Rooper et al.: Estimating species and size composition of rockfishes to verify targets in acoustic surveys 
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Table 1 
Number of deployments, rockfish species observed or caught, percentage of rockfish not identified to species, total area swept, and 
percentage of area that was untrawlable for each gear type: remotely operated vehicle (ROV), modified bottom trawl (trawl), and 
stereo drop camera (SDC). Trawlability was defined in reference to the standard Poly-Nor’Eastern 4-seam bottom trawl used by 
the Alaska Fisheries Science Center in biennial bottom trawl surveys of the Gulf of Alaska and Aleutian Islands (Stauffer, 2004 ), 
not the modified bottom trawl used during our study. 
ROV 
Trawl 
SDC 
Deployments 
4 
6 
8 
Rockfish observed 
Pacific ocean perch 
Sebastes alutus 
107 
9 
10 
Dusky rockfish 
S. variabilis 
700 
4733 
500 
Northern rockfish 
S. polyspmis 
31 
254 
148 
Dark rockfish 
S. ciliatus 
7 
40 
8 
Harlequin rockfish 
S. uariegatus 
166 
1942 
151 
Redbanded rockfish 
S. babcocki 
5 
Tiger rockfish 
S. nigrocinctus 
3 
Redstripe rockfish 
S. proriger 
80 
2 
Pygmy rockfish 
S. wilsoni 
1 
Silvergrey rockfish 
S. breuispinis 
4 
Rosethorn rockfish 
S. helvomaculatus 
3 
Yelloweye rockfish 
S. ruberrimus 
36 
8 
5 
Unidentified rockfish 
Sebastes spp. 
116 
351 
Total rockfish species 
9 
9 
7 
Total rockfish observed 
1251 
6993 
1176 
Percentage unidentified 
9.3% 
0.0% 
29.8% 
Total area swept (ha) 
2.70 
4.66 
2.62 
Percentage untrawlable 
46.0% 
100.0% 
74.6% 
similar (-2.7 and 2.6 ha) and the amount of seafloor 
swept by the bottom trawl was much greater (4.7 ha). 
There were significant differences in the percentages 
of fish identified to species with the 3 gear types by us- 
ing ANOVA (P=0.002, F=10.45, n = 16). The percentage 
of fish not identified to species was low for the ROV 
(9.3%), where control of the camera allowed individual 
fish to be followed and examined for species identifica- 
tion (Table 1). Fish identification was complete with the 
bottom trawl because all individuals could be closely 
examined and unambiguously identified. The high per- 
centage of unidentified rockfish (29.8%) with the SDC 
reflects our inability to finely control the position and 
attitude of the drop camera system to closely examine 
fish for identification. 
Measurement of fish length 
Length distributions of dusky rockfish and harlequin 
rockfish were not significantly different (P=0.71 and 
P=0.34) between the ROV and SDC (Fig. 2). The length 
distributions were significantly different between the 
bottom trawl and the two optical methods (ROV and 
SDC) for dusky rockfish (P=0.018 and P=0.013) and 
for harlequin rockfish (P=0.003 and P=0.002). Length 
distributions for Pacific ocean perch were significantly 
different (P=0.03) between the ROV and bottom trawl 
(there were not enough samples from the SDC to con- 
duct statistical tests). Length distributions of northern 
rockfish from each of the gear types were significantly 
different (PcO.Ol). 
Analysis of variance revealed that mean lengths of 
the major rockfish species collected in this study var- 
ied significantly among gear types (Fig. 3). Tukey’s 
post hoc tests for 3 species of rockfishes (dusky rock- 
fish, harlequin rockfish, and Pacific ocean perch) in- 
dicated there were no significant differences in mean 
length measured with the 2 optical gear types (P>0.05). 
Tukey’s post hoc tests indicated that the mean length 
of northern rockfish from the ROV was significantly 
shorter than those estimated by the SDC, and northern 
rockfish measured by both the optical methods were 
significantly shorter than those measured from the 
bottom trawl. Mean lengths of harlequin rockfish from 
the ROV and SDC were significantly shorter than those 
from the trawl. Dusky rockfish and Pacific ocean perch 
mean lengths were the same for all 3 methods. In gen- 
eral, more shorter fish were observed with the optical 
methods than with the bottom trawl. Interestingly, the 
mean length of northern rockfish from untrawlable ar- 
eas was shorter than that from trawlable areas (Fig. 4), 
although no differences in length by habitat (trawlable 
