A \"feet digging\" swash zone sampling method for the sandy beach bivalve Donax deltoides (Bivalvia: Donacidae)

Abstract

A \"feet digging\" method for sampling the sandy beach bivalve Donax deltoides was evaluated by comparison to quadrat-based results from eleven beaches in subtropical eastern Australia. The method was developed from a recreational fishing technique that involves twisting ones feet into the thixotropic sand to dislodge buried clams which are then recovered by hand. Several plots are sampled across the swash zone in one five-minute sampling unit and the process is replicated at several locations along the beach. Mean feet digging clam counts were proportional to mean transect linear clam densities (r = 0.98). Clam length-frequency distributions from feet digging were similar to those from quadrat sampling except that feet digging was not effective for clams < 16 mm. Feet digging counts are sensitive to both across shore (tidal) and alongshore variation in clam abundance and were less precise than those from quadrat-based methods (CV 1.2x larger). However, feet digging is fast and the method should be useful for low cost surveys of Donax deltoides and similar \"surf clams\".