454 
Fishery Bulletin 107(4) 
Table 2 
Summary of exposures of crabs to freezing temperatures: Chionoecetes bairdi (Tanner crab) (80-100 mm carapace width [CW]) 
and C. opilio (snow crab) (71-100 mm CW). Treatments are expressed in degree-hours (°h) — the product of temperature (in 
degrees Celsius) and time (in hours). Values for actual temperature and time of exposure are reported as means and standard 
deviations. Ten crabs were tested in each treatment, except for the -8°h exposure for C. opilio at -20°C where 12 crabs were 
tested. 
Nominal 
temperature 
(°C) 
Exposure 
treatment 
(°h) 
C. bairdi 
C. opilio 
Actual 
temperature 
(°C) 
Exposure 
time 
(min) 
Actual 
temperature 
(°C) 
Exposure 
time 
(min) 
-20 
-2 
-17.6 ±3.1 
7.3 ±1.8 
-17.2 ±3.7 
7.3 ±1.8 
-3 
-17.6 ±2.2 
10.5 ±1.5 
-17.0 ±2.9 
10.5 ±1.9 
-4 
-17.0 ±2.8 
14.5 ±2.8 
-16.6 ±2.9 
14.8 ±2.4 
-5 
-19.0 ±1.6 
15.8 ±1.2 
-17.8 ±3.1 
17.2 ±3.4 
-6 
-18.2 ±1.8 
20.0 ±2.2 
-16.6 ±2.3 
22.2 ±3.3 
-8 
-19.6 ±0.5 
24.2 ±0.5 
-17.2 ±2.4 
28.6 ±4.3 
-10 
-16.3 ±3.5 
40.8 ±9.3 
-17.0 ±2.5 
36.6 ±4.4 
-10 
-2 
-10.0 ±0.7 
12.0 ±0.7 
-10.2 ±0.5 
12.0 ±1.6 
-6 
-11.0 ±0.7 
33.0 ±2.0 
-10.6 ±0.5 
33.6 ±1.2 
-8 
-10.4 ±0.5 
46.4 ±2.1 
-10.4 ±0.5 
46.4 ±2.0 
of cold-related stress that would result in a full range 
of impairments (0 to 6; see below). Mortality in C. 
bairdi observed by Carls and O’Clair (1990) increased 
in a clear sigmoid pattern from 0% to 100% with in- 
creasingly severe exposures from approximately -2 to 
-7°h. Therefore, exposures of -2, -3, -4, -5, -6, -8 
and — 10°h were chosen for this study. These exposures 
were achieved with two nominal temperatures, -20°C 
for primary experiments, and additional tests at — 10°C 
to test for the generality of the degree-hour approach 
(Table 2). Temperature excursions of 1-3°C sometimes 
occurred during a run, particularly when the largest 
crabs were placed in the small freezer, but the degree- 
hour exposure desired could be easily achieved by sys- 
tematically increasing or decreasing exposure time for 
an individual run. 
Experimental protocol 
Crabs for this study were held for at least 48 h before 
initiating experiments on cold stress. Each crab was 
inspected for injury and retested for reflexes just before 
experimentation to insure that only crabs in perfect 
condition were used. In fact, few crabs in diminished 
condition were found among those initially selected for 
holding (<1%), indicating that the holding environment 
was suitable. 
Experiments were typically conducted with pairs of 
crabs. This procedure ensured that exposures to freez- 
ing temperatures and subsequent handling for each crab 
could follow a strictly timed protocol, and that uniform 
postexposure testing was possible. First, the test crabs 
were marked with uniquely numbered vinyl spaghetti 
tags tied securely but loosely around the basi-ischium 
of the third or fourth leg. The crabs were then quickly 
placed on the freezer rack (at a preset temperature), 
ventrum up to prevent excessive movement. Tempera- 
ture of the freezer was closely monitored during the 
exposure, and exposure times were adjusted to main- 
tain the prescribed degree-hour treatment. The seven 
different exposures were interspersed over the course 
of runs made at each experimental temperature (-20° 
and -10°C) until 10 or 12 replicates of each exposure 
were completed (Table 2). 
After exposure to the cold each crab was evaluated 
with a series of three basic tests of behavioral capabili- 
ties. 1) Immediately following removal from the freezer 
the crab was tested for the presence or absence of the 
six reflex actions (Table 1). 2) Then, the crab was laid 
ventrum up in a flowing seawater bath (dimensions = 
80x50x30 cm deep; 8-9°C) and observed for 120 sec- 
onds. Attempts by the crab to turn dorsum up were 
recorded, and if it was successful the time to right was 
recorded. This procedure was identical to that used by 
Carls and O’Clair (1990). Although crabs placed in this 
position in the freezer normally lay quietly, the natural 
tendency of crabs in water is to quickly turn dorsum up. 
3) After precisely 120 sec in the water bath, the crab 
was removed from the water and reflex actions were re- 
tested. After these tests, any autotomies were recorded 
(identifying the specific limbs missing), and the crab 
was returned to a large recovery tank for monitoring of 
mortality. Mortality was assessed and dead crabs were 
removed each day until the end of the experiment when 
reflexes were re-assessed for all of the living crabs. 
Autotomies were recorded for dead crabs and for all 
live crabs at the end of the experiment. Tests for the 
two species spanned six days, and each individual was 
