Moiseev et al: Effects of pot fishing on the physical condition of Chionoecetes opilio and Chionoecetes bairdi 
243 
Figure 8 
Light micrographs of normal gills in snow crab (Chionoecetes opilio) and south- 
ern Tanner crab (C. bairdi) from our study of the effects of pot fishing on the 
physical condition of these species: (A) distal part of lamellae in a southern 
Tanner crab and (B) apical part of lamellae in a snow crab. Hematoxylin and 
eosin staining was used. Abbreviations: pc=pillar cells; mc=marginal canal. 
Scale bar=100 pm. 
nushkin, 2011). Tallack (2007) investigated mortality 
of red deepsea crab ( Chaceon quinquedens) in different 
hauling conditions (i.e., crabs hauled every 24 h, after 
intervals of 4 or 8 days) and found that crab hauled 
to the surface every 24 h showed significantly greater 
mortality than crab retrieved after 4 or 8 days. 
In our study, experiments on snow and southern 
Tanner crabs, like all experiments described in the 
previous paragraph, were conducted as actual field 
operations with minimal control of external variables, 
including air exposure, changes in temperature, light, 
and physical injuries. In our experiments, mortality of 
crabs was induced by blood sampling. For example, in 
experiment 1, mortality was 20% for snow crab and 
24% for southern Tanner crab, and all the dead crabs 
that could be identified from their remains were crabs 
from which samples of blood were taken 1 or 2 times. 
This mortality most likely resulted from predation of 
amphipods (e.g., Orchomenella affinis ) that were at- 
tracted to the wounds caused by sampling. However, 
in experiment 3, mortality rates did not differ signifi- 
cantly between crabs from which samples of blood were 
taken (17%) and crab from which no blood samples 
were taken (15%). 
Another substantial source of crab mortality in our 
experiments was trauma associated with gear encoun- 
ters. Externally visible injuries to the carapace were 
found often in dead animals that had encountered gear. 
In all dead crabs, soft tissues were quickly eaten away 
by predatory amphipods. It can 
be assumed that, within the size 
range of crabs kept in the pots in 
our experiments (see the Materi- 
als and methods section), aggres- 
sive interaction between crabs and 
cannibalism were not significant 
factors in the mortality of ani- 
mals. Cannibalism in snow crab 
occurs only between individuals of 
significantly different sizes (Dutil 
et ah, 1997; Lovrich and Sainte- 
Marie, 1997). Our research on the 
attractiveness of dead crabs as 
bait showed that they did not at- 
tract individuals of their own spe- 
cies (senior author, unpubl. data). 
Therefore, mortality of crabs in 
our experiments was not a reliable 
indicator of the physiological dis- 
orders in crabs. Reversible physi- 
ological disorders did not result 
in death of the animals, and mor- 
tality of crabs often was caused 
by trauma from gear. During the 
course of our experiments in the 
field, the vitality of each crab was 
monitored with a VI. Vitality, or 
general health status of crabs, 
can be characterized subjectively 
by observing or testing behavioral or whole-animal re- 
sponses (reflex actions). The severity of physiological 
disorders in crabs is related directly to changes in vi- 
tality of crabs (Stoner, 2009, 2012). 
The haul and return of pots to the seabed caused 
shifts in the homeostasis of crabs, leading to changes 
in health status of the animals. In turn, the health sta- 
tus of the animals influenced their physical responses 
to stress. We used adult male snow crab and southern 
Tanner crab that had completed a terminal molt be- 
tween 1.5 years and a few months previously. There- 
fore, the vulnerability of animals in our research to 
external factors was less influenced by intrinsic vari- 
ables, such as processes of growth, maturation, or molt 
stage, than it would have been if we had used imma- 
ture or egg-producing female crabs. 
A temporary shift of physiological homeostasis in 
crabs caused by the process of pot hauling may be cor- 
rected by the natural regulatory capacity of an organism 
or by adaptive physiological responses. The investiga- 
tions on the mortality of snow crab in crab pots carried 
out by Ivanov and Karpinski (2003) revealed that crab 
weakened by frequent pot hauls could restore natural 
physiological conditions (i.e., locomotor activity and 
righting behavior) if the time intervals between suc- 
cessive pot lifts were increased. In their experiments, 
it was found that after 2 pot lifts at time intervals of 2 
days, the surviving crabs were greatly weakened. How- 
ever, the condition of animals improved significantly af- 
