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Fishery Bulletin 107(4) 
test equivalent in this new study (-2°h) resulted in no 
mortality. Van Tamelen (2005) pointed out that simple 
wind chill estimates are not particularly useful in the 
context of heat exchange for crabs and he developed a 
thermal model for C. opilio that accommodates crab size 
and incorporates the numerous elements of chilling, such 
as convection, radiation, evaporation, and conduction. 
Air exposure itself probably did not cause death. Ear- 
lier observations indicate that both C. bairdi and C. 
opilio are highly tolerant of handling and air exposures 
above freezing (Macintosh et ah, 1996; Grant, 2003). 
For example, McLeese (1968) observed no mortality in 
C. opilio after 4-day exposures to air in two above-freez- 
ing temperatures (3° and 8°C). Stevens (1990) reported 
a median lethal holding time of 8.3 hours in air for C. 
bairdi, and preliminary experiments at the Kodiak Labo- 
ratory (Stoner and Munk, unpubl. data) showed that C. 
bairdi could recover and survive for months after air ex- 
posures (15— 18°C) up to seven hours. Although it is pos- 
sible that mortality was caused by impaired oxygen de- 
livery because of freeze-damaged gills, Carls and O’Clair 
(1995) argued convincingly against that mechanism, and 
Warrenchuk and Shirley (2002) proposed that mortality 
associated with freezing temperatures was caused by 
neurological damage. Their conclusion arose from obser- 
vations of jerky, uncoordinated, and uncontrolled motions 
that would indicate nerve damage. Crabs in this study 
also commonly presented the same symptoms. 
Autotomy 
Shedding damaged limbs (autotomy) is an adaptation 
triggered by stress detectors in the limbs of crustaceans 
to prevent blood loss (Wales et al., 1971). The long, 
narrow form of the walking legs results in relatively 
rapid cooling (van Tamelen, 2005), and autotomy is com- 
monly observed in Chionoecetes spp. exposed to freezing 
temperatures. In the present study, autotomy increased 
with increasing cold exposure, especially in C. opilio — a 
reaction analogous to that of earlier experiments with 
Alaskan crabs (Carls and O’Clair, 1995; Warrenchuk 
and Shirley, 2002). The proportions of types of limbs 
lost varied substantially between the two subject spe- 
cies for unknown reasons; however, the distribution of 
losses by C. opilio was similar to observations reported 
by Warrenchuk and Shirley (2002) who noted the rela- 
tively rare loss of chelipeds. 
Delays in limb autotomy appear to be common among 
crabs and may have important consequences. As with 
the present study, others have observed that limb loss 
continues in holding tanks after exposure to cold tem- 
peratures (Carls and O’Clair, 1995; Warrenchuk and 
Shirley, 2002). The problem is exacerbated when limb 
losses increase during subsequent molting cycles (Carls 
and O’Clair, 1995). Given the apparent delays in autot- 
omy, it is likely that limb losses observed before discard 
in typical fishing operations are substantially lower 
than the actual number. Autotomy may be especially 
critical for crabs that have reached a terminal molt or 
that molt infrequently. For example, C. opilio >90 mm 
CW appear not to regenerate limbs, and smaller crabs 
do so slowly, over at least two molt cycles (Miller and 
Watson, 1976). Therefore, Warrenchuk and Shirley 
(2002) considered autotomy to be a permanent injury 
for large C. opilio, and multiple limb losses create an 
obvious impediment for crabs returning to the bottom 
with regard to feeding, predator avoidance, reproductive 
behavior, and other ecological functions (see below). 
Behavioral and reflex predictors of mortality 
Righting ability depends upon a complex integration 
of neurological and mechanical systems, and several 
biologists have suggested that this may be a good con- 
dition index for Alaskan crabs (Stevens, 1990; Carls 
and O’Clair, 1995; Zhou and Shirley, 1995). As earlier, 
crabs demonstrating positive righting results in this 
study survived in high proportion. However, righting 
was a poor predictor of mortality because more than 
half of surviving crabs (both species) made no attempt 
to right. Also, Warrenchuk and Shirley (2002) found 
that the ability of crabs to right often recovered after 
several days. Although Stevens (1990) suggested that 
the time required to right might provide a useful pre- 
dictor of survival, no such association was found in this 
study. Observation of righting behavior has two further 
limitations for assessing crab condition. First, because 
exposure to freezing temperatures and other forms of 
injury frequently result in autotomy, righting ability 
can be impaired by the lack of certain limbs. Second, the 
use of tanks of water to observe righting behavior on a 
moving vessel can be difficult or impractical. 
Various other indicators have been used to assess the 
condition of crustaceans toward the goal of predicting 
survival or mortality. Stevens (1990) evaluated the 
vitality of Alaskan crabs, scoring them as alive and 
active, moribund, or dead. Purves et al. (2003) used 
a similar three-tier index of vitality (i.e., lively, limp, 
or dead) in three lithodid crabs ( Paralomis spp.) to 
evaluate how different fishing modes used in the South 
Atlantic toothfish ( Dissostichus eleginoides) fishery af- 
fect the bycatch mortality of crabs. Criteria for the 
index incorporated four reflexes, namely actions by the 
mouth parts, chelae, and legs, and leg flare. Therefore, 
the vitality index used by Purves et al. (2003) could 
have been expanded to a reflex impairment score with 
five increments (0-4) instead of just two for live crabs. 
The reflex impairment score reported in this study 
was based upon the same principle of considering each 
reflex independently and providing a seven-increment 
resolution (0-6). 
Davis (2007) and Stoner et al. (2008) discussed the 
merits of using multiple reflexes and a higher resolu- 
tion for a reflex impairment index to predict discard 
mortality. One advantage is that the composite score 
reflects animal condition and the likelihood of survival 
over a wide range of stressor types and environmental 
exposures (i.e., physiological stress as well as physical 
injuries). This result is true because different forms of 
stress can have different impacts on the reflexes tested, 
