328 
Fishery Bulletin 1 10(3) 
deployed in reasonably close proximity in space over the 
same time period. We observed uniformity of species 
composition within trawlable and untrawlable habitats 
when sampling with the two optical gear types. For 
example, dusky rockfish and northern rockfish were the 
dominant species observed with both optical gear types 
in trawlable areas, whereas additional rockfish species 
such as harlequin rockfish were found with the optical 
gear types (as well as the trawl) in untrawlable ar- 
eas. This result would not be expected if we were sam- 
pling substantially different communities in the 
small area the Snakehead Bank. The acoustic 
information showed that the biomass of fish in 
the Snakehead Bank area was relatively stable 
between eight successive day and night pass- 
es (-2800 t, coefficient of variation [CV] = 0.27; 
Jones et al., 2012 [this issue]), indicating it was 
unlikely that substantial fish movement into or 
out of the study area would have influenced the 
results. 
The spatial scale of the effort varied also with 
each gear type in this study. The bottom trawl 
covered a wide area, whereas the two optical 
technologies covered only small swaths of the 
seafloor. This difference in spatial scale probably 
affected the catchability of the gear types. The 
substrate type also affected the catchability. In 
the more rugose substrate, the ROV and SDC 
allowed rockfish to be observed in individual 
cracks and crevices although identifying indi- 
viduals partially hidden in crevices was more 
difficult with the SDC. The modified bottom 
trawl undoubtedly did not capture all the fish 
species that occurred in the most rugose areas. 
The modifications to the footrope were designed 
to allow the net to bounce over large rocks and 
probably led to some fish in rocky areas not be- 
ing captured. 
Fish length differed between the 3 gear types. 
The smallest fish were observed only with the 
■ Trawlable 
100% 
90% 
80% 
70% 
<u 
60% 
CTJ 
S 50% 
o 
<5 40% - 
CL 
30% - 
20% i 
10 % - 
0 % - 
Dusky rockfish Northern Harlequin Pacific ocean Other rockfish 
{S. variabilis) rockfish rockfish perch (5. spp.) 
(S. polyspmis ) (5. variegatus ) (5. alutus ) 
Figure 7 
Mean percentage (and standard errors) of rockfish by species 
observed in trawlable and untrawlable areas as estimated with 
the stereo drop camera and remotely operated vehicle along 
the transects. Only transects that included both trawlable and 
untrawlable areas and transects where the rockfish species 
occurred were used to calculate the mean percentages. The other 
rockfish species group includes yelloweye rockfish ( Sebastes 
ruberrimus), redstripe rockfish (S. proriger ), redbanded rock- 
fish (S. babcocki), dark rockfish (S. cihatus), tiger rockfish, 
(S. nigrocinctus), and rosethorn rockfish (S. helvomaculatus). 
Table 4 
Estimated total hours spent deploying each gear type to collect one bottom trawl sample from a 5-15 minute tow and one hour of 
underwater images from either the remotely operated vehicle (ROV) or the stereo drop camera (SDC). Each major data collection 
task (identifying, counting, and measuring all species of fish) and data entry is listed, as well as the relative level of expertise 
required to complete the task. Underwater video was used for substrate classification, fish counting, and identification for the 
ROV and SDC. Still images were used for determining fish length for the ROV and SDC, and still images were used to aid fish 
identification with the ROV. 
ROV Bottom trawl SDC 
Estimated Level of Estimated Level of Estimated Level of 
time required expertise time required expertise time expertise 
Task (person hours) required (person hours) required (person hours) required 
Deployment and retrieval of gear 
2.5 
High 
1 
High 
1.5 
High 
Classification of substrate 
0.5 
High 
— 
— 
0.5 
High 
Fish count and identification 
2 
High 
0.5 
Medium 
2 
High 
Determination of fish length 
3 
High 
0.5 
Low 
2 
High 
Data entry and formatting 
1 
Medium 
0.5 
Medium 
1 
Medium 
Total 
9 
2.5 
7 
Initial cost of equipment 
>$100,000 
$66,000 
$18,308 
Operational cost (per ha of seafloor) 
$1,393 
$139 
$262 
