Stoner: Discard mortality for Alaskan crabs after exposure to freezing temperatures 
459 
Table 6 
Results of logistic modeling for mortality in Chionoece- 
tes opilio (snow crab). A backward stepwise approach was 
used to determine the most parsimonious model for mor- 
tality, with an alpha value of 0.15 to remove a variable 
from the full model. 
Parameter 
Estimate Z 
P value 
Full model 
constant 
-4.135 
-1.323 
0.186 
temperature 
0.644 
1.088 
0.277 
crab size 
0.015 
0.426 
0.670 
reflex impairment 
0.926 
5.298 
<0.001 
Most parsimonious model 
constant 
-1.868 
-3.972 
<0.001 
reflex impairment 
0.864 
5.288 
<0.001 
Prediction matrix for the most parsimonious model 
Dead 
Live 
Actual 
predicted 
predicted 
total 
Die 
50 
12 
62 
Live 
9 
31 
40 
Total no. predicted 
59 
43 
102 
Correct (%) 
84.7 
72.1 
False (%) 
15.3 
27.9 
Total correct (%) 
79.4 
When reflexes were reassessed at the end of the 9-day 
holding period average impairments had decreased (i.e., 
condition improved) since the first assessment. This was 
true for both crab species and for both -20° and -10°C 
temperature treatments. However, most of the crabs 
with high initial reflex impairments died. More impor- 
tantly, most individuals demonstrated either no change 
in reflex actions (85.1% of C. bairdi; 94.9% of C. opilio) 
or improvement during the holding period, and only a 
few individuals showed a one point increase in impair- 
ment. None of the control crabs died in holding and all 
had perfect reflex scores at the end of the experiment. 
Discussion 
Cold exposure and mortality 
Although numerous studies have explored the effects 
of air exposure on economically significant crustaceans 
(e.g., Brown and Caputi, 1983; Vermeer, 1987; DiNardo 
et al., 2002; Lorenzon et al., 2007), and fishes (Olla et 
al., 1998; Davis et al., 2001; Gingerich et al., 2007) few 
experiments have been conducted to evaluate the effects 
of freezing temperatures relevant to high-latitude fish- 
eries. In the present study, exposure to cold air caused 
high levels of mortality in C. bairdi and C. opilio , and 
the relationships to degree-hours of exposure were simi- 
Reflex impairment 
Figure 6 
Relationships between percent mortality of Chionoecetes 
bairdi (Tanner crab) and C. opilio (snow crab) and reflex 
impairment. Results are shown for exposure treatments 
made at two different temperatures where at least four 
crabs represent a point (open symbols) (see Fig. 5) and for 
pooled data (closed circles). The fitted curves represent 
results of logistic regression, and show the probabilities 
of mortality for the two crab species with varied levels 
of reflex impairment. 
lar to those observed by Carls and O’Clair (1995) for C. 
bairdi. They reported a median lethal exposure for C. 
bairdi equal to -3.3°h for juveniles (46-74 mm CW) and 
-4.3°h for adult females (85-124 mm CW). The latter 
value corresponds closely with a median of approxi- 
mately -4.8°h for male C. bairdi and -4.3°h for male C. 
opilio. Although the degree-hour exposure metric used 
in this and earlier studies provides a good integration 
of temperature and time, it is also clear that variation 
in mortality occurs with animal size (Carls and O’Clair, 
1995), wind chill effect (Warrenchuk and Shirley, 2002), 
test temperature (this study), and other environmental 
variables (van Tamelen, 2005). Furthermore, large dif- 
ferences in mortality rates for C. opilio between this 
study and that conducted by Warrenchuk and Shirley 
(2002) illustrate the importance of specific environ- 
mental conditions. For example, in their study only 
five minutes exposure to windchill of -16°C (— 1.33°h) 
resulted in 100% mortality. In comparison, the closest 
