Stereo Video

Dr Caine Delacy, our head of science and technology for the expedition, used stereo-video to determine fish density, biomass, diversity and community structure along 1 500 km of the Western Australian coastline. The EAMT team will introduce this technology to the East African coastline, as we sample the coral reef ecosystem from Mozambique to Kenya.

Assessments of reef fish communities have historically been assessed mostly through fishing surveys, which cannot be used in sensitive areas, such as marine protected areas, or through the use of underwater visual census using SCUBA. However, visual census is hampered by the high errors associated with diver subjectivity and between-diver variability. Using this technique, the accuracy and precision of data collection rely entirely on the skill of the individual observer in identifying species, counting individuals and estimating the lengths of fish and the boundaries of the survey area. The use of stereo-video surveys to monitor reef fish communities can vastly reduce the errors that plague more traditional survey techniques.

Stereo-video benefits

Firstly, when using cameras in stereo, individual fish length can be measured to within 95% accuracy. 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 do not impact on the data). Thirdly, the problem of species misidentification (particularly prevalent in novice observers) is eliminated, as the video footage is stored and can be analysed in the laboratory, where reference materials can be consulted.

Why?

Biological assessments aimed at detecting temporal change require baseline data on abundance, diversity and fish size structure, against which more recent data can be compared, to show trends. However, to date there has been no collection of baseline data spanning the length of the east African coral reef ecosystem, using a standardised methodology.

In fact, data sets spanning such large expanses of reef ecosystem are rare in marine science and conservation.

· The data collected during the EAMT will thus be an invaluable resource, representing the first such baseline, using a standardised technology and sampling design throughout, against which future data can be compared.

· These data will allow us to comprehensively assess the status of the coral reef fish resources along Africa’s east coast, as well as the human impacts thereon.

· The resultant database will also provide a means to assess the performances and design of marine protected areas in the region, will be available for biogeographic studies, and will provide local and national governments with a tool for conservation planning at local and national scales.

· Data regarding the health of the fishes and the corals can also help us to understand the influence of climate change in this region