Stereo-video better for reef fish surveys
The use of stereo-video surveys to monitor reef fish communities can vastly reduce the errors that plague more traditional survey techniques.
Monitoring of reef fish communities, particularly those in marine protected areas, is hampered by the high errors associated with diver based visual census. Using this technique, the effectiveness of monitoring programmes to detect change relies entirely on the skill of the individual observer in identifying species, counting individuals, and estimating length of fish and the boundaries of the survey area. For monitoring programmes the same single observer is unlikely to be used from year to year which further compounds the error as differences in species identification and length/dimension estimates between observers is difficult to standardise and control for.
Individual fish can be measured to within less than 5% error of their true length
Stereo-video eliminating errors
Stereo-video eliminates these errors and solves the concern of managing differences between observers.
Firstly, when using cameras in stereo, individual fish can be measured to within less than 5% error of their true length.
Secondly, complementary to obtaining the length measurement, the position of the individual fish relative to the centre of the cameras is obtained, thus the boundaries of the agreed survey area can be adhered to (and any individuals outside this boundary would not impact the data).
Thirdly, the problem of species misidentification (particularly prevalent in novice observers) is eliminated as identification sources can be consulted, therefore allowing novice observers to identify all species that are recorded on the video.
These benefits allow managers to use volunteers and novice observers to collect the required data without compromising data quality.
Stereo-video in Mozambique
In southern Mozambique, stereo-video has been used for two years to build baseline data for reef fish communities around Ponta Malongane. Here, volunteers have built baseline data from over 15,000 observations of individual fish to include over 180 species across 35 reef fish families. The same sites were surveyed in 2009 and 2010, and will be surveyed again in 2011, across depths from 10m to 24m.
Monitoring with Operation Wallacea
The technique will also be used as part of Operation Wallacea monitoring programmes in Indonesia, Honduras, and Cuba in 2011. These surveys in time will provide invaluable data for comparisons of the trajectory of reef fish communities in terms of diversity, abundance and length metrics across oceanic basins.