Van Diemen Aquaculture Study

There is a great deal of complexity associated with the analysis of performance of Atlantic salmon in brass nets at Van Diemen Aquaculture (VDA) and it is challenging to succinctly portray the advantages of brass nets based on VDA performance over the last six years – having said that VDA would no longer be a commercially viable Atlantic salmon farm if it were farming in netting technology other than brass nets. It is not possible to make direct comparisons with the performance of other Tasmanian salmon farming operations as there is no access to verifiable performance data from those companies, and the farming conditions at VDA differ greatly from southern Tasmania – research scientists from an international feed company have described VDA as the world’s only “hot water” salmon farm.

Brass nets were first introduced in February 2005 alongside both nylon and galvanized steel nets. They quickly demonstrated many advantages and the phase out of steel nets was completed in March 2007 with the installation of the first URX nets, however the company continues to use nylon nets inside brass nets for the initial stocking of small fish. The raw data on fish performance is available for all year classes stocked since 2002 and allows some limited fish performance analysis.

The transition to brass net technology has allowed VDA to significantly change farm management and production strategies, expand the farm in to a more physically challenging environment, and maintain adequate environmental conditions for the farming of Atlantic salmon despite external factors that on occasions are at the limits for successful culture of salmon.

Background to Van Diemen Aquaculture

Van Diemen Aquaculture P/L is a small privately owned company that farms Atlantic salmon, (Salmo salar), on a single farm site in northern Tasmania. It commenced operations in 1998 at a small trial site approximately one kilometre upstream from the existing site. Farming commenced at the current site in early 2000 with the installation of four steel cages. (See Figure 1) Since 2000 the operation has expanded from 4 to 28 cages (24*24m, volume of 6500 cubic metres per cage), increasing annual production to over 2600 tonnes. The farm is unique in the Tasmanian industry context – it utilizes a steel cage platform with a fixed link to the shoreline enabling vehicular and pedestrian access. The company does not need a fleet of boats to operate, smolt are delivered by pipe direct from shore to cage on arrival, feed is delivered from a shore based storage facility by pipeline to each cage and harvest fish are pumped ashore to a purpose built harvest facility.

Annual smolt intake of 750,000 occurs from April to August, and harvest is from June in the following year to January. Average harvest size over recent intakes has reached 4.3kg ITR (round weight). The site carries mixed year classes for 8-9 months of each year, with juvenile fish held in the relatively calmer conditions inshore, while larger production fish are held in outer farm positions in fast moving water. Van Diemen fish have a distinctive shape to help them cope with life in strong currents, characterized by a condition factor at harvest of 1.6 – 1.8; fish have strong shoulders, firm flesh and fillet recovery up to 2% greater than the Tasmanian industry average.

The annual production cycle is significantly influenced by water temperature and to a lesser degree by fluctuating salinity. Summer water temperatures generally exceed 20oC for at least some of the season, and this has a significant impact on growth potential.

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Report prepared by Michael Hortle, The Aquaculture Advisor