McAllister et al.: Using experiments and expert judgment to model catchability of Pacific rockfishes 
297 
to between 63% and 81% of the reference case values. 
The CVs for q gross for the different surveys decreased 
slightly when a was set to 1 and increased slightly 
when its input distribution mode and maximum were 
doubled (Table 6). 
The qgross values for the different surveys showed 
varying amounts of positive correlation, which resulted 
from the use of the same or very similar nets in all 
of these surveys and the captains prescribing highly 
correlated prior inputs as in the case of the AWII and 
Nor’Eastern nets (Table 10, Fig. 8 shows a high degree 
of similarity in the q net outputs for these two nets). The 
Qgross va l ues f° r the DFO groundfish survey nets showed 
the highest correlations with values up to about 0.96. 
The q aross for the U.S. triennial survey showed the low- 
est correlations with the other nets because of the high 
amount of uncertainty in the fraction of the population 
in this survey (correlations between 0.14 and 0.35). The 
QCS shrimp q gg also showed low correlations with the 
other surveys also because of the high uncertainty in 
the fraction of the population in this survey area. 
In our application, density functions for q gross were 
unimodal and in all instances positively skewed. Thus, 
a multivariate lognormal density function was formu- 
lated to summarize the joint prior density function for 
Qa,oss f° r fh e six survey time series used in the stock 
assessment. This multivariate density function was for- 
mulated using the posterior median and covariance out- 
puts from the WinBUGS (Tables 10 and 11). The prior 
results for q aross for six of the surveys were compared 
with posterior results for q gross from a stock assessment 
of Bristish Columbia bocaccio for which a noninforma- 
tive prior for q aross was used (Table 11). All posterior 
medians for q aross obtained from the stock assessment 
with noninformative priors for p, r ,. oss (Table 11) were in- 
side of the 95% Pis for the informative q gross prior (Table 
11). However, in most instances the posterior medians 
were larger than the prior medians, indicating that the 
stock assessment data tend to produce stock biomass 
values lower than those indicated by the q gross density 
function obtained in this study. 
Some key stock assessment quantities are also shown 
that were obtained with a noninformative prior and the 
informative q gross prior (Table 12). The posterior mean 
values for stock biomass at maximum sustainable yield, 
stock biomass in 2008, and replacement yield changed 
slightly with the use of the informative q gross prior. In 
contrast, the posterior CVs for the current stock bio- 
mass and replacement yield decreased substantially 
with the use of the informative prior for q gross . 
