Williams et al.: Use of stereo-camera systems in assessing rockfish abundance and pollock behavior 
353 
Table 1 
Design, manufacturer, and cost (approximate estimates in U.S. dollars) for drop stereo-video camera and still-frame stereo- 
camera systems used for surveying untrawlable habitat and studying fish behavior in midwater research trawls. Both sys- 
tems were used in the field in July 2008 and July 2007, respectively. HID=high-intensity discharge; LED=light-emitting diode; 
UHMW = ultra high molecular weight plastic. 
System 
Component 
Design 
Manufacturer 
Cost 
Drop stereo- 
HID light 
HID Xenon lights, 12 V, 50 W 
Underwater Lights USA 
$814 
video 
Video line driver 
Balanced line driver and transceiver 
Nitek 
$133 
camera 
Conducting cable 
4 conductor wire, 4.72 mm diameter 
Rochester Cable 
$1601 
Sled frame 
Aluminum channel and tubing 
Local manufacture 
$2000 
Winch and slip ring 
CSW-6 electronic win 
A.G.O. Environmental 
$11,268 
Underwater housings 
cameras 
5" diameter 
Local manufacture 
$729 
Underwater housings 
lights 
— 
Local manufacture 
$729 
LED sync 
— 
Ramsey Electronics 
$24 
Underwater cable and 
connections 
— 
Teledyne Impulse 
$614 
Batteries 
4x12 V 4 Ah NiMH 
Energy sales 
Total video system cost 
$396 
$18,308 
Still-frame 
Strobe 
Oceanic 3000 
Oceanic 
$990 
stereo 
Cameras 
Canon Digital Rebel Xt (8Mp) 
Canon USA 
$1100 
camera 
Lenses 
Canon EF 28 mm f/2.8 
Canon USA 
$450 
Microcontroller & 
circuitry 
— 
Local manufacture 
$150 
Underwater housings 
and viewports 
10" floats, 1.5" acrylic flat viewports 
Local manufacture 
$1400 
Mounting frame 
UHMW plastic and aluminium stock 
Local manufacture 
$350 
Underwater connections 
— 
Teledyne Impulse 
$650 
Batteries 
Software 
3x12 V 4 Ah NiMH 
Matlab V 7.6 
Energy sales 
Total still-frame system cost 
Mathworks 
$297 
$5387 
(i.e., van Rooij and Videler, 1996; Shortis et al., 2009). 
The recent development of high-resolution digital cam- 
eras has vastly improved the performance and reduced 
the complexity of image-based sampling because high- 
quality digital images can be directly analyzed with 
image-processing software. In general, stereo methods 
provide highly precise measurements in comparison to 
single-camera-based photogrammetric methods (Har- 
vey et al., 2002). However, these systems necessitate 
maintaining a stable two-camera geometry and must be 
initially calibrated with targets of known sizes. Despite 
these constraints, stereo photography is widely used in 
optical-based sampling in a variety of marine studies. 
We demonstrate the precision of stereo-camera-based 
measurements, attainable from initial deployments in 
the field, in comparison with traditional survey mea- 
surements. The results show that stereo-based optical 
sampling is a viable method for augmenting bottom- 
trawl data for abundance estimations; the stereo cam- 
eras allow scientists to survey sampling areas that are 
unavailable to standard survey trawl gear. In addition, 
stereo cameras can be used to observe and quantify 
the behavior of fish in the process of being captured by 
trawl gear to further improve estimates of abundance 
because they allow scientists to determine the potential 
biases in trawl-based catch data. 
Materials and methods 
Sampling untrawlable areas with the 
video-drop camera system 
The design of the video-drop system was based on two 
key needs. Because rockfish are found in areas of high 
relief, the camera needed to have adequate protection 
for their electronic components and have the ability to 
maintain visual contact with the bottom through rough 
substrate areas. Therefore, essential to sampling with 
this camera system was the ability to live-view the video 
and the use of a quick-responding winch system that 
could be controlled by the operator aboard the research 
vessel. The specifications of the camera components are 
presented in Table 1. 
The winch used to deploy and retrieve the camera 
system and navigate the seafloor was a CSW-6 multi- 
purpose win (A.G.O. Environmental, Nanaimo, BC, 
Canada; Fig. 1A). The winch motor was a 3 /4 horse- 
