Stachura et al Estimation of discard mortality of Anoplopoma fimbria in Alaska longline fisheries 
275 
Year 1990 
Depth: 270-319 m 
Depth: 320^119 m 
Severity of hook injury: moderate 
Severity of hook injury : severe 
Amphipod predation: s10% scale loss 
Amphipod predation: >10% scale loss 
Higher mortality 
Hig 
<■ 
Lower mortality 
0.5 1.0 1.5 
Effect on recapture rate 
2.0 
Figure 2 
Comparison of the effects of the variables in the final model on the recapture rate 
of tagged sablefish ( Anoplopoma fimbria). The effect on recapture (circle) is the 
exponent of the estimated parameter for the variable in the logistic regression 
and is the odds ratio: the odds of recapture of a fish in a category compared to 
the odds of recapture in the initial category of the categorical variable (year: 
1989; depth: 210-269 m; severity of hook injury: minor; amphipod predation: 
no predation). Horizontal lines are 95% confidence intervals for the estimate. 
ratio for the effect of severe hooking injuries < 1 , indicat- 
ing a significant negative effect on recapture (Fig. 2). 
Although only a small portion of the fish sampled suf- 
fered from amphipod predation, it significantly affected 
recapture and was included in the final mode! (Table 2). 
Fish with no observed amphipod predation had a higher 
rate of recapture (11.86%) than fish with <10% scale loss 
(8.44%) and fish with >10% scale loss (7.84%) owing to 
amphipod predation (Table 3). The 95% confidence inter- 
val of the odds ratio for the effect of less than or equal to 
10% scale loss was less than 1, indicating a significant 
negative effect on recapture (Fig. 2). However, there 
was a high amount of variability around the estimated 
parameter for the effect of >10% scale loss because of 
a low number of samples (Fig. 2). The majority of fish 
(51.06%) that were too severely injured to be tagged had 
suffered from amphipod predation, and only 11.09% of 
fish that were healthy enough to be tagged had suffered 
amphipod predation. 
In our study location of hook injury, fish length, and 
type of gear injury did not significantly affect recap- 
ture rates. Hook injuries were not in critical locations 
that would likely cause mortality alone. Most injuries 
were located on the cheek and upper and lower jaws 
(95.53%). There were a small number of fish observed 
that had hook injuries to other areas of the body (nose, 
throat, eye, gill; 4.47%) (Table 3). A wide range of fish 
lengths were included in our study, but length did not 
Table 2 
Significant effects included in the reduced logistic regres- 
sion model, where the response is whether a sablefish 
(Anoplopoma fimbria) was successfully recaptured after 
tagging. The overall variable significance was calculated 
by using a Wald chi-squared test. 
Variable 
t 
df 
P(>X 2 ) 
Intercept 
571.0 
1 
<0.001 
Year 
11.6 
1 
<0.001 
Depth (m) 
34.8 
2 
<0.001 
Severity of hook injury 
12.4 
2 
0.002 
Amphipod predation 
7.7 
2 
0.021 
have a significant effect on recapture rate. Injuries 
caused by the line and roller gear also did not have a 
significant effect on recapture rate. This result may be 
the consequence of low statistical power because few 
fish (5.58%) sustained injuries caused by gear other 
than hooks (Table 3). 
Survival rates 
The absolute survival rate of fish in each category of 
severity of hook injury was calculated with Equation 3 
