406 
Fishery Bulletin 99(3) 
Table 9 
Species collected from samples of bycatch separated with or without the aid of a salt-box in control experiments whose mean total 
length (mm) differed significantly and results of Wilcoxon signed rank tests used to compare the means. 
Species 
Salt-box 
No salt-box 
Z 
P 
Mean total length ±SD 
n 
Mean total length ±SD 
n 
Bay anchovy 
50 ±11 
191 
53 ±13 
219 
-2.977 
<0.001 
Spot 
94 ±18 
138 
89 ±24 
194 
2.818 
0.005 
Silver perch 
72 ±37 
4 
111 ±22 
18 
-2.605 
0.009 
Atlantic brief squid 
82 ±39 
53 
58 ±39 
63 
4.177 
<0.001 
bay temperature explained 85% of the variation associated 
with estimates of bycatch M. Catch separation time was the 
most important of the three, explaining 79% of the varia- 
tion. Catch separation time explained 52% of the variation 
observed in initial survival and was the only variable to 
meet the P< 0.05 significance level required for entry into 
the model. Trawling time explained 48% of the variation ob- 
served in bycatch final survival and use or non-use of a salt- 
box explained the remaining 11%. For the dependent vari- 
able, Atlantic croaker final survival, the use or non-use of 
a salt-box explained 38% of the variation explained by the 
model and catch separation time explained an additional 
11%. The five independent variables did not meet the P<0.05 
significance level required to enter or stay in stepwise re- 
gression models for Atlantic croaker initial survival and M. 
Effect of salt-box use on bycatch survival: control 
experiments 
Twenty-eight species were collected for the control experi- 
ments: 24 fishes and 4 invertebrates (Table 4 ). Bay anchovy 
(n=3794), Atlantic croaker (n=2048), spot (n=949), sand 
seatrout (n=291), and Gulf menhaden (n=148) were the 
most numerous organisms and were observed in more 
than half the samples collected. Remaining fishes aver- 
aged <1 individual per sample. Brown shrimp (n=494) and 
Atlantic brief squid ( Lolliguncula brevis, n = 133) were the 
most numerous invertebrates caught. By species, no sig- 
nificant differences were found between numbers of indi- 
viduals in SB and NSB samples. Bay anchovy, spot, silver 
perch ( Bairdiella chrysoura), and Atlantic brief squid col- 
lected in NSB samples were significantly larger than those 
collected in SB samples, but differences for the most part 
were small or the organism was present in small numbers 
(Table 9). Remaining species were similar in size in both 
NSB and SB samples. Catch separation time averaged 12 
min (±6 min) for SB samples and 18 min (±18 min) for 
NSB samples and was significantly different (Z=2. 05399, 
P=0.04). At the time samples were collected, bay tempera- 
ture averaged 26.0° (±3.1°)C, bay salinity, 18,0%t>. (±7.2%e), 
and salt-box salinity 66%e (±8%o). 
Survival rates and mortality rates were highly variable 
for bycatch separated by both methods. Mean initial sur- 
vival rates were 48.4% (±39.7%) and 43.6% (±39.3%), re- 
spectively for SB and NSB samples. Final survival rates 
were 5.4% (±8.9%) for SB samples and 9.5% (±18.7%) for 
NSB samples. Mortality rates averaged 0.1 (±0.04) for SB 
samples and 0.1 (±0.05) NSB samples. All estimates of 
survival and mortality were statistically similar (Table 
10). By species, estimates of initial survival, final survival, 
and M for Atlantic croaker, spot, and sand seatrout were 
also highly variable and were statistically similar between 
the two methods of bycatch separation. 
Spearman correlation coefficients significantly greater 
than 0 demonstrated a relationship between bycatch (all 
species) catch separation time and the variables initial 
survival (r s =0.445) and M(r s =0.522). (Table 11). Initial sur- 
vival was found to have an inverse relationship with tem- 
perature. All three measurements of the effect of salt-box 
use on bycatch were associated with the frequency of oc- 
currence of some species in the bycatch. The variable M 
was positively correlated to Atlantic croaker (r s =0.765), 
spot (r s =0.681), and sand seatrout (r s =0.792) numbers. Ini- 
tial survival was positively correlated to Atlantic croaker 
(;’ s =0.630), spot(?' s =0.530), and blue crab (r s =0.494) num- 
bers and was inversely related to the numbers of bay an- 
chovy (r s =- 0.795) and Gulf menhaden (r s =-0.466). Final 
survival was positively correlated to blue crab (r s =0.631) 
numbers and inversely related to bay anchovy numbers 
(r s =-0.655). Other species to which M, and initial and fi- 
nal survival were related occurred in fewer than half the 
samples and averaged <1 organism per sample. Atlantic 
croaker M was related to bay temperature (r s =0.828), bay 
salinity (r s =-0.513), and to the presence of Atlantic brief 
squid (r s =-0.833). Neither Atlantic croaker initial nor final 
survival estimates were correlated to other variables. Spot 
and sand seatrout M, initial survival, and final survival 
were not correlated to any variable. 
For all species, stepwise multiple regression identified 
catch separation time, bay salinity, and bay temperature at 
the time of sample collection as significant variables which 
explained some of the observed variation in M and final 
survival (Table 12). The salt-box variable did not enter any 
model. Catch separation time explained 27% of the varia- 
tion that was accounted for by the model for the dependent 
variable M, and an additional 11% was explained by bay 
salinity at time of sample collection. Bay temperature and 
salinity at the time of collection explained 34% of variation 
observed in the final survival model. No variable met the 
P<0.05 significance level for entry into regression models 
