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Table 1 
Definition of symbols for the indices, model parameters, and model variables used to determine trawl catchability for bocaccio 
( Sebastes paucispinis) off British Columbia. 
Symbol 
Description 
Indices 
pop 
entire fish population of interest that is potentially susceptible to capture by the survey gear of interest 
n 
trawl net type, e.g., in study l=the groundfish AWII used in the Department of Fisheries and Ocean’s groundfish 
trawl surveys, in study 2=the shrimp trawl, in study 3=the Nor’ Eastern used in the U.S. triennial groundfish 
trawl survey 
c 
interviewed captain 
s survey 
Model parameters 
q sross the parameter that scales the model-predicted population biomass to a trawl survey swept area biomass value 
<lnet 
the parameter that reflects the fraction of exploitable biomass within the path (i.e., between the trawl doors) of a 
given type of survey net that is on average captured by the net 
Q availability 
the fraction of total exploitable population biomass indexed by a given survey (the proportion of the population 
biomass in the survey area) 
Q trawlable 
the parameter that accounts for the potential average difference in rockfish density between trawlable and 
untrawlable areas and the fraction of the surveyed area that is trawlable 
s s 
f Ts 
a 
the fraction of total population biomass present in the survey area 
the fraction of the total survey area A that is trawlable. 
the ratio of target rockfish density in untrawlable to trawlable habitat. 
8 S 
the bias correction factor to account for the difference in fish density between trawlable and untrawlable bottoms 
and the fraction of a survey area that is trawlable 
It.s 
n areas 
a l 
swept area biomass obtained from trawl samples in the trawlable part of a survey area 
the number of surveyed areas in the range of an assessed fish population 
estimate of the percent of rockfish that would be near-bottom (within 3-4 fm of the bottom, i.e., the kill zone) as 
the vessel passed overhead (Fig. 3) 
a 2 
a 1.2,c 
proportion of off-bottom rockfish that “dive” into the kill zone (Fig. 3) 
proportion of fish going into path of the net and doors from those in the water column that are in the horizontal 
path of the net and the doors (Fig. 3) 
a 3,l,n 
fraction of distance between the trawl doors that is in the path of the sweeps and bridles but more than 6 m inside 
of the door path (Fig. 3; Table 3) 
a 3,2,n 
fraction of distance between the trawl doors that is in the path of the sweeps and bridles but not more than 6 m 
inside of the door path, i.e., the fraction of fish in the “dead zone” inside which all fish are deflected out of the path 
of the net (Fig. 3, Table 3) 
a 3.6.n,c,i 
fraction of fish between the doors that end up in front of the net depending on whether the interviewed captain 
included the “dead zone” in assessing this fraction (i = 1 means did not distinguish dead zone; i= 2 means did 
distinguish the dead zone) (Fig. 3) 
a 4.n 
relative proportion of fish remaining between the wingtips after excluding those in the deadzone (Fig. 3, 
Table 4) 
a 5,n 
a 6,n 
a 7.n.c 
a 8,n 
relative proportion of fish in the herding zone after excluding those in the deadzone (Table 4) 
proportion of the fish in front of the bridles and sweeps that would be herded into the path of the net 
Proportion of fish that are captured of those that end up in front of the net 
ratio of wingspread to doorspread used as a correction factor for q net in instances where the swept area estimate 
has been computed based on the distance between the trawl net wingtips 
U n , c 
Minimum threshold uncertainty factor (this factor could be made larger for net types with which a particular 
captain has had much less experience) 
Mo del va riables 
jSw.a. average empirical swept area biomass estimate for the trawlable substrate in area s from the years in which 
n yr,s 
survey took place in that area. 
number of years for which an estimate of swept-area biomass is available for a given survey in the reference year 
set 
lr s,i-J 
r -° b s,i-j 
SE s 
predicted natural logarithm of the ratio of net i to net j catchability 
observed ratio of density values from net i and net j for survey area s 
standard error in the mean of the natural logarithms of the swept-area biomass estimates in area s 
