293 
AbStraCt.-Between 1986 and 1988, 
10,545 double-tagged sablefish were 
released off California, Oregon, and 
Washington. Tags recovered from these 
fish have provided one of the best sets 
of data available for estimating tag- 
shedding rates. We developed a new 
model and a maximum-likelihood pro- 
cedure to estimate the rates. Both ini- 
tial and long-term shedding rates were 
low, but posteriorly placed tags were 
shed at about twice the rate of anteri- 
orly placed tags. Bootstrapping indi- 
cated that the estimates were precise 
and accurate. Shedding rates for sable- 
fish were considerably lower than most 
published estimates for other species. 
Although the rates were low, the extra 
tag increased recoveries by nine percent 
over a six-year period. 
Manuscript accepted 13 September 1996. 
Fishery Bulletin 95:293-299 f 1997). 
Estimates of tag loss from 
double-tagged sablefish, 
Anoplopoma fimbria 
William H. Lenarz 
Tiburon Laboratory 
National Marine Fisheries Service, NOAA 
3150 Paradise Drive, Tiburon, California 94920 
E-mail address: billl@tib.nmfs.gov 
Franklin R. Shaw 
Alaska Fisheries Science Center 
National Marine Fisheries Service, NOAA 
7600 Sand Point Way NE, Seattle, Washington 981 I 5-0070 
The sablefish, Anoplopoma fimbria 
(Pallas, 1811), is a long-lived spe- 
cies (Beamish and McFarlane, 
1987) of considerable commercial 
importance (Kinoshita, 1987; Kor- 
son and Kinoshita, 1989; Kinoshita 
et al., 1996) and is found in the 
north Pacific Ocean from Baja Cali- 
fornia, north to the Bering Sea, and 
south to Japan in the western Pa- 
cific (Sasaki, 1985). Scientists have 
used tagging to study population 
size, mortality, migration, and 
movement of this species for more 
than four decades (Holmberg and 
Jones, 1954; Wespestad et al., 1983; 
Beamish and McFarlane, 1988; 
Fujioka et al., 1988; Heifetz and 
Fujioka, 1991). 
Estimates of mortality and exploi- 
tation rates, along with estimates 
of population size, can be biased 
owing to loss or shedding of tags 
(Wetherall, 1982). Estimated rates 
of tag loss are used to correct the 
bias. The placement of two tags in 
the same fish (double-tagging) is the 
most common technique used to 
obtain data for estimation of tag loss 
rates (Beverton and Holt, 1957; 
Gulland, 1963; McFarlane et al., 
1990). In this study we estimate the 
rate of tag loss from sablefish, us- 
ing results from a double-tagging 
experiment. 
Methods 
Sablefish were captured with fish 
traps (Parks and Shaw, 1994), 
double tagged, and released by the 
Alaska Fisheries Science Center 
(AFSC) during 1986, 1987, and 
1988. The Southwest Fisheries Sci- 
ence Center (SWFSC) used bottom 
trawl gear (Butler et al., 1989) to 
capture additional sablefish for 
double tagging in 1987. Identical 
tags and tagging procedures were 
used during the three years. 
Captured sablefish were rou- 
tinely put into “live” tanks supplied 
with fresh-running seawater imme- 
diately after the catch was brought 
on board (Shaw, 1984). No anes- 
thetic was used. Usually within 15 
minutes of the completion of each 
haul, sablefish were dip-netted from 
the live tank and placed in a pad- 
ded tagging cradle. Each sablefish 
was tagged with two identical an- 
chor tags (Floy FB-68). Tags were 
60 mm long, 2 mm in diameter, yel- 
low in color, and labeled with a 
unique number and with instruc- 
tions on where to return the tag. 
The primary tag was placed below 
the anterior end of the first dorsal 
fin, and the secondary or extra tag 
was placed near the posterior end 
of the same fin. Each tag was in- 
