Comparison of methods for sampling populations of ghost shrimp, Trypaea australiensis (Decapoda: Thalassinidea: Callianassidae)

Abstract

Coring and pumping methods, commonly used to determine the abundance and population parameters of burrowing ghost shrimp, were assessed in three widely separated south-eastern Australian estuaries. First, a comparison of two sizes of coring tube (0.04 and 0.07 m 2) revealed no significant differences in catches of the ghost shrimp Trypaea australiensis Dana, nor differences in precision. However, the smaller sized core was consistently more cost effective. Second, when sampling a 0.1 m 2 quadrat, it was found that 12 “pumps” of a suction pump produced significantly higher numbers of individuals at most sites than using either four, eight or 16 pumps. In a third set of experiments, the coring method was compared to the pumping method, in terms of sampling efficiency, abundance estimates and sex ratios of captured ghost shrimp. Pumping was found to be more efficient, catching significantly greater numbers of ghost shrimp per minute than the coring. In addition, pump catches displayed a more normal size distribution than catches from the core and included a wider range of sizes. Sex ratios of catches from coring was 1:1, while catches from pumping were significantly biased toward females (0.71:1). Since female-biased sex ratios are characteristic of many thalassinid populations, this latter result probably reflects actual sex ratios for T. australiensis and not method based size selectivity.