Stachura et al. : Estimation of discard mortality of Anoplopoma fimbria in Alaska longline fisheries 
273 
135°W 130°W 
Figure I 
Map of the areas in Southeast Alaska where sablefish (Anoplopoma fimbria) were tagged 
during research surveys in 1989 (•) and 1990 ( + ). 
model fit. The model with the minimum Akaike infor- 
mation criteria (AIC) value was chosen. A Wald chi- 
squared test was used to calculate the overall signifi- 
cance of categorical variables with multiple coefficients. 
All statistical analysis was implemented in R software, 
vers. 2.11.1 (R Development Core Team, 2010) including 
use of the aod package, vers. 1.2 (Lsenoff and Lancelot, 
2010 ). 
Recapture rates for categories within each variable 
were calculated by dividing the number of recaptured 
fish by the number of tagged fish for each category. 
Absolute survival rates were calculated for each level of 
hook severity on the basis of observed recapture rates 
and the survival rate of a Pacific halibut with minor 
hooking injuries (Kaimmer, 1994; Kaimmer and Trum- 
ble, 1998; Trumble et. al., 2000). Previous studies have 
determined that the expected survival of a properly 
handled Pacific halibut is in the 95-98% range; a re- 
leased fish with minor injuries has an estimated 96.5% 
survival rate (Trumble et al., 2000). We used the Pacific 
halibut estimate of survival rate as a proxy for that of 
sablefish for the following reasons: these species do not 
experience barotrauma as a result of rapid decompres- 
sion; they co-occur in the same water temperatures, 
areas, and depths; they are caught with nearly identical 
gear types; and they are commonly fished by the same 
fishing vessels and crew. Like Pacific halibut, sablefish 
are hardy and, when handled appropriately, have high 
survival rates after capture and discard. Long-term tag- 
ging programs for both species provide evidence of their 
hardiness (Kaimmer, 2000; Maloney 2 ). The hardiness 
of sablefish is also supported by previous research in a 
laboratory setting where there was 100% survival after 
60 days (Davis et al., 2001). Ours is the first dedicated 
study to estimate sablefish discard mortality. Previous 
estimates of Pacific halibut survival rates are the best 
available data to use as a proxy for sablefish. 
The average survival rate of fish with different severi- 
ties of hook injury, i.e., the absolute survival rate, was 
estimated on the basis of recapture rates and relative 
frequency of all 3 levels of hook injury (minor, moderate, 
severe) by using the methods in Kaimmer and Trumble 
(1998). The overall absolute survival rate (S) of cap- 
tured fish was calculated with the following formula: 
S = 
( R 0 + R 1 +R 2 ) 
{Tc + ^+T.t + NT j 
Ro 
To 
x 0.965, 
( 2 ) 
where T 0 , T v and T 2 and R 0 , R ,, and R 2 are the number 
of fish tagged ( T ) and recovered (R) with minor (0), mod- 
erate (1) and severe hook injuries (2). Fish that were not 
