The feasibility of salmon ranching : a case study on the Rangitata River

Abstract

Deep Stream on the Rangitata River has been provisionally assessed for its feasibility as a salmon ranching site. This was on the basis of physical, biological, technical, engineering, economic and socio-environmental considerations. The salmon fishing in the context of multi-use of the river was examined, and this identified the biggest threat to the fishery as being water abstraction as through the Rangitata Division Race.

Salmon spawning records reveal Deep Stream as the significant habitat in the Rangitata Catchment. Biologically, Deep Stream was confirmed as an optimal spawning habitat and suitable for rearing large numbers of salmon. The flat topography, as surveyed, means that a gravity flow hatchery water supply would need to be artificially created. Deep Stream would be capable of supporting a ranching operation of several production capacities provided that groundwater could be utilised as a supplementary water source. The profitability of the salmon ranching operation was dependent on cost charges to fish feed and labour. Recapture sites closer to the sea increased profitability because fish in spawning conditions up river were likely to be less marketable as flesh. A marketing strategy of eyed egg sales proved most profitable. A national analysis using cost-benefit analysis indicated that policy changes regarding adult recapture downstream of release would benefit both angler and commercial operator.

Environmentally, there would be little impact on the site. Downstream effects of large numbers of smolt releases would be negligible because of the smolts' short residence time in the river. The possible increase in angler numbers during the salmon season could impact on braided river habitat of birds. The social impacts on the local community are not expected to be negative.

A resource-evaluation and use-analysis model was presented and utilised in the above assessment. The model proved worthwhile in enabling the principles of resource management to be applied. The major management issues relevant to this biologic resource were identified as land use, overall water use and resource use as conflict between commercial and recreational uses.