Rooper and Martin: Comparison of indices of abundance with biomass estimates from trawl surveys 
29 
from the commercial fishery, as well 
as biomass and age data from the 
bottom trawl survey to estimate the 
total size of the populations. In the 
Pacific ocean perch and rougheye and 
blackspotted rockfish time series, the 
habitat model-based indices of abun- 
dance were correlated with the pre- 
dicted survey biomass from the stock 
assessment model (Fig. 5). For Pacific 
ocean perch, the results were very 
good (r=0.95), whereas for rougheye 
and blackspotted rockfish the correla- 
tion was weaker (r= 0.67 ). This finding 
corroborates that the habitat model 
indices are consistent with the entire 
data set incorporated into the stock 
assessment, even though the habitat 
model indices do not necessarily track 
the interannual changes in biomass for 
these two species that was calculated 
with the stratified random sampling 
formulae of the bottom trawl survey. 
Although the model predicting 
rougheye and blackspotted rockfish 
LCPUE fitted reasonably well, there 
is no doubt that it could be improved 
by a clearer resolution of the two 
species. Because they are not easily 
identified in the field, even by biolo- 
gists trained to distinguish them, it 
is not clear that the two species are 
found in the same habitats throughout 
their distributions. If the two species 
have distributions that are separated 
along environmental gradients such 
as depth, the inability to distinguish 
the two species would have negatively 
affected the model fits. This may have 
accounted for some of the variability 
not explained by the habitat model. 
The variability around the points 
in the annual abundance indices 
was similar for the stratified bottom 
trawl survey estimate and the habitat 
models. However, the habitat model- 
based estimates of variability around 
the CPUE estimates were generally 
slightly smaller on average and con- 
sistent from year to year. The Pacific 
ocean perch CPUE time series from 
the stratified survey estimate showed 
inconsistent variability patterns, with 
narrow confidence bands in years of 
low abundance and wider confidence 
intervals in years of higher abun- 
dance. The habitat model-based esti- 
mates did not show this kind of varia- 
tion and were much more consistent 
across years. The average CV for the 
