A Comparison of Three Methods for Visually Assessing Reef Fish Communities: Time and Area Compensated

Reef fish assemblage survey results using Transect, Point, and Random in situ visual assessment techniques were evaluated and compared on a coral reef biotope off the southwestern coast of Puerto Rico. Parameters compared were: number of species, number of individuals, and species diversity (H'). No significant effect attributable to the time-of-day when the surveys were conducted was noted to occur. Variability in observations between divers was not noted for any of the dependent variables while conducting the Transect method. Divers using the Random technique recorded the highest number of species per survey, while the assemblage parameters recorded using Transect and Point methods were statistically similar for most dependent variables. Point surveys, however, had a higher and less variable species diversity. When the data were adjusted for amount of survey time and area it was determined that divers were more efficient in sampling numbers of individuals when using the Transect method. Recently, an interest has developed in the underwater visual assessment of reef fishes (e.g., Barans and Bartone 1983; Harmelin-Vivien et a/. 1985). This interest is due to several reasons as natural reefs serve as important biotopes for testing evolutionary/ecological hypotheses (see Bartone eta/. 1986 for a partial review). Additionally, to assess the relative "health" of natural reefs in terms of productivity, accurate community data are required. Furthermore, advances in the technology of artificial reef design (Buckley et a/. 1985) depend on the development of accurate, quantitative data on fish community abundance and biomass (Bohnsack and Sutherland 1985). Visually gathered reef fish abundance data avoids the substrate disrupting effects of traditional, surface tended collecting devices such as trawling (Bardach 1959). However, a plethora of problems make reef fish assemblage 'Biology Department, University of West Florida, Pensacola, FL 32514, U.S.A. 2Department of Marine Sciences, University of Puerto Rico, current address: Bureau of Marine Research, Florida Department of Natural Resources, 100 Eighth Avenue SE, St. Petersburg, FL 33701, U.S.A. 3 lnstitute for Statistical and Mathematical Modeling, University of West Florida. 85 assessment by any general method difficult. These problems stem from the " . complexity and numerous inherent attributes of reef fish life histories . " (Bartone et a/. 1986:1) involving their behavior and their utilization of spatially irregular reef substrates. Additionally, there are logistical and analytical constraints inherent in each of the in situ visual techniques developed to date. These include difficulties in implementing some methods under less than ideal conditions such as poor visibility, strong currents, or especially irregular substrates. Some methods suffer from diverrelated problems such as difficulties in manually recording data, accuracy of species identification, and diver fatigue. These problems, coupled with the previously mentioned behavioral aspects of the fauna such as secretive habits, schooling, and competitive interactions, illustrate the need to develop visual census techniques which permit accurate and efficient assessment of reef fish assemblages. Many visual techniques for the assessment of reef fish assemblages have been implemented since Brock's (1954) pioneering study of Hawaiian fishes. Most of them have not been 1 Bortone et al.: A Comparison of Three Methods for Visually Assessing Reef Fish Co Published by The Aquila Digital Community, 1988 86 Bortone, S. A. , J. J. Kimmel, and C. M. Bundrick tested or verified for suitability and/or accuracy and often merely reflect a researcher's personal preference. Several recent studies have, however, attempted to objectively compare some methods (e.g., Bartone et a/. 1986, Brock 1982, DeMartini and Roberts 1982, Kimmel 1985, Sanderson and Solonsky 1986). These studies have used various visual methods to assess fish abundance and employed several analytical techniques to clarify some problems but there remains no clear consensus as to what method is the "best" for all or any specific set of conditions. To help answer this methodological question, two observers compared six different methods under a variety of reef conditions (Bartone eta/. 1986). The conclusion of that study was that all of the compared methods are roughly equivalent in their ability to qualitatively describe a fish assemblage. Methods that produce the most information (i.e., number of species and number of individuals) tend to have less variance and more accurately associate environmental parameters with a particular assemblage. Also, the amount of sample time (and perhaps area) appears to be the most significant variable affecting the similarity of assemblage assessments, regardless of method. This suggests that, of the methods tested, those which produce the greatest amount of information in the least amount of time (or area surveyed) would be the most effective. Given that conventional scientific diving is monitarily expensive and constrained by depth-duration relationships, it is extremely important to develop techniques for in situ visual assessments which are efficient for these attributes. It is also imperative to know precisely how important the variables of time and area are to each method. This may allow future researchers to make adjustments or transformations in their data to permit accurate comparisons with other studies for which data were gathered using methods varying in the time or area surveyed. The purpose of this study was to identify the significance of time and area among various visual assessment methods. This was accomplished by employing three different visual assessment techniques in a single location while recording the amount of time and area surveyed by each technique and by analyzing our data in ways that allowed us to evaluate the utility of the various visual methods for assessment of reef fish assemblages.