Growth and mortality in an isolated bed of saucer scallops, Amusium japonicum balloti (Bernardi)).

Abstract

Saucer scallops, Amusium japonicum balloti found in the vicinity of Bundaberg, Queensland in November 1977 were separated both spatially and by depth from other scallop beds and were of relatively uniform size, suggesting they may have originated from a discrete spatfall. These scallops existed in an elongated bed
with the longer axis lying parallel to the prevailing tidal flow. Growth of scallops in the bed was modelled using a von Bertalanffy curve, with parameter estimates such that L t (mm)=105.5 (1-e-0·0448t) with t in weeks. Tagging experiments indicated that movement by individual scallops was limited and that no population movements occurred. A weekly instantaneous natural mortality coefficient was estimated at 0.097, which is sufficient to suggest extinction of the bed in approximately one year, and which is much greater than in other scallop populations studied. The high incidence of the ascaridoid nematode Sulcaris sulcata and the high mortality rate of scallops were speculatively linked with a high density of loggerhead turtles Caretta caretta in the study area.