104 
Fishery Bulletin 112(2-3) 
' 1200 
- 1000 
I 
- 800 
< 
CD 
<J > 
- 600 ~ 
c 
- 400 | 
- 200 
- 0 
1990 1995 2000 2005 2010 
Year 
Figure 2 
Population size and harvest levels for red king crab (Paralithodes 
camtschaticus ) in 1991—2012. Population size (in thousands of indi- 
viduals) is for the northeast section of the Kodiak district, as defined 
for the westward region trawl survey of the Alaska Department of 
Fish and Game, and harvest levels are for Chiniak Bay. The study 
area, Womens Bay, is part of Chiniak Bay, which is in turn part of the 
northeast section of Kodiak district (Fig. 1). Data used in this graph 
came from Alaska Department of Fish and Game reports on bottom 
trawl surveys of crabs and groundfishes conducted in 1991-2012: 
Technology Fishery Reports 93-16, 93-17 and Regional Information 
Report 4K95-1 by D. Urban, and Fishery Management Reports 05-48 
and 13-27 by K. Spalinger. 
pot is flipped over. Field personnel made observations 
on both ghost and actively fishing pots to determine 
the likely causes of pot loss in Womens Bay. Divers rou- 
tinely disabled all ghost pots that they discovered, ren- 
dering them incapable of catching animals, and they 
released all trapped animals. 
We assessed the effects of ghost fishing on the popu- 
lation of red king crab in Womens Bay by modeling the 
rate of tag loss. We assumed, on the basis of hundreds 
of hours of in situ observations during which we did 
not see any differences in behavior between tagged and 
untagged crabs, that tagged animals were representa- 
tive of the population (except in cases of handling mor- 
tality, which we quantified and explicitly corrected for) 
and that tagging did not change behavior (Pollock et 
al., 1991). In particular, in the context of this study, 
we assumed that tagged crabs did not suffer higher 
natural or fishing mortality, that they did not molt at 
a higher rate, and that they were no more likely to en- 
ter a crab pot than were untagged crabs. Given these 
assumptions, the mortality rate of the population as 
a whole would be similar to the calculated mortality 
rates of tagged crabs (Pollock et al., 1991; Lambert et 
al., 2006). 
As part of our determination of mortality rates, we 
estimated the number of days between the release date 
and date of final condition (e.g., the day a crab molted 
or died). If a tag had been located from the surface at 
the same position several times, then a dive was per- 
formed to determine the final condition of a crab. In 
most of these cases, we used the date from the second 
time the crab was located at that same position as the 
estimated date of final condition. When the time be- 
tween the surface locations was greater than a month, 
the date half-way between them was used. If there was 
no indication that the crab had remained in the same 
location for a length of time (fewer than 2 surface ob- 
servations at the same location), we used the day of the 
final dive observation as the end date. 
We fitted the data using maximum likelihood to an 
exponential loss model assuming a binomial distribu- 
tion such that 
P = e- rt , 
where P = the probability that a tagged crab molted, 
died, or was lost; 
/- = the instantaneous loss rate; and 
t = the time in days. 
We calculated the loss rate due to each cause (i.e., 
molting, ghostfishing mortality, handling mortality, or 
tag detachment, other mortality, and tag malfunction) 
with the proportional number of crabs in each category. 
For example, the rate of mortality from ghost fishing 
was calculated as 
