271 
Estimation of discard mortality 
of sablefish ( Anopiopoma fimbria) 
in Alaska longline fisheries 
Email address for contact author: chns.lu nsford t at noaa.gov 
1 Auke Bay Laboratories 
Ted Stevens Marine Research Institute 
Alaska Fisheries Science Center 
National Marine Fisheries Service 
National Oceanic and Atmospheric Administration 
17109 Pt Lena Loop Rd. 
Juneau, Alaska 99801 
2 Present address: 
School of Aquatic and Fishery Sciences 
University of Washington 
Box 355020 
Seattle, Washington 98195 
Abstract — -Sablefish ( Anopiopoma 
fimbria) are often caught inciden- 
tally in longline fisheries and dis- 
carded, but the extent of mortality 
after release is unknown, which 
creates uncertainty for estimates of 
total mortality. We analyzed data 
from 10,427 fish that were tagged in 
research surveys and recovered in 
surveys and commercial fisheries up 
to 19 years later and found a decrease 
in recapture rates for fish originally 
captured at shallower depths (210— 
319 m) during the study, sustaining 
severe hooking injuries, and sustain- 
ing amphipod predation injuries. The 
overall estimated discard mortality 
rate was 11.71%. This estimate is 
based on an assumed survival rate 
of 96.5% for fish with minor hooking 
injuries and the observed recapture 
rates for sablefish at each level of 
severity of hook injury. This esti- 
mate may be lower than what actu- 
ally occurs in commercial fisheries 
because fish are likely not handled as 
carefully as those in our study. Com- 
paring our results with data on the 
relative occurrence of the severity of 
hooking injuries in longline fisheries 
may lead to more accurate account- 
ing of total mortality attributable to 
fishing and to improved management 
of this species. 
Manuscript submitted 4 October 2011. 
Manuscript accepted 22 February 2012. 
Fish. Bull. 110:271-279 (2012). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Megan M. Stachura' 2 
Chris R. Lunsford (contact author) 1 
Cara J. Rodgveller 1 
Jonathan Heifetz' 
For stock assessment, accurate ac- 
counting of discard mortality is impor- 
tant for estimating total mortality 
attributable to fishing. Studies of 
sablefish ( Anopiopoma fimbria) and 
other fish species show that catch- 
related injuries can cause delayed 
mortality after a fish is discarded. 
For example, sablefish laboratory 
experiments have shown that the 
level of physical injury, reflex impair- 
ment, and behavior impairment may 
be useful proxies for delayed mortal- 
ity (Davis, 2005; Davis and Ottmar, 
2006). Pacific halibut ( Hippoglossus 
stenolepis) with more severe hook 
injuries had increased mortality and 
reduced growth compared to those 
with less severe injuries (Kaimmer, 
1994; Kaimmer and Trumble, 1998) 
and were visually impaired after 
exposure to simulated sunlight (Brill 
et ah, 2008). For Atlantic cod ( Gadus 
morhua L), injuries to the eyes, gills, 
and belly were more lethal than 
injuries to other anatomical parts 
(Palsson et ah, 2003). After release, 
Atlantic cod had inhibited activity 
for 4 days, during which there was 
potentially increased susceptibility to 
predation and delayed mortality (Neat 
et ah, 2009). 
A first step in estimating discard 
mortality is to estimate the propor- 
tion of fish that die after being dis- 
carded. Estimates of sablefish discard 
mortality rates and the derivation 
methods for determining these esti- 
mates vary regionally and by man- 
agement agency. In the southeast 
Alaska sablefish stock assessment 
conducted by the Alaska Depart- 
ment of Fish and Game for state wa- 
ters, a 25% discard mortality rate in 
the Pacific halibut longline fishery 
is assumed for sablefish (Dressel 1 ). 
For both trawl and longline federal 
groundfish fisheries in Alaska, 100% 
mortality is assumed for all sablefish 
that are discarded (Hanselman et al., 
2010). In the federal Pacific Coast 
sablefish stock assessment a much 
lower discard mortality rate of 10% 
is assumed for longline gear (Schir- 
ripa, 2008). 
Sablefish support one of the most 
valuable fisheries in Alaska (Hiatt et 
ah, 2010). The fixed gear fishery in 
1 Dressel, S. C. 2009. 2006 northern 
southeast inside sablefish stock assess- 
ment and 2007 forecast and quota. Fish- 
ery Data Series 09-50, 78 p. Alaska 
Dep. Fish Game, Anchorage, AK. 
