338 
Fishery Bulletin 1 10(3) 
Northern rockfish made up 20% of all fishes encoun- <0.5 m off 
tered at heights >0.5 m off the bottom with the SDC of northern 
but were a small percentage (3%) of all fishes observed the bottom 
100% 
90% 
80% 
70% j 
t 
I 60 % j; 
c 
o 50% 
(D 
CD 
| 40% 
<D 
O 
S 30% 
f 
20% ]; 
10% t 
0% 
■ ■ 
□ Other species 
D Unidentified rockfishes 
□ Unidentified juv. rockfishes 
H Other rockfishes 
Q Juv. Pacific ocean perch 
□ Harlequin rockfish 
^ Northern rockfish 
■ Dusky rockfish 
.NT 
4? 
% 
$ 
L> 
Figure 4 
Relative species composition observed by depth layer for each type of 
sampling tool: stereo-video drop camera (SDC), remotely operated vehicle 
(ROV), and bottom trawl. Note that the depth layers for each tool are of 
different heights off the bottom and that there are 3 layers for the ROV, 
2 for the SDC, and one for the trawl. 
1. 5-2.0 HI 
E 1.0-1 .5 
0.5-1 .0 
■ Dusky rockfish 
□ Northern rockfish 
□ Harlequin rockfish 
0-0.5 
0% 20% 40% 60% 80% 
Percentage of species encountered 
1 00% 
Figure 5 
Percentage of each major rockfish species — dusky ( Sebastes uariabi- 
lis), northern (S. polyspinis ), and harlequin rockfish {S. variegatus ) — 
encountered with the stereo-video drop camera by half-meter bins 
of height off the bottom. Note that harlequin rockfish were absent 
1-2 m off the bottom. 
the bottom (Fig. 4). However, the majority 
rockfish (39%) were encountered <0.5 m off 
(Fig. 5). 
Harlequin rockfish composed 21% of 
the fishes observed at heights <0.5 m 
off the bottom with the SDC (Fig. 4). 
Harlequin rockfish were observed only 
<1.0 m off the bottom with the SDC 
and were most prevalent (86%) <0.5 m 
off the bottom (Fig. 5). 
Remotely operated vehicle 
The ROV was deployed at 5 sites during 
the survey (Fig. 1). Of the dusky rock- 
fish observed with the ROV, -3% were 
found on the bottom and 11% were seen 
>2.0 m off the bottom. In contrast, 
-65% of harlequin rockfish and -50% 
of the northern rockfish observed with 
the ROV were on the bottom. 
Bottom trawl 
Trawl deployments were conducted at 
6 locations (Fig. 1). More than 98% of 
the individuals caught in the bottom 
trawl were from the 3 major rockfish 
species (dusky, northern, and harlequin 
rockfishes). 
Trawlability and abundance estimates 
The trawlability index derived from 
the multibeam sonar (Weber 1 ) sug- 
gested that the majority (73%) of the 
core area covered in our survey con- 
sisted of untrawlable habitat. Addi- 
tionally, the majority of the rockfish 
backscatter (95%) from the core area 
was located in that untrawlable habi- 
tat (Fig. 1). 
Only dusky rockfish were found >2.0 m 
off the bottom on the bank; therefore 
all rockfish backscatter >2.0 m off the 
bottom was attributed to that spe- 
cies. The resulting biomass estimate 
for dusky rockfish observed within the 
core area >2.0 m off the bottom was 
262 metric tons (t). 
Both dusky and northern rockfishes 
were observed 1. 0-2.0 m off the bot- 
tom; therefore, backscatter in that 
depth layer was split between these 
species based on their relative abun- 
dance in SDC counts (56% and 33%, 
respectively). The resulting biomass 
was 331 t for dusky rockfish and 103 t 
northern rockfish in the depth layer of 
1. 0-2.0 m off the bottom. 
