Use of acoustics to assess a small aggregation of orange roughy, Hoplostethus atlanticus (Collett), off the eastern coast of Tasmania

Abstract

A relatively small aggregation of orange roughy (Hoplostethus atlancticus) was located in April 1989 off the eastern coast of Tasmania. A Simrad EK400 (38 kHz) scientific echo-sounder was used to survey the aggregation over a period of eight days, during which time the aggregation was commercially fished. The aggregation was confined to an area of approximately 4 km², with the dimensions of the aggregation varying within and between days. High densities of orange roughy were located near the bottom on some days and more than 24 m off the bottom on others. Average fish densities during the survey and an estimate of the extremes of densities (fish m^-3) are presented. Estimates of the original biomass of this aggregation as obtained from acoustic data and commercial catch-and-effort data are compared, and the mean target strength of the population is estimated.