Utility of a modified lightweight recreational scallop dredge for surveys of estuarine ark clams (cockles)

Abstract

Arcid cockles support extensive subsistence, recreational and commercial fisheries across the world. In south-eastern Australia, there is minimal published research and a lack of quantitative surveys for the primary harvested species, Sydney Cockle Anadara trapezia, with which to inform management of the resource. Here, we describe the modification and application of an off-the-shelf lightweight recreational scallop dredge for conducting scientific surveys of arcid clams in estuarine soft sediment habitats. Specifically, we look at performance of the gear for sampling medium-large (>45 mm shell length) cockles, and report on the outcomes of preliminary trials of the gear for surveying Sydney Cockle. Efficiency trials showed that the gear captured and retained ∼95% of the cockles in the tow path, however efficiency decreased in compacted sediments (∼66%). Trial surveys captured cockles between 33 and 78 mm shell length, at densities as high as 186 individuals 100 m−2. The modified scallop dredge provides a robust and portable (∼10 kg weight) fishing gear for sampling estuarine soft sediment habitats from small vessels. Both the sampling gear, and the methodology presented here, are broadly applicable for surveying arcid cockles and other bivalve species from similar soft sediment habitats elsewhere.