The first large-scale fishery-independent survey of the saucer scallop, Amusium japonicum balloti in Queensland, Australia

Abstract

The saucer scallop. Amusium japonicum balloti, is a valuable component of a multispecies trawl fishery off the Queensland east coast. In recent years, a decline in catch rates resulted in the closure of small areas within the fishing grounds (preservation zones) and the allocation of funding fur a large-scale fishery-independent survey. The first survey based on a stratified random survey design is reported in this paper. The survey found relatively low densities within the strata as compared with similar species in other parts of Australia and elsewhere in the world. The position of two of the three preservation zones was extremely appropriate, because together they contained 20% of the over-all numbers caught in the whole survey. The highest densities in the remaining fishing ground occurred in the inshore north and central strata. The southern sites were characterized by a high proportion of very low or zero density sites. If a previously published gear efficiency parameter on this species and gear is used, then absolute adult abundance values are within the same order of magnitude as the commercial catch, and fishing pressure may be high. The application of this measure of gear efficiency to calculate absolute adult abundance estimates is discussed. Four methods of estimating confidence intervals are discussed. The survey was extremely successful in terms of coverage of the major scallop grounds and production of density estimates with low coefficients of variation.