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Baited remote underwater stereo-video (stereo-BRUV) stations and diver operated stereo-video (stereo-DOV) transects are increasingly used to sample both tropical and temperate fish assemblages. Compared to in situ visual census methods, the use of stereo-video reduces interobserver variability, improves definition of the sample unit area, increases accuracy of fish length estimates and provides a permanent record of the assemblage that can be validated where required or independently reanalysed. Previous studies have suggested that stereo-BRUV collects representative data on both carnivorous and herbivorous species and can be more cost-efficient than diverbased survey methods. This study compares estimates of common fish assemblage metrics obtained with stereo-BRUV stations and stereo-DOV transects across 3 biogeographic regions, and uses a costoptimization procedure to compare the efficiency of these 2 methods. Stereo-BRUV stations were found to sample greater species richness and obtain greater estimates of relative biomass of generalist carnivores, but no differences occurred in the biomass of herbivores sampled by the 2 techniques. Stereo-BRUV stations generally obtained estimates of assemblage metrics with less variance, resulting in greater power to detect spatial and temporal changes in the fish assemblage metrics. Cost -benefit analyses found that stereo-BRUV was generally more time efficient than stereo-DOV transects in terms of smaller standard error around the mean of the various metrics considered. However, across the 3 biogeographic regions sampled there was considerable variation in the magnitude of these differences. Results suggest that stereo-BRUV stations are, in general, a more cost-effective method for monitoring fish assemblages than stereo-DOV transects.KEY WORDS: Cost -benefit · Power to detect change · Biogeography · Baited remote underwater stereo-video · Diver operated stereo-videoResale or republication not permitted without written consent of the publisher Biol 9: 155-168, 2010 replicates and sites from pilot study data and, therefore, can also be used to evaluate the cost-effectiveness of different sampling methods.The complete sampling of reef fish communities in shallow waters is only possible using destructive methods. Indiscriminate methods such as dynamite have historically been used (Stephan 1904); however; the use of fish toxins such as rotenone (Krumholz 1948) have allowed more discrete and quantitative samples of the fish assemblage to be collected from complex habitats (Robertson & Smith-Vaniz 2008). Recent advances in diving technology have allowed these methods to be used to depths of 150 m, resulting in the description of large numbers of new cryptic species and observations of higher rates of endemism in deeper compared to shallow reefs (Pyle 2000). However, for most largescale studies, sampling the complete fish assemblage is likely unnecessary (Clarke & Warwick 1998) and destructive methods bias future samples obtained from the same locality and can compr...

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Using remote underwater stereo-video systems we examined fish behaviour towards a stationary SCUBA diver at temperate (Rottnest Island) and sub-tropical (Houtman Abrolhos Islands) reefs in Western Australia. Changes in species richness, relative abundance, fish length, and the mean distance of individual fish from stereo-video cameras, in the presence and absence of a SCUBA diver, were assessed to infer changes in behaviour. Results show that a stationary SCUBA diver may obtain accurate measures of species richness and of the composition of fish assemblages in an area. However, the usefulness of these measures to reflect changes in fish behaviour appears limited as responses of fish towards the stationary SCUBA diver were highly species specific. Several species differed in their mean relative abundance (Heterodontus portusjacksoni, Coris auricularis, Thalassoma lunare), length (Ophthalmolepsis lineolatus, C. auricularis), and the distance to which they would approach the stereovideo systems (Kyphosus sydneyanus, Scarus schlegeli) when a SCUBA diver was present. Here, speciesspecific changes in the behaviour of several common and abundant fish species towards a stationary SCUBA diver advises caution to avoid biases when interpreting results obtained by SCUBA divers.

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