326 
Fishery Bulletin 1 10(3) 
Figure 5 
Average proportion (and standard error) of rockfish that were mea- 
sured out of the total number of dusky rockfish (Sebastes variabihs), 
northern rockfish (S. polyspinis), harlequin rockfish (S. uariegatus), 
and Pacific ocean perch (S. alutus) observed. Proportions were 
calculated for the 4 species from each transect surveyed with the 
remotely operated vehicle (ROV; n = 4 deployments), bottom trawl 
haul (trawl; n = 6 deployments) and stereo drop camera transect 
(SDC, n = 5 deployments) conducted at the Snakehead Bank, Alaska, 
in 2009 where length data were collected. The average proportions 
were computed by using transects as replicates. 
Table 2 
Chi-squared test for random distribution of each rockfish species at <1 m height off the seafloor. The observed frequency and 
expected frequency of each rockfish species <1 m off the seafloor are shown for data from stereo drop camera deployments where 
both cameras were functional and rockfish were observed during the deployment (n = 5 deployments). 
Species 
Observed frequency 
<1 m off bottom Species 
Expected frequency 
<1 m off bottom 
Dusky rockfish ( Sebastes variabilis ) 
7 
11 
Northern rockfish ( Sebastes polyspinis ) 
3 
11 
Harlequin rockfish (Sebastes uariegatus) 
7 
4 
Other rockfish: Pacific ocean perch ( Sebastes alutus), 
rosethorn (S. helvomaculatus), yelloweye (S. ruberrimus), 
and dark rockfishes (S. ciliatus) 
18 
9 
Total number of fish observed/^ 2 
68 
19 
X 2 (critical value, P=0.05, df=4) 
9.49 
in rockfish species composition on the seafloor in 
trawlable and untrawlable areas were observed during 
this study. Other studies of untrawlable habitats have 
revealed similar differences in rockfish species compo- 
sition near the seafloor when compared with trawlable 
areas (Matthews and Richards, 1991; Matthews, 1989; 
Rooper et al., 2007). Our observations highlight the 
potential that a considerable proportion of the rock- 
fish biomass (in this case harlequin, northern, and 
dusky rockfish) will be unavailable to the standard 
bottom trawl survey in untrawlable areas, potentially 
negatively biasing population abundance estimates. 
Although at least some of these species may be avail- 
able for acoustic biomass estimation, the abundance 
of species that are found in the acoustic dead zone in 
untrawlable areas will be more difficult to estimate 
