Acoustic methodologies are important tools for monitoring deep-water fish and have the potential to provide high-precision estimates of aggregation size. However, they can be costly to design and implement for monitoring fish. Data from 2 years of scientific surveys of the spawning aggregations of orange roughy (Hoplostethus atlanticus, Collett, 1889) on the Cascade Plateau, Tasmania, collected using commercial fishing vessels and echosounders, were used to develop a cost-effective approach for estimating the size of deep-water aggregations. Criteria were developed to standardise the identification of orange roughy echo-traces from acoustic data from 23 surveys in 2001 and 19 in 2005. The spawning condition of the fish was monitored simultaneously with the acoustics in each year (n = 29 trawls each year). The volumes of the aggregations were estimated throughout the survey period. Although the precision of the estimated aggregation size is low, large amounts of data can be collected over extended periods by using this approach and the equipment on standard commercial fishing echosounders. Aggregation volumes varied markedly during each spawning season and changes in volume appear to be linked to the spawning biology. Monitoring the spawning biology, therefore, provides crucial complementary information for interpreting estimates of aggregation size from acoustic surveys.
A cost-effective alternative for assessing the size of deep-water fish aggregations