Quantifying Relative Diver Effects in Underwater Visual Censuses

Diver-based Underwater Visual Censuses (UVCs), particularly transect-based surveys, are key tools in the study of coral reef fish ecology. These techniques, however, have inherent problems that make it difficult to collect accurate numerical data. One of these problems is the diver effect (defined as the reaction of fish to a diver). Although widely recognised, its effects have yet to be quantified and the extent of taxonomic variation remains to be determined. We therefore examined relative diver effects on a reef fish assemblage on the Great Barrier Reef. Using common UVC methods, the recorded abundance of seven reef fish groups were significantly affected by the ongoing presence of SCUBA divers. Overall, the diver effect resulted in a 52% decrease in the mean number of individuals recorded, with declines of up to 70% in individual families. Although the diver effect appears to be a significant problem, UVCs remain a useful approach for quantifying spatial and temporal variation in relative fish abundances, especially if using methods that minimise the exposure of fishes to divers. Fixed distance transects using tapes or lines deployed by a second diver (or GPS-calibrated timed swims) would appear to maximise fish counts and minimise diver effects.

基于潜水员的水下视觉普查（Underwater Visual Censuses, UVCs），尤其是样带调查法，是珊瑚礁鱼类生态学研究的核心工具。然而这类技术存在固有局限，难以获取精准的定量调查数据。其中一类问题即为“潜水员效应”（定义为鱼类对潜水员的行为反应）。尽管该效应已得到学界广泛认知，但其具体影响尚未被量化，分类学差异的程度也有待进一步探明。为此，本研究针对大堡礁的礁鱼群落开展了潜水员效应的相对影响分析。采用常规UVC方法开展调查时，7类礁鱼的记录丰度均受到SCUBA潜水员持续在场的显著影响。整体而言，潜水员效应使记录的个体平均数量下降了52%，部分类群的个体数量降幅最高可达70%。尽管潜水员效应已成为显著的研究局限，但UVC仍是量化鱼类相对丰度时空变化的有效手段，尤其当采用降低鱼类与潜水员接触概率的调查方法时效果更佳。由第二名潜水员布设卷尺或测绳的固定距离样带法（或经GPS校准的计时游泳法），可最大化鱼类计数结果并最小化潜水员效应的干扰。