Yochum et at. A comparison of methods for evaluating mortality of discarded Cancer magister 
137 
n 
2 
Q 
O 
i 
c 
o 
-O 
c 
o 
o 
A Lab study-RB m Lab study-RS 
Cl < C2 
Cl = C2 
Cl >C2 
■c 
o 
A Lab study-RB 
a Lab study-RS 
O) 
o 
Cl < C2 
Cl = C2 
Cl > C2 
♦ Tag release events-RB O Lab study-CO 
A Lab study-RB 
Figure 6 
The relative short-term survival rates of Dungeness 
crabs (Cancer magister) collected off Oregon between 
February 2012 and April 2014 and classified as condi¬ 
tion 2 (C2: reflex impairment score >0) or as condition 
1 (Cl: score=0) for tag release events and the labora¬ 
tory holding study by fishery (commercial ocean fishery 
[CO] and recreational fisheries in Yaquina Bay, by boat 
[RB] and shoreside [RS]). (A) females, (B) hard-shell 
males, and (C) soft-shell males. Hard- and soft-shell 
females were combined owing to low numbers of the 
latter caught and, therefore, held or tagged). Note that 
the upper confidence limit (2.07) for the first RB tag re¬ 
lease event for hard-shell males exceeded the axis rule. 
Recreational fisheries Patterns in tag-return data from 
the recreational bay fishery from a boat are similar to 
mortality rate patterns from the laboratory-holding 
study for this fishery in that reflex impairment score 
and shell hardness were weak predictors, and rates 
were lower than those of the other fisheries. For the 
laboratory study, the most important predictor of de¬ 
layed mortality was whether or not the crab had any 
missing reflexes (a binary response). Mortality rates 
for crab were statistically indistinguishable by the lev¬ 
el of impairment. However, modeling outcomes for this 
fishery could have been influenced by the low numbers 
of crab with missing reflexes and the high proportion 
of hard-shell males caught, and, therefore, held in cap¬ 
tivity, which had a higher survival rate than females 
and soft-shell crab from the commercial fishery. Also 
similar to trends in the laboratory study, noninjured 
crab had a higher return rate than injured crab. How¬ 
ever, the significance of the relationship between the 
probability of tag return and injury was difficult to 
measure given the small number (35) of injured crab 
that were tagged and released. As in the commercial 
fishery, patterns in tag returns suggest that carapace 
width and sex may also have influenced return rates 
with this fishery. The frequency of returns was higher 
for crab with larger carapaces compared with the size 
frequency of those tagged. Also, overall return rates 
for females were lower than those for males. Although 
this result could reflect reduced survival for females 
that went undetected in the laboratory-holding study, 
it could also be indicative of a bias caused by fishermen 
and attributable to the sex of the crab. As they do with 
small crab, fishermen instinctually discard females 
without much inspection, while males are measured to 
determine their legal status. In measuring the crab, 
fishermen have more opportunities to observe the tag. 
Mortality rates were not estimated for the rec¬ 
reational shoreside fishery in the laboratory hold¬ 
ing study. However, Yochum et al. (2017) found that 
rates were likely more similar to those estimated for 
the commercial ocean fishery than the recreational 
bay fishery from a boat (Yochum et al., 2017). Tag re¬ 
turns for the recreational bay shoreside fishery, like 
the commercial sector, indicated that the probability of 
return is likely influenced by reflex impairment score, 
sex, shell hardness, and carapace width. This notion 
is consistent with laboratory findings, which indicated 
that mortality rates for the commercial ocean fishery 
could likely be applied to the shoreside fishery. With 
respect to bias, as with other fisheries, return rates 
were higher for larger crab. There were no clear tem¬ 
poral patterns; however, sample sizes were small for 
each release event. 
Efficacy of tag-return methods for research on discard 
mortality 
There are limitations when using tag-return methods 
to evaluate discard mortality for a low-impact fishery 
(i.e., one where, for the majority of animals, the stress- 
