Rooper et al : Estimating species and size composition of rockfishes to verify targets in acoustic surveys 
319 
ods (Jones et al., 2012 [this issue] for details of the 
acoustic assessment). 
Remotely operated vehicle 
Target verification was conducted with a Phantom 
DS4 ROV (Deep Ocean Engineering, Inc., San Jose, 
CA) nicknamed “ Sebastes ” that is owned and oper- 
ated by the NOAA Southwest Fisheries Science 
Center (further details on this ROV and its capabili- 
ties can be found at http://swfsc.noaa.gov/textblock. 
aspx?Division=FRD&id = 8784, accessed February 2012). 
Video footage from the ROV was recorded with a for- 
ward-looking color camera (Sony FCB-IX47C module 
with 468x720 lines of horizontal resolution and 18x 
optical zoom, Sony Corp., Tokyo, Japan). High-resolution 
still images were also collected with a Scorpio digital 
camera (Nikon Coolpix 995 with 4x zoom, Nikon Corp., 
Tokyo, Japan) to aid in species identifications. Speed of 
the ROV was measured by a downward facing Explorer 
Doppler velocity logger (DVL, Teledyne RD Instruments, 
San Diego, CA) which was also used to calculate transect 
length. This DVL was calibrated over a known distance 
and was accurate to ±0.07% (J. Butler, unpubl. data). 
The average speed of the ROV during deployments was 
1.32 km/h (standard error [SE] = 0.65) and the average 
altitude was 2.31 m (SE = 0.75), although a constant 
speed, altitude, and heading was generally not main- 
tained during deployment. 
We used Canadian grid projections (Wakefield and 
Genin, 1987) calculated with 3-Beam software (Green 
Sky Imaging, Vero Beach, FL) to estimate the field of 
view for the ROV. This system uses 3 lasers on the 
ROV, the altitude of the vehicle and the pitch of the 
camera to calculate the field of view (Pinkard et al., 
2005). The 3 high-intensity lasers were mounted paral- 
lel to the horizontal axis of the video camera: 2 parallel 
red lasers on either side of the video camera spaced 20 
cm apart and 1 green laser that crosses the left parallel 
laser at 0.99 m and the right parallel laser at 2.72 m 
from the camera lens. The position of the green laser 
to the red lasers was used to calculate the distance 
from the camera lens to the seabed (i.e., slant range), 
and the parallel lasers provided a reference distance 
used to determine the field of view and fish length. For 
3 of 4 transects with relatively flat seafloor, the field of 
view was calculated every 2 seconds. The average field 
of view, 2.61 m (SE = 0.20), was used as an estimate of 
the search area for the remaining transect. 
The ROV was deployed from the starboard side of 
the Oscar Dyson when weather permitted (Beaufort 
sea state <6) and was equipped with an acoustic tran- 
sponder that provided its location relative to the ship. 
The position of the ROV on the sea floor was corrected 
in real-time by using WinFrog survey software (Fugro 
Pelagos, Inc., San Diego, CA). All other navigational 
data (e.g., water depth, temperature, heading, course 
over ground, etc.) were collected at 1-2 s intervals, 
synchronized, and logged by using WinFrog. The ROV 
tether was attached with a swivel to a clump weight, 
which was connected by a cable to a winch onboard 
the vessel. The ROV and clump weight were lowered 
in unison to -10 m above the seafloor at which point 
the cable to the clump weight was secured, monitored, 
and adjusted to maintain a clump-weight-elevation of 
>10 in (to avoid hitting the seafloor), while the ROV 
more closely approached the seafloor for identification 
of rockfishes and substrate type. 
General locations for investigation were provided to 
the bridge from scientists operating the fisheries acous- 
tics equipment and the ship’s position was adjusted to 
drift or slowly navigate over a site where fish targets 
had been identified. However, the ROV did not transit 
specific transects and instead the seafloor was searched 
in one general direction, sometimes diverting from a 
straight-line to allow identification of rockfish targets or 
explore boulder patches more closely: this approach re- 
sulted in variable headings, speeds, and areas searched 
within a single deployment. For this reason, densities 
of rockfish were not computed from these transects. 
However, we did calculate the area swept by the ROV 
(distance traveled multiplied by the field of view) for 
comparison with the other gear types. 
Bottom trawl 
The bottom trawl used was a modified version of the 
Poly Nor’Eastern bottom trawl currently used by the 
Alaska Fisheries Science Center (AFSC) for bottom 
trawl surveys of the Gulf of Alaska and the Aleutian 
Islands (Britt and Martin, 2001; Stauffer, 2004). The 
net modifications included replacement of the standard 
footrope with rockhopper gear, the addition of heavier 
bridles (1.9 cm), and double meshes in the belly of the 
net. The center section of the rockhopper gear consisted 
of 61 cm rockhopper discs spaced approximately 46 cm 
apart. The rockhopper discs were spaced at about 61 
cm on the wings and gradually tapered from 61 to 46 
cm diameter on the wing extensions. All rockhopper 
discs were separated by solid sections of 2- cm (10-in.) 
discs. The bottom trawl was fished with 5-m 2 Fishbuster 
trawl doors each weighing 1089 kg (NET Systems Inc., 
Bainbridge Island, WA). The bottom trawl modifications 
were designed to improve the ruggedness of the net and 
allow the net to sample seafloor considered untrawlable 
with the standard survey net. The net width and height 
of the bottom trawl were -17 m and 7 m respectively. 
The bottom trawl was towed at an average speed of 5.87 
km/h (3.17 knots) ranging from 5.24 to 6.32 km/h and 
was generally deployed against the prevailing current. 
The area swept by the bottom trawl was estimated as 
the distance fished multiplied by the net width. 
Stereo drop camera 
The stereo drop camera system and deployment winch 
are described in Williams et al., (2010). The system 
consisted of two parallel-mounted cameras that col- 
lected simultaneous underwater video at a resolution 
