Measuring abundance of juvenile abalone, Haliotis rubra Leach (Gastropoda : Haliotidae); Comparison of a novel method with two other methods

Abstract

An underwater venturi-suction sampler is described, suitable for sampling fauna on structurally-complex sublittoral reefs. Abundance of juvenile Haliotis rubra was estimated from the samples collected with the suction sampler; this was compared with estimates obtained at the same time by two other methods, an anaesthetic method and a searching method. Off Sandpatch Point (south-eastern Australia) during January 1987, the mean number (s.e.) of H. rubra per square metre of substrate was 68.7 (s.e., 39.2) by the suction method, 25.6 (s.e., 16.1) by the anaesthetic method and 7.7 (s.e., 3.0) by the searching method. Off Cape Schanck, the respective numbers were 1.3 (s.e., 0.5), 1.2 (s.e., 0.5) and nil. Juveniles found in the population off Sandpatch Point were of a size range (430-1020 µm) consistent with recent settlement of H. rubra. The suction method has three main advantages over the other two methods: unlike the anaesthetic technique it is not destructive and is not restricted to removable substrate; it is readily applied to most reef substrata by one diver spending relatively little time under water; and the sampler is sufficiently powerful to remove all juvenile abalone from the reef surface.