A comparison of underwater visual distance estimates made by scuba divers and a stereo-video system: implications for underwater visual census of reef fish abundance

By Euan Harvey, David J. Fletcher, Mark Shortis, Gary A. Kendrick. 2004

212 citations recorded by the source corpus.

Underwater visual census of reef fish by scuba divers is a widely used and useful technique for assessing the composition and abundance of reef fish assemblages, but suffers from several biases and errors. We compare the accuracy of underwater visual estimates of distance made by novice and experienced scientific divers and an under- water stereo-video system. We demonstrate the potential implications that distance errors may have on underwater visual census assessments of reef fish abundance. We also investigate how the accuracy and precision of scuba diver length estimates of fish is affected as distance increases. Distance was underestimated by both experienced (mean relative error =− 11.7%, s.d. = 21.4%) and novice scientific divers (mean relative error =− 5.0%, s.d. = 17.9%). For experienced scientific divers this error may potentially result in an 82% underestimate or 194% overestimate of the actual area censused, which will affect estimates of fish density. The stereo-video system also underestimated distance but to a much lesser degree (mean relative error =− 0.9%, s.d. = 2.6%) and with less variability than the divers. There was no correlation between the relative error of length estimates and the distance of the fish away from the observer.

Subfields: Ecology, Global and Planetary Change, Nature and Landscape Conservation

View Paper: https://www.semanticscholar.org/paper/58a0616d43b2837999c5d9769a164edc1c2929c1

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In Ecology

In Global and Planetary Change

In Nature and Landscape Conservation

Citations in the corpus

A comparison of temperate reef fish assemblages recorded by three underwater stereo-video techniques (2005, methodology): “ Harvey et al. 2004 ) and may be either baited or unbaited.”
Cost-efficient sampling of fish assemblages: comparison of baited video stations and diver video transects (2010, methodology): “…census methods have been identified, including fish behaviour (Cole 1994, Watson & Harvey 2007), inter-observer variability in species identification (Lincoln Smith 1988, Legg & Nagy 2006) and estimates of abundance (Sale & Sharp 1983, Lincoln Smith 1988) and length and range (Harvey et al. 2004).”
Behaviour of temperate and sub-tropical reef fishes towards a stationary SCUBA diver (2007, background): “Harvey et al. (2004) demonstrated that experienced scientific divers could possibly underestimate by 82% or overestimate by up to 194% the actual area censused through errors in their abilities to assess distance, which would influence estimates of fish abundance.”
A comparison of two survey methods: differences between underwater visual census and baited remote underwater video (2010, unknown): “One of the identified sources of bias using UVC is the difficulty that divers may have in accurately counting individuals (Harvey et al. 2004), which could be especially true if a species forms dense schools.”
Factors affecting the detection distances of reef fish: implications for visual counts (2011, background): “Recent advances in video-based techniques (e.g., Willis et al. 2000; Harvey et al. 2004; Watson et al. 2005) may improve the assessment of large and mobile species by minimizing the biases introduced by the presence of observers.”
The application of predicted habitat models to investigate the spatial ecology of demersal fish assemblages (2010, background): “Additionally, there is the added advantage of being able to measure the area sampled by the cameras ( Harvey et al. 2004 ).”
Underwater video techniques for observing coastal marine biodiversity: A review of sixty years of publications (1952–2012) (2014, background): “Stereo-275 video has been shown to provide more accurate estimates of both fish length and distance 276 than visual estimation by divers (Harvey et al., 2001a, 2001b, 2002a, 2004) or single video 277 14 (Harvey et al., 2002b).”
Bait attraction affects the performance of remote underwater video stations in assessment of demersal fish community structure (2007, background): “The key challenge is ensuring that the areas or volumes within which fish are counted are defined and consistent, requiring the use of stereovideo techniques (Harvey et al. 2004).”
A review of techniques for the identification and measurement of fish in underwater stereo-video image sequences (2013, background): “Keywords: underwater stereo-video, stock assessment, fisheries management, automated measurement, video sequences, multi-scene matching, surface reconstruction, deformable templates”
Assessing reef fish assemblage structure: how do different stereo-video techniques compare? (2010, methodology): “The transect width (5 m) was deWned during postprocessing of the stereo-imagery by determining the three-dimensional coordinates (x, y and z) of a Wsh and deciding whether it was inside or outside the transect (see Harvey et al. 2002, 2004 ).”
A comparison of visual‐ and stereo‐video based fish community assessment methods in tropical and temperate marine waters of Western Australia (2013, methodology): “Divers are, however, more likely to include fish in surveys that were observed outside the transect (Harvey et al. 2004), which may have contributed to higher estimates of target species when using UVC.”