Both State and Commonwealth governments in Australia strongly appreciate the need for ecologically sustainable development. A guiding principle of the Coastal Policy, initiated by the Commonwealth government and developed by the States, is that the coast shall be used and developed in a sustainable manner. The Tasmanian government recognises the economic and social benefits associated with a productive aquaculture industry and is highly supportive of its further development. In 1997, in the Tasmanian Premier’s direction statement, sustainable aquaculture development was listed as one of the highest priorities. To this end the Tasmanian State government is actively engaged in facilitating development by ensuring that sufficient area of state water is made available to accommodate industry expansion.
Similarly the finfish aquaculture community is acutely aware of its reliance on the environment and is keen to ensure that future development is sustainable. Salmon farming industry representatives have recently identified an urgent need for clear information on the effectiveness of fallowing as a means of rehabilitating sediments. This information is vital for the optimal management of lease areas and to ensure that production is sustainable.
The development of guidelines for fallowing of sediments associated with marine fish cages, requires further information on the changing sedimentary conditions over smaller spatial and temporal scales than have previously been studied. It also requires that environmental parameters are assessed in relation to conditions prior to each stocking as well as at reference locations. The literature regarding the length of time required for complete sediment recovery is inconclusive; Lumb (1989) and Johannessen (1994) both found significant residual effects 12 months after cessation of farming whereas Ritz et al. (1989) and Wu & Lu (1998) observed what appeared to be more rapid recovery rates. However, these studies all considered recovery to be a return to control conditions, which are representative of areas unaffected by farming. With regard to farm sustainability, it may be more appropriate to determine whether sediments have recovered sufficiently that they can withstand further inputs without undergoing any cumulative progressive deterioration. If fallowing protocols fail to return sediments to this condition, then there is a danger of long-term additive deterioration of the sediment, which may eventually lead to sediment degeneration to such an extent that farming operations become unviable.
References:
· Johannessen, P.J., Botnen, H.B. & Tvedten, O.F. (1994) Macrobenthos: before, during and after a fish farm. Aquaculture and Fisheries Management. 25: 55-66.
· Lu, L. & Wu, R.S.S. (1998) Recolonisation and succession of marine macrobenthos in organic-enriched sediment deposited from fish farms. Environmental Pollution. 101: 241-251.
· Lumb, C.M. (1989) Self-pollution by Scottish Salmon Farms? Mar. Pollut. Bull. 20: 375-379.
· Ritz, D.A., Lewis, M.E. & Ma Shen, (1989) Response to organic enrichment of infaunal macrobenthic communities under salmonid seacgaes. Mar. Biol. 103: 211-214.
