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Fishery Bulletin 1 10(3) 
or untrawlable) were observed for dusky rockfish. Be- 
cause of the confounding of gear types for northern 
rockfish (all the small northern rockfish were measured 
by using the ROV in untrawlable areas and only one 
northern rockfish was measured in an untrawlable area 
with the SDC), these differences could not be tested for 
statistical significance. 
The percentages rockfish observed on a transect 
that could be measured varied between the ROV and 
SDC, although this difference was not statistically sig- 
nificant when a <-test was applied (P=0.056, <=-2.3, 
df=7). For the ROV an average of 9.9% (SE = 0.054) of 
the dusky rockfish, northern rockfish, harlequin rock- 
fish, and Pacific ocean perch observed on a transect 
could be measured. On average 41.9% (SE = 0.184) of 
these species captured in a trawl haul were measured, 
higher than the percentage with the optic methods 
(Fig. 5). With the SDC, 35.6% (SE = 0.100) of the rock- 
fish species observed on a transect could be measured 
(Fig. 5). 
Vertical distribution of fish and comparisons 
between trawlable and untrawlable areas 
The results of the acoustic survey indicated that 
the majority of rockfish were near the seafloor 
because the mean height off bottom of rockfish 
from all 8 acoustic survey passes was 1.5 m 
(Jones et al., 2012 [this issue]). Mean height 
off bottom during each of the 8 survey passes 
ranged from 1 to 3.25 m, a range that allowed 
most of the rockfish biomass to be observed with 
the ROV or SDC or captured in the trawl. The 
observed height off the seafloor, as measured 
with the SDC, varied significantly among rock- 
fish species from a random distribution accord- 
ing to a chi-squared test (Table 2). Harlequin 
rockfish, Pacific ocean perch, rosethorn rockfish 
(S. heluomaculatus), dark rockfish (S. ciliatus), 
and yelloweye rockfish {S. ruberrimus) were 
observed exclusively within 1 m of the seafloor 
(Fig. 6). The rockfish species found in the water 
column (>1 m off the seafloor) were dusky and 
northern rockfish, although these species were 
also found within the acoustic dead zone as 
well. The bottom trawl integrated rockfish catch 
from approximately 0 m to 7 m (the height of 
the net opening) off the seafloor and the ROV 
laser system does not allow for measurement of 
distance off the seafloor on a fine scale; there- 
fore the depth distributions of various rockfish 
species could not be precisely determined with 
these gear types. 
With a chi-squared test, we also detected a 
significant nonrandom distribution of rockfish 
species by habitat type; either trawlable or un- 
trawlable (Table 3). The proportion of fish in 
untrawlable areas was higher than in trawlable 
areas for the individual fish species (Fig. 7), as 
well as for the combined other rockfish group 
(yelloweye rockfish, redstripe rockfish ( S . pro- 
riger), redbanded rockfish (S. babcocki), dark 
rockfish, tiger rockfish, and rosethorn rockfish). 
P-tests indicated some of these differences were 
insignificant, because the proportion of dusky 
rockfish (P=0.10, <=-1.83, n = 10), northern rock- 
fish (P=0.33, <=-1.07, n = 6), and Pacific ocean 
perch (P=0.07, <=-2.12, n = 8) was not signifi- 
cantly higher in untrawlable areas than in traw- 
lable areas. All the harlequin rockfish and the 
Fork length (cm) 
Figure 2 
Length-frequency data for each gear type (ROV=remotely oper- 
ated vehicle, Trawl= bottom trawl=Trawl, and SDC = stereo drop 
camera) for dominant rockfish species observed at the Snakehead 
Bank, Alaska, in 2009. n = the number of fish measured for each 
species and gear type. 
