Stereo Video

Stereo-video provides an accurate and efficient method for quantifying the abundance and size of reef fish and other underwater organisms. At CRRF we are using a variety of different applications of stereo-video to answer questions regarding fish ecology, fisheries and benthic habitat changes.

Quantifying fish abundance and size

Stereo-video systems are mainly used in two different applications for quantifying the abundance and size of fish. The diver-operated stereo-video system (stereo-DOV) is used by divers swimming transects so that fish counts can be done more quickly and the survey area can be standardised. The other common use is with a baited remote underwater video station (stereo-BRUV) which is deployed from a boat and can be used to survey deep waters and also useful for attracting predatory fish that can be shy of divers such as sharks.

Studying fish spawning aggregations

The ability to rapidly collect data on fish abundance and size makes the use of stereo-video a useful method for studying fish spawning aggregations. As only reproductively active fish participate in the aggregation, we are investigating if size of fish that are aggregating can provide an accurate indicator of the size of maturity.

Fish landing surveys

We use a compact stereo-video camera to film fish catches during unloading at the fish market and at other fish landing sites. The camera provides a fast way to record the species composition and size of fish with minimal disruption to the market and fishers. As there are 100’s of fish species landed, having images to identify fish to species level is very useful. The size of fish is needed for fishery stock assessments.

Benthic surveys of deep reefs

The use of video saves time when recording the benthic habitat and provides a permanent record of the condition of the reef. This is especially important on deep ‘mesophotic’ reefs where dive time is very limited. Using a stereo-video camera, we can also calculate of area of the image so quadrats are not needed. Footage can be used to create 3D models of reef complexity and surface area.

How it works

Stereo-video works though a process called photogrammetry, where the 3-D coordinates of points on an object can be determined from the known location of two cameras. After calibration and filming, measurements can be made using the computer program EventMeasure-stereo (www.seagis.com.au). It requires the user to click on the head and tail of each fish on the left and right images. It then calculates the length measurement and a species name can be chosen from drop-down menu. All measurements are recorded with other details and can be easily exported to make graphs on the abundance and size of fish.