Estimating the abundance of abalone: the importance of patch size

Abstract

A method to assess the patch frequency and so derive estimates of relative abundance and biomass for populations of Haliotis iris is described. The eight populations of H. iris surveyed from southern New Zealand comprised mostly small patches (≤4 individuals). Larger patches were comparatively infrequent but their frequency varied among populations. Application of patch-frequency data to estimate relative abundance was validated with direct counts and a comparison with the collection rates from timed searches. Relative abundance, relative biomass and density were estimated from patch-frequency data. These measurements were more precise and less time consuming than direct estimates of density. The relatively short time per survey allowed replication, giving surveys the power to detect the changes in the frequency of patches expected to result from commercial fishing. A survey method to examine juvenile abundance is also described: abundance was weakly correlated with the frequency of large patches. The relative abundance of juveniles varied among H. iris populations possibly because of differences in wave exposure between habitats.