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Fishery Bulletin 1 10(3) 
densities in both the depth layer above and in the dead 
zone, along with a flat seafloor over the beam width. 
Yet, as documented in this study, densities can vary 
within very small distances from the seafloor, and un- 
trawlable areas are, by definition, not flat. 
The other method used for estimating abundance in 
the dead zone relies more on the relative abundance of 
each species in the dead zone compared to that in the 
zone above the area where backscatter can reliably be 
measured. The backscatter was then extrapolated to 
the dead zone by using the estimated ratio of species 
relative abundance. This method is much more reliant 
on estimation of ratios of species relative abundance 
and the depth layer used in ratios. In our present ex- 
ample, no estimate could be made for harlequin rock- 
fish when the 1.0-m depth layer was used because this 
species was not present above 1.0 m for extrapolating 
data down for the dead zone. However, an estimate for 
harlequin rockfish was possible when the 0.5-m depth 
layer was used because this species was present in both 
the depth layers of 0-0.5 m and 0. 5-1.0 m. 
Abundance estimates calculated in our study rely 
heavily on video estimates of relative species counts 
and height off bottom. For that reason, original project 
plans were to deploy the SDC, ROV, and trawl in the 
same location successively to obtain a more accurate 
comparison of their performance. More frequent deploy- 
ments also were planned, but additional sampling tool 
deployments and comparisons were not possible because 
of weather and logistical difficulties. 
Rockfishes were associated with carbonate pave- 
ments and encountered in the vicinity of bubble seeps 
(Fig. 7). It is not clear whether this apparent relation- 
ship is a result of the particular substrate type in 
the vicinity of the plumes or the bubble plumes them- 
selves. To help determine the importance of carbonate 
pavements as rockfish habitat, more observations are 
needed to characterize this association and describe 
the geographical distribution of this habitat type in 
the GOA. 
Conclusions 
We examined the complexity of methods for obtain- 
ing accurate abundance estimates for species that are 
bottom-oriented and have an affinity for complex habitat. 
This study shows that an adequate survey of dominant 
species in untrawlable terrain can be performed with 
acoustic instruments in conjunction with an SDC-based 
sampling system. Expanding such a survey to a geo- 
graphic area larger than the one used in our study would 
be reasonable once suitable descriptors for substrate 
habitat classification are employed to characterize an 
area and enable untrawlable locations to be specifically 
targeted. Because of the patchy nature of the school- 
ing behavior of fishes and their attraction to specific 
topographical features, additional targeted camera effort 
would improve allocation of species distribution and 
counts. Combined biomass estimates from the trawlable 
and untrawlable areas would then provide a picture of 
species abundances that is much more representative 
over the entire management area than current practice 
estimates in which only data from trawlable areas are 
used. 
Acknowledgments 
The authors would like to thank the captains and crews 
of the NOAA Ship Oscar Dyson and the FV Epic Explorer. 
We also thank M. Martin, M. Wilkins, M. Zimmermann, 
and D. Demer for their work on the project. The manu- 
script was improved by reviews from P. Ressler and D. 
Somerton and three anonymous reviewers. This project 
was funded jointly by the North Pacific Research Board 
(NPRB publication no. 349) and the Alaska Fisheries 
Science Center. 
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