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
Euan Harvey A D , David Fletcher B , Mark R. Shortis C and Gary A. Kendrick AA School of Plant Biology, Faculty of Natural and Agricultural Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
B Department of Mathematics and Statistics, University of Otago, PO Box 56, Dunedin, New Zealand.
C Science, Engineering and Technology Portfolio, RMIT University, GPO Box 2476V, Vic. 3001, Australia.
D Corresponding author. Email: euanh@cyllene.uwa.edu.au
Marine and Freshwater Research 55(6) 573-580 https://doi.org/10.1071/MF03130
Submitted: 28 August 2003 Accepted: 28 June 2004 Published: 14 September 2004
Abstract
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 underwater 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.
Extra keywords: accuracy, bias, precision, sampling error.
Acknowledgments
The authors acknowledge grants and financial aid from the New Zealand Department of Conservation (Research Grant #1822), the University of Otago Research Committee, the Southland Regional Council (New Zealand) and the Division of Sciences at the University of Otago, Dunedin, New Zealand that made this research possible. Also acknowledged is support from Sony New Zealand Ltd, THC Milford Sound, Fiordland Lobster Co. and Mobil and Gore Services Ltd. This work was completed thanks to postdoctoral fellowship funding from the New Zealand Foundation for Research Science and Technology and the University of Western Australia to Euan Harvey. The authors are grateful to Chris Battershill, June Hill, Justin McDonald, Philip Mladenov and Di Watson and for comments and suggestions on this manuscript. Additionally, our thanks to all novice and experienced scientific observers who willingly gave their time to assist with this research.
Andrew, N. L. , and Mapstone, B. D. (1987). Sampling and the description of spatial pattern in marine ecology. Oceanography and Marine Biology Annual Review 25, 39–90.
Bell, J. D. (1983). Effects of depth and marine reserve fishing restrictions on the structure of a rocky reef fish assemblage in the north-western Mediterranean Sea. Journal of Applied Ecology 20, 357–369.
Bell, J. D. , Craik, G. J. S. , Pollard, D. A. , and Russell, B. C. (1985). Estimating length frequency distributions of large reef fish underwater. Coral Reefs 4, 41–44.
Bohnsack, J. A. and Bannerot, S. P. (1986). ‘A Stationary Visual Census Technique for Quantitatively Assessing Community Structure of Coral Reef Fishes.’ Technical Report NMFS 41. (US Department of Commerce NOAA: La Jolla, CA, USA.)
Bohnsack, J. A. , Harper, D. E. , McClellan, D. B. , and Hulsbeck, M. (1994). Effects of reef size on colonisation and assemblage structure of fishes at artificial reefs off southeastern Florida, U.S.A. Bulletin of Marine Science 55, 796–823.
Bortone, S. A. , Kimmel, J. J. , and Bundrick, C. M. (1989). A comparison of three methods for visually assessing reef fish communities: Time and area compensated. Northeast Gulf Science 10, 85–96.
Brock, V. E. (1954). A preliminary report on a method of estimating reef fish populations. The Journal of Wildlife Management 18, 297–308.
Buckland, S. T., Anderson, D. R., Burnham, K. P., and Laake, J. L. (1993).
Caughley, G. (1977).
Caughley, G. R. , Sinclair, R. , and Scott-Kemmis, D. (1976). Experiments in aerial survey. The Journal of Wildlife Management 40, 290–300.
Choat, J. H. , and Bellwood, D. R. (1985). Interactions amongst herbivorous fishes on a coral reef: influence of spatial variation. Marine Biology 89, 221–234.
Cormack, R. M., Patil, G. P., and Robson, D. S. (1979).
Darwall, W. R. T. , and Dulvy, N. K. (1996). An evaluation of the suitability of non-specialist volunteer researchers for coral reef fish surveys. Mafia Island, Tanzania – A case study. Biological Conservation 78, 223.
| CrossRef |
Davis, G. E. , and Anderson, T. W. (1989). Population estimates of four kelp forest fishes and an evaluation of three in situ assessment techniques. Bulletin of Marine Science 44, 1138–1151.
Draper, N. R., and Smith, H. (1981).
English, S., Wilkinson, C., and Baker, V. (1994).
Estes, J. A. , and Gilbert, J. R. (1978). Evaluation of an aerial survey of Pacific Walruses (Odobenus rosmarus divergens). Journal of the Fisheries Research Board of Canada 35, 1130–1140.
Francis, C. M. (1994). Population changes of boreal forest ducks – A comment. The Journal of Wildlife Management 58, 582–586.
Francour, P. (1997). Fish assemblages of Posidonia oceanica beds at Port-Cros (France, NW Mediterranean): Assessment of composition and long-term fluctuations by visual census. Marine Ecology 18, 157–173.
