Stoner: Discard mortality for Alaskan crabs after exposure to freezing temperatures 
457 
were relatively similar in C. bairdi and C. opilio, then 
rose more quickly in C. opilio, reaching 100% at an 
exposure of -6°h. The results for crabs exposed at -10° 
and -20°C were nearly identical. Large proportions 
of the total mortality values for both C. bairdi and C. 
opilio occurred within 24 hours and then continued in 
a near linear pattern until the end of the 9-day holding 
period (Fig. 4). First-day mortality was especially high 
in C. opilio, accounting for more than 60% of the total 
mortalities observed. Eighty percent of mortality was 
observed by day 5 and day 6 for C. opilio and C. bairdi, 
respectively. 
Exposure to freezing temperatures resulted in sub- 
stantial impairments of reflex actions, both immediately 
after removal from the freezer (index A) and after the 
2-minute warming period in a water bath (index B). 
However, preliminary analyses showed that index B 
had two critical limitations in terms of association with 
subsequent crab mortality. First, 32-35% of crabs with 
apparently perfect reflex scores (index B = 0) died over 
the following 9 days. Second, mortality in C. opilio 
reached 100% at all impairment scores greater than 1. 
Figure 4 
Cumulative percentage of total mortality for Chionoecetes 
bairdi (Tanner crab) and C. opilio (snow crab) over time 
after exposure to freezing conditions. Total numbers 
of C. bairdi and C. opilio dying over the course of the 
experiment were 54 (54% of 100 tested) and 62 (60.8% 
of 102 tested), respectively. 
These flaws make index B a weak predictor of mortality, 
and this impairment index was considered no further. 
The results from index A were far superior. Mortality 
increased smoothly from an impairment of 0 to 6 in 
both species, and relatively little mortality occurred 
with an index value of 0. All of the following results 
are reported with respect to index A. 
Reflex impairment score increased in a near linear 
pattern with increasing exposure to freezing tempera- 
tures (Fig. 5). For both C. bairdi and C. opilio, mean 
impairments were just above 0 with an exposure of -2°h 
and increased steadily to 5.5 and 6.0 (loss of all reflexes 
tested) at -10°h. The variation was remarkably small 
for C. opilio, although crabs in the two longest expo- 
sures conducted at -10°C (-6 and — 8°h) fell well below 
the curve for trials conducted at -20°C. The effect of the 
test temperature on impairment was significant for C. 
opilio (ANOVA, P<0.001), but not for C. bairdi (P= 0.435). 
Patterns occurred with reflex impairments. The most 
sensitive reflex, lost first in 40% or more cases, was the 
ability to close chelae (Table 4). Kick and eye retraction 
were also lost first in substantial numbers of crabs. Re- 
flex action of the mouth was least likely to be the first 
reflex lost, and among all of the losses observed this 
response was lost in just 0.4% ( C . bairdi) and 1.0% (C. 
opilio) of individuals with impairments scoring 1 to 5. 
All other reflexes were lost in substantial numbers for 
both species (Table 4). 
Reflex impairment (index A) was a good predictor 
of mortality for C. bairdi and C. opilio and was inde- 
pendent from test temperature and crab size (logistic 
regression). The most parsimonious model for C. bairdi, 
containing only a constant and reflex impairment, cor- 
rectly predicted 80.0% of the mortality and survival 
(Table 5), whereas the full model (with all variables) 
