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

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.

[1]  Samoilys.  Review of the underwater visual census method developed by DPI-ACIAR project: visual assessment of reef fish stocks. [Workshop proceedings] , 1992 .

[2]  M. Kingsford,et al.  Studying temperate marine environments : a handbook for ecologists , 2000 .

[3]  M. McCormick,et al.  Estimating total abundance of a large temperate-reef fish using visual strip-transects , 1987 .

[4]  H. Odum,et al.  Trophic Structure and Productivity of a Windward Coral Reef Community on Eniwetok Atoll , 1955 .

[5]  N. Polunin,et al.  Greater biomass and value of target coral-reef fishes in two small Caribbean marine reserves. , 1993 .

[6]  Ganapati P. Patil,et al.  Sampling Biological Populations. , 1981 .

[7]  W. Darwall,et al.  An evaluation of the suitability of non-specialist volunteer researchers for coral reef fish surveys. Mafia Island, Tanzania — A case study , 1996 .

[8]  G. Davis,et al.  Population estimates of four kelp forest fishes and an evulation of three in situ assessment techniques , 1989 .

[9]  D. Kramer,et al.  Effect of a marine reserve on the distribution of coral reef fishes in Barbados , 1996 .

[10]  Euan S. Harvey,et al.  Design and Calibration of an Underwater Stereo-video System for the Monitoring of Marine Fauna Populations , 2001 .

[11]  G. Russ,et al.  MARINE RESERVES: RATES AND PATTERNS OF RECOVERY AND DECLINE OF PREDATORY FISH, 1983–2000 , 2003 .

[12]  Stephen A. Bortone,et al.  A Comparison of Three Methods for Visually Assessing Reef Fish Communities: Time and Area Compensated , 1989 .

[13]  Euan S. Harvey,et al.  Calibration stability of an underwater stereo-video system : Implications for measurement accuracy and precision , 1998 .

[14]  J. Estes,et al.  Evaluation of an Aerial Survey of Pacific Walruses (Odobenus rosmarus divergens) , 1978 .

[15]  G. Russ,et al.  Marine Reserves: Rates and Patterns of Recovery and Decline of Large Predatory Fish , 1996 .

[16]  Shortis,et al.  A System for Stereo-Video Measurement of Sub-Tidal Organisms: Implications for assessments of reef fish stocks , 1995 .

[17]  Euan S. Harvey,et al.  A comparison of the precision and accuracy of estimates of reef-fish lengths determined visually by divers with estimates produced by a stereo-video system. , 2001 .

[18]  R. Thresher,et al.  Comparative analysis of visual census techniques for highly mobile, reef-associated piscivores (Carangidae) , 1986, Environmental Biology of Fishes.

[19]  C. Wilkinson,et al.  Survey manual for tropical marine resources , 1994 .

[20]  W. Gladstone,et al.  Accuracy and bias of visual estimates of numbers, size structure and biomass of a coral reef fish , 1990 .

[21]  Patrice Francour,et al.  Fish assemblages of Posidonia oceanica beds at port-cros (France, NW Mediterranean) : Assessment of composition and long-term fluctuations by visual census , 1997 .

[22]  Michael J. Kingsford,et al.  Studying temperate marine environments , 2000 .

[23]  Byron J. T. Morgan,et al.  Estimating Numbers of Terrestrial Birds. , 1981 .

[24]  M. Shortis,et al.  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 , 2002 .

[25]  G. Caughley,et al.  Analysis of vertebrate populations , 1977 .

[26]  S. Jennings,et al.  Biased underwater visual census biomass estimates for target‐species in tropical reef fisheries , 1995 .

[27]  David R. Anderson,et al.  Distance Sampling-Estimating Abundance of Biological Populations. , 1994 .

[28]  Ganapati P. Patil,et al.  Sampling Biological Populations. , 1982 .

[29]  Euan S. Harvey,et al.  A Comparison of the Accuracy and Precision of Measurements from Single and Stereo-Video Systems , 2002 .

[30]  N. Andrew,et al.  Sampling and the description of spatial pattern in marine ecology , 1987 .

[31]  J. Bell.  EFFECTS OF DEPTH AND MARINE RESERVE FISHING RESTRICTIONS ON THE STRUCTURE OF A ROCKY REEF FISH ASSEMBLAGE IN THE NORTH-WESTERN MEDITERRANEAN SEA , 1983 .

[32]  J. Bell,et al.  Estimating length frequency distributions of large reef fish underwater , 1985, Coral Reefs.

[33]  V. E. Brock,et al.  A Preliminary Report on a Method of Estimating Reef Fish Populations , 1954 .

[34]  Gary A. Kendrick,et al.  Differences in fish assemblages from different reef habitats at Hamelin Bay, south-western Australia , 2003 .

[35]  R. Watson,et al.  Bias introduced by the non-random movement of fish in visual transect surveys , 1995 .

[36]  D. Bellwood,et al.  Interactions amongst herbivorous fishes on a coral reef: influence of spatial variation , 1985 .

[37]  Queensland Townsville.  Observer effects and training in underwater visual surveys of reef fishes , 1997 .

[38]  N. Draper,et al.  Applied Regression Analysis. , 1967 .

[39]  M. Smith.  Effects of observer swimming speed on sample counts of temperate rocky reef fish assemblages , 1988 .

[40]  M. Shortis,et al.  Improving the statistical power of length estimates of reef fish: a comparison of estimates determined visually by divers with estimates produced by a stereo-video system. , 2001 .

[41]  James A. Bohnsack,et al.  EFFECTS OF REEF SIZE ON COLONIZATION AND ASSEMBLAGE STRUCTURE OF FISHES AT ARTIFICIAL REEFS OFF SOUTHEASTERN FLORIDA, U.S.A. , 1994 .

[42]  Graeme Caughley,et al.  Experiments in Aerial Survey , 1976 .

[43]  P. Lavery,et al.  Differences in recreationally targeted fishes between protected and fished areas of a coral reef marine park , 2003 .

[44]  J. Bohnsack,et al.  A stationary visual census technique for quantitatively assessing community structure of coral reef fishes , 1986 .

[45]  H. Marsh,et al.  Correcting for visibility bias in strip transect aerial surveys of aquatic fauna , 1989 .