GBRMPA, (Great Barrier Reef Marine Park and Authority) (1979).
Greene, L. E. , and Alevizon, W. E. (1989). Comparative accuracies of visual assessment methods for coral reef fishes. Bulletin of Marine Science 44, 899–912.
Harman, N. , Harvey, E. , and Kendrick, G. D. (2003). Differences in fish assemblages from different reef habitats in Hamelin Bay, southwestern Australia. Marine and Freshwater Research 54, 177–184.
| CrossRef |
Harvey, E. S. , and Shortis, M. R. (1996). A system for stereo-video measurement of subtidal organisms. Journal of the Marine Technology Society 29, 10–22.
Harvey, E. , and Shortis, M. R. (1998). Calibration stability of an underwater stereo-video system: Implications for measurement accuracy and precision. Marine Technology Society Journal 32, 3–17.
Harvey, E. S. , Fletcher, D. , and Shortis, M. R. (2001a). A comparison of the precision and accuracy of estimates of reef-fish lengths made by divers and a stereo-video system. Fishery Bulletin (Washington, D.C.) 99, 63–71.
Harvey, E. S. , Fletcher, D. , and Shortis, M. (2001b). Improving the statistical power of visual length estimates of reef fish: A comparison of estimates determined visually by divers with estimates produced by a stereo-video system. Fishery Bulletin (Washington, D.C.) 99, 72–80.
Harvey, E. S. , Fletcher, D. , and Shortis, M. R. (2002a). Estimation of reef fish length by divers and by stereo-video. A first comparison of the accuracy and precision in the field on living fish under operational conditions. Fisheries Research 57, 255–265.
| CrossRef |
Harvey, E. S. , Shortis, M. R. , Stadler, M. , and Cappo, M. (2002b). A comparison of the accuracy and precision of digital and analogue stereo-video systems. Marine Technology Society Journal 36, 38–49.
Jennings, S. , and Polunin, N. V. C. (1995). Biased underwater visual census biomass estimates for target-species in tropical reef fisheries. Journal of Fish Biology 47, 733–736.
| CrossRef |
Kingsford, M., and Battershill, C. (1998).
Lincoln-Smith, M. P. (1988). Effects of observer swimming speed on sample counts of temperate rocky reef fish assemblages. Marine Ecology Progress Series 43, 223–231.
Marsh, H. , and Sinclair, D. F. (1989). Correcting for visibility bias in strip transect aerial surveys of aquatic fauna. The Journal of Wildlife Management 53, 1017–1024.
McCormick, M. I. , and Choat, J. H. (1987). Estimating total abundance of a large temperate reef fish using visual strip-transects. Marine Biology 96, 469–478.
Odum, H. T. , and Odum, E. P. (1955). Trophic structure and productivity of a windward coral reef community on Eniwetok Atoll, Marshall Islands. Ecological Monographs 25, 291–320.
Polunin, N. V. C. , and Roberts, C. M. (1993). Greater biomass and value of target coral reef fishes in two small Caribbean marine reserves. Marine Ecology Progress Series 100, 167–176.
Rakitin, A. , and Kramer, D. L. (1996). Effect of a marine reserve on the distribution of coral reef fishes in Barbados. Marine Ecology Progress Series 131, 97–113.
Ralph, C. J., and Scott, J. M. (1981).
Russ, G. R. , and Alcala, A. C. (2003). Marine reserves: Rates and patterns of recovery and decline of large predatory fish, 1983–2000. Ecological Applications 13, 1553–1565.
Samoilys, M. A., and Carlos, G. (1992).
Shortis, M. R. , and Harvey, E. S. (1998). Design and calibration of an underwater stereo-video system for the monitoring of marine fauna populations. International Archives Photogrammetry and Remote Sensing 32, 792–799.
St. John, J. , Russ, G. R. , and Gladstone, W. (1990). Accuracy and bias of visual estimates of numbers, size structure and biomass of coral reef fish. Marine Ecology Progress Series 64, 253–262.
Thompson, A. A. , and Mapstone, B. D. (1997). Observer effects and training in underwater visual surveys of reef fishes. Marine Ecology Progress Series 154, 53–63.
Thresher, R. E. , and Gunn, J. S. (1986). Comparative analysis of visual census techniques for highly mobile, reef associated piscivores (Carangidae). Environmental Biology of Fishes 17, 93–116.
Watson, R. A. , Carlos, G. M. , and Samoilys, M. A. (1995). Bias introduced by the non-random movement of fish in visual transect surveys. Ecological Modelling 77, 205–214.
| CrossRef |
Westera, M. , Lavery, P. , and Hyndes, G. (2003). Differences in recreationally targeted fishes between protected and fished areas of a coral reef marine park. Journal of Experimental Marine Biology and Ecology 294, 145–168.
| CrossRef |