451 
Abstract — Millions of crabs are 
sorted and discarded in freezing con- 
ditions each year in Alaskan fisheries 
for Tanner crab ( Chionoecetes bairdi ) 
and snow crab (C. opilio). However, 
cold exposures vary widely over the 
fishing season and among different 
vessels, and mortalities are difficult 
to estimate. A shipboard experiment 
was conducted to determine whether 
simple behavioral observations can 
be used to evaluate crab condition 
after low-temperature exposures. 
Crabs were systematically subjected 
to cold in seven different exposure 
treatments. They were then tested 
for righting behavior and six dif- 
ferent reflex actions and held to 
monitor mortality. Crabs lost limbs, 
showed reflex impairment, and died 
in direct proportion to increases in 
cold exposure. Righting behavior was 
a poor predictor of mortality, whereas 
reflex impairment (scored as the sum 
of reflex actions that were lost) was 
an excellent predictor. This composite 
index could be measured quickly and 
easily in hand, and logistic regression 
revealed that the relationship between 
reflex impairment and mortality cor- 
rectly predicted 80.0% of the mortality 
and survival for C. bairdi , and 79.4% 
for C. opilio. These relationships pro- 
vide substantial improvements over 
earlier approaches to mortality esti- 
mation and were independent of crab 
size and exposure temperature. 
Manuscript submitted 24 March 2009. 
Manuscript accepted 23 June 2009. 
Fish. Bull. 107:451-463 (2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Prediction of discard mortality for Alaskan crabs 
after exposure to freezing temperatures, 
based on a reflex impairment index 
Allan W. Stoner 
Fisheries Behavioral Ecology Program 
Alaska Fisheries Science Center 
National Marine Fisheries Service, NOAA 
2030 S Marine Science Drive 
Newport, Oregon 97365 
Email address for author: al.stoner@noaa.gov 
Fishes and invertebrates are dis- 
carded from fishing operations in ever 
increasing quantities (Alverson et al., 
1994; Cook, 2003; Broadhurst et al., 
2006), and the various components 
of bycatch-related mortality, includ- 
ing detected, undetected, immedi- 
ate, and delayed forms of mortality 
have been discussed in recent reviews 
(Hall et al., 2000; Davis, 2002). Crabs, 
shrimps, and lobsters are discarded in 
high proportions in relation to land- 
ings in both the directed fisheries 
for crustaceans and in the prosecu- 
tion of finfish fishing (Cook, 2003), 
and many of those discards die from 
stressors including physical injuries to 
the carapace, lost and broken limbs, 
and physiological stress associated 
with temperature changes and air 
exposure. 
Davis (2002) reviewed general prin- 
ciples of bycatch-related stressors and 
concluded that some aspects of han- 
dling and discard mortality can be 
simulated in the laboratory. This sim- 
ulation has been undertaken exten- 
sively for fishes in recent years (see 
Davis, 2002), and controlled labora- 
tory exposures to stressors relevant 
to fishing, such as air exposure and 
dropping of crabs (during handling 
on ships), have been conducted for 
lobsters (Brown and Caputi, 1983; 
DiNardo et al., 2002; Harris and 
Ulmestrand, 2004) and crabs (Zhou 
and Shirley, 1995; Grant 2003). Field 
studies designed to test different han- 
dling methods for discards typically 
employ either a tag and recovery 
approach (Brown and Caputi, 1983; 
Watson and Pengilly, 1994) or some 
means of holding the test animals 
in field enclosures (Kennelly et al., 
1990; Grant, 2003; Broadhurst et 
al., 2009) or tanks (DiNardo et al., 
2002; Stoner et al., 2008). Although 
direct experimental observations on 
mortality are useful, tag studies of- 
ten yield relatively low returns, and 
experiments requiring holding can 
ordinarily accommodate only a rela- 
tively low number of treatment types 
and limited replication. 
As an alternative to observing mor- 
tality directly it is sometimes possible 
to apply a measure of animal condi- 
tion that is closely associated with 
delayed mortality. For example, Shir- 
ley and Stickle (1982) suggested that 
righting behavior (i.e., an animal’s 
ability to turn from a ventrum-up 
position to normal orientation) is a 
complex reflex requiring muscle co- 
ordination and neurological control 
that can be a sensitive measure of 
well-being. Righting behavior has 
been observed in several studies with 
Alaskan crabs (Stevens, 1990; Carls 
and O’Clair, 1995; Zhou and Shir- 
ley, 1995; Warrenchuk and Shirley, 
2002), and others have scored vitality 
of crabs on the basis of spontaneous 
movements of the appendages in order 
to predict delayed mortality (Stevens, 
1990; Purves et al., 2003). More re- 
cently, Stoner et al. (2008) developed 
an extension of the vitality metric, 
exploring a suite of six reflex actions 
(Table 1) that reflect the condition of 
Chionoecetes bairdi (Tanner crab) and 
C. opilio (snow crab) injured in bot- 
tom trawl operations. These reflexes 
are stereotypic and can be evaluated 
rapidly in the tester’s hand (out of 
water) during shipboard operations, 
