Rose et al Mortality rates for Ch/onoecetes opiiio, C. bairdi, and Parahthodes camtschaticus after trawls on the seafloor 
49 
□ No reflexes missing 
a No reflexes missing + injury (RKC) 
□ Some reflexes missing (1-5) 
m All 6 reflexes missing 
0% 
10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 
Snow crab 
Control 
Sweep 
Footrope center 
Footrope wing 
Tanner crab 
Control 
Sweep 
Footrope center 
Footrope wing 
Red king crab 
Control 
Raised sweep 
Sweep 
Footrope center 
Footrope wing 
t: .i it 
n=m 
Figure 3 
Percentage of crabs that displayed a range of reflex states in our study of unobserved mortality rates 
for snow crab (Chionoecetes opiiio), southern Tanner crab (C. bairdi), and red king crab (Paralithodes 
camtschaticus) . Reflex states were assigned on the basis of the number of reflexes that were missing; 
6 reflexes were assessed. Crabs were captured after they contacted 1 of the 3 components of a bottom 
trawl representative of the gear used in Bering Sea bottom trawl fisheries — the center of the footrope, 
the footrope wings or extensions, or the sweep — or, for red king crab only, a sweep raised off of the 
seafloor (Rose et al., 2010). Crabs were captured with no gear contact during control tows. Injured red 
king crab with no missing reflexes were categorized separately. RKC = red king crab. 
nificantly lower for crabs that encountered the sweeps 
than for those crabs that encountered the footrope and 
were higher for those crabs that encountered the wing 
portion of the footrope as opposed to the center foo- 
trope. Although the mortality rates for the southern 
Tanner and snow crabs were similar, both had lower 
mortality rates than did the red king crab for all trawl 
components. Raising the sweeps with widely spaced 
disk clusters reduced red king crab mortality from 10% 
to 4%. 
Holding only samples of the large numbers of crabs 
with no missing reflexes (no missing reflexes and unin- 
jured for red king crab) greatly reduced the number of 
held crabs and produced minimal effects on precision 
of the mortality estimates. For example, the confidence 
interval estimation process was run with a sample size 
of 2581, representing all such red king crab observed, 
instead of the 367 crabs actually held. The resulting 
confidence range (high limit to low limit) for foot- 
rope wing mortality was reduced only from 14.25% to 
13.99% by holding 7 times as many crabs. Confidence 
ranges for footrope center and sweep mortalities were 
reduced even less (3.53% to 3.50% and 5.98% to 5.95%, 
respectively). 
Logistic regression was used to examine whether 
mortality rates varied by species, sex, size, and shell 
condition, after the effects of gear were removed. Near- 
ly all crabs had either a new hard shell or old shell. 
For southern Tanner and snow crabs, marginally signif- 
icant effects were detected between species, sexes, and 
sizes. When the mean effects across the combinations 
of those factors were examined, it was apparent that 
most of those effects were the result of higher mortali- 
ties for snow crab with carapace widths >95 mm; those 
large snow crab were nearly all males. Large snow crab 
were approximately twice as likely to die as smaller 
