278 
Fishery Bulletin 1 10(2) 
and Clarence Straits; Dressel 1 ), and the assumed 100% 
mortality of sablefish caught in other target fisheries 
in federal waters in Alaska (Hanselman et ah, 2010). 
Applying the 11.71% mortality rate to the average 
catch of sablefish discarded in federally managed hook- 
and-line fisheries (491 t, 2004-09 average; Hanselman 
et al., 2010), yields an annual discard mortality of 
57.5 tons. 
There are two reasons why our estimate of absolute 
discard mortality may be lower than what occurs in 
the commercial fishery. First, in our study fish were 
handled carefully and released, whereas in commer- 
cial fisheries we would expect a greater proportion of 
moderate and severe injuries that would result in a 
higher discard mortality. Second, commercial fishery 
discards come from multiple fisheries that use numer- 
ous gear types, most notably different hook types and 
sizes. Larger hooks have been shown to result in higher 
discard mortality (Trumble et al., 2000). Because the 
halibut fishery in Alaska uses larger hooks than we 
used in our study, a higher discard mortality rate for 
sablefish would be expected in the halibut fishery. Care- 
ful hook removal during release of fish could potentially 
minimize discard mortality rates observed in commer- 
cial fisheries. 
Conclusion 
In this study we examined some of the factors that affect 
the discard mortality rate of sablefish in Alaskan long- 
line fisheries. We found a decrease in recapture rates for 
fish originally captured at shallower depths (210-319 m) 
in our study, sustaining severe hooking injuries, and 
sustaining amphipod predation injuries. Based on the 
severity of hook injury, we estimated an overall discard 
mortality rate of 11.71%. Obtaining data on the relative 
occurrence of the severity of hook injuries that occur in 
these fisheries is a logical next step. Such data would 
allow us to extrapolate our findings more reliably and 
may lead to a more accurate accounting of total mortal- 
ity attributable to fishing and to improved management 
of this species. 
Acknowledgments 
This analysis was performed while author M. Stachura 
was a student intern from the University of Miami and 
funded by the National Oceanic and Atmospheric Admin- 
istration (NOAA) Ernest F. Hollings Undergraduate 
Scholarship Program administered by Oak Ridge Associ- 
ated Universities through a Cooperative Grant sponsored 
by NOAA. We thank N. Maloney for managing the tag 
data for the entirety of this project. We also thank E. 
Varosi and J. Fujioka for help in designing hook injury 
codes, and the crew of the RV Townsend Cromwell. This 
manuscript has benefited from review by D. DiResta, G. 
Thomas, J. Richardson, J. Murphy, K. Echave, P. Rigby, 
and three anonymous reviewers. 
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