Hanselman et at: Application of an acoustic-trawl survey design to improve estimates of rockfish biomass 
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Stations sampled during an experimental rockfish acoustic-trawl survey conducted 
in 2009 near Yakutat, Alaska, at depths of 200-500 m. Gray triangles indicate “back- 
ground” stations, which were areas of low-density catch per unit of effort (CPUE) 
identified in the field through the use of acoustic data. Black circles indicate “patch” 
stations, which were areas of high CPUE identified in the field. 
our study area to the NMFS-delineated strata on the 
continental shelf break at depths of 200-500 in in the 
Yakutat area of the GOA (Fig. 2) because these depths 
contain the bulk of POP biomass. The sampling area 
was 7800 km 2 . 
The vessel used for our 2009 study was the FV Sea 
Storm, a 38-m stern ramp trawler with 1710 continuous 
horsepower. Stations were sampled with a standardized 
Poly-Nor’eastern high-opening bottom trawl rigged with 
roller gear and a 27.2-m headrope. All gear was the 
standard gear used for the NMFS GOA trawl surveys. 
For further details on the vessel and gear used for our 
2009 study, see the report by von Szalay et al. (2010). 
Acoustic backscatter was measured continuously during 
the day and during trawling, with a calibrated Sim- 
rad 2 (Kongsberg Maritime AS, Horten, Norway) ES60 
echosounder and a hull-mounted 38-kHz transducer. 
A total of 48 stations were preselected randomly from 
among stations that were successfully trawled during 
previous NMFS GOA trawl surveys (Fig. 2). The use of 
previously trawled locations eliminated search time for 
new locations suitable for random trawls. Once random 
stations were selected, we constructed the most efficient 
2 Mention of trade names or commercial companies is for 
identification purposes only and does not imply endorsement 
by the National Marine Fisheries Service, NOAA. 
path, or trackline, to connect these planned stations. 
Depending on the acoustic backscatter encountered 
during a survey, these planned stations were later clas- 
sified as either “background stations” (with low CPUE) 
or “patch stations” (with high CPUE). 
The identification of patch stations required a simple 
and consistent definition for the spatial variability in 
acoustic backscatter along the trackline so that we 
could determine areas of intense backscatter that were 
large enough for bottom trawling. Acoustic backscatter 
data were examined in real time by using the Echo- 
view live viewing module (Myriax Pty., Ltd., Hobart, 
Australia), and Echoview scripts were used to integrate 
the acoustic backscatter in cells along the seafloor. The 
conformal cells in this analysis had a height of 10 m 
(from 1.5 m to 11.5 m off the seafloor) and a length of 
100 m. The lower boundary of each cell was situated 1.5 
ni off the seafloor to avoid errors in Echoview-derived 
bottom detection and to account for the “acoustic dead 
zone” (Simmonds and MacLennan, 2005) — the area 
where fishes are difficult to detect acoustically because 
the echo from the seafloor masks their acoustic signals. 
The value of 1.5 m was estimated with the equations 
in Ona and Mitson (1996) and a peak POP depth of 
-225 m (Hanselman et al., 2001). The 10-m height of 
the cells examined in our study was considerably larger 
than the mean height (-6 m) of the nets used in NMFS 
