using exper- 
imental trawls. The TPW control ex- 
periments were conducted to remove 
some of the variation caused by the 
differing fishing methods used by each 
bay shrimper (i.e. different lengths of 
time the trawl was fished). 
Materials and methods 
Bioassays 
Bioassays were conducted on spotted 
seatrout (Cynoscion nebulosus), red 
drum (Sciaenops ocellatus), Atlantic 
croaker, southern flounder (Pciralich- 
thys lethostigma), and blue crab (Cal- 
linectes sapidus). The species were 
selected because of their importance to 
Texas’ recreational or commercial fish- 
eries, or both (Weixelman et al., 1992; 
Robinson et al., 1996) and because they 
are known to occur as a portion of the 
bycatch (Fuls and McEachron, 1998). 
Red drums and blue crabs were col- 
