Action cameras can measure fish accurately
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PELAGIC STEREO-BRUVS
A fleet of pelagic baited remote underwater video systems (BRUVS) ready for deployment. Each unit is fitted with GoPro cameras mounted at two different angles. By combining both video clips, researchers can estimate the size (body length) of wildlife species with a high level of accuracy.
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ALL ABOUT LENGTH
Kernel density estimates for fish community length-frequency distribution using the two different camera systems. The shaded area represents one standard error in either side of the null model of no difference between the KDEs for each camera system.
CITATION
Letessier TB, Juhel JB, Vigliola L, Meeuwig JJ. 2015. Low cost GoPro cameras generates accurate underwater stereo measurements of fish. Journal of Experimental Marine Biology and Ecology, 466: 120-126.
HIGHLIGHTS
Small action cameras arranged in a stereo configuration generated accurate measurements of fish body lengths at less than 5 m distance and 25° angle.
Action cameras were slightly less accurate than handheld cameras in an enclosed pool environment but no difference was observed in situ.
Small action cameras provide cheap and sufficiently accurate measurements of fish when compared to handheld cameras.
ABSTRACT
Small action cameras have received interest for use in underwater videography because of their low-cost, standardised housing, widespread availability and small size. Here, we assess the capacity of GoPro action cameras to provide accurate stereo-measurements of fish in comparison to the Sony handheld cameras that have traditionally been used for this purpose. Standardised stereo-GoPro and Sony systems were employed to capture measurements of known-length targets in a pool to explore the influence of the type of camera, distance to camera rig, angle to the optical axis and target speed on measurement accuracy.
The capacity to estimate fish length in situ was also compared by measuring the same fish on a coral reef with two baited remote underwater video systems, each fitted with both a GoPro and a Sony camera system. Pool trials indicated that the GoPros were generally less accurate than the Sonys. Accuracy decreased with increased angles and distance for both systems but remained reasonably low (< 7.5%) at 5 m distance and 25° angle for GoPros. Speed of target movement did not result in any consistent decrease in accuracy. In situ measurements revealed a strong correlation (R2 = 0.94) between Sony and GoPro length measurements of the same individual fish, with a slope not different from 1 and an intercept not different from 0, suggesting that GoPro measurement errors do not result in a consistent bias at the level of individual fish. Moreover, the investigation of kernel density functions of the length distribution of the entire fish assemblage indicated that difference in measurement accuracy becomes negligible for purposes of comparing population size structure. We suggest a measurement protocol for the use of GoPro stereo-camera systems that improves accuracy, where distance to target is limited to 5 m and angle to optical axis is restricted to 25°. For distances up to 7 m, angles should be restricted to 15°. This protocol supports the use of small action cameras such as the GoPro system, providing reductions in cost and increases in effective sampling efforts, compared with traditional rigs based on relatively expensive handheld cameras.
FUNDING & ACKNOWLEDGEMENTS
We are grateful for guidance and support provided by David Mouillot and Laurent Wantiez. We thank the Government of New Caledonia and the crew of the Amborella for excellent seamanship and support during our camera deployment activities. For technical support during pool experiments, we thank Mr Lloyd Groves and Mr Robert Sanzogni. TBL was supported by the Marine Biodiversity Hub through the Australian Government’s National Environmental Research Program (NERP). NERP Marine Biodiversity Hub partners include the Australian Institute of Marine Science, CSIRO, Charles Darwin University, Geoscience Australia, Museum Victoria, University of Tasmania and the University of Western Australia. Fieldwork in New Caledonia was supported by the PRISTINE program funded by the TOTAL Foundation.