Prospects for a restorative fishery enhancement of Lake Kununurra: a high-level tropical impoundment on the Ord River, Western Australia

Abstract

The high-level irrigation water supply dams of the Ord River in tropical Western Australia impede the movement of Barramundi Lates cafcarifer and other tropical fish species. A recreational Barramundi fishery enhancement of Lake Kununurra using a fishway has been widely promoted as advancing fishery conservation and the reformation of land and water management practices within the greater Ord River region. Of the fishways considered here, none have been found to admit Barramundi in the numbers and size classes necessary to establish or maintain the recreational fishery. Reasons for this include an inadequate understanding of fish behaviour and/or fishway deSign faults. The seemingly reluctant use of fishways by Barramundi might also be confounded by some observations being made on rivers where Barramundi populations are either comparatively small or non-existent. The alternative to a fishway is hatchery stocking. This option, like a dedicated Barramundi fishway, represents a single-species approach to fishery enhancement and is the least legitimate attempt to restore the ecological integrity of the fish communities of either Lake Kununurra or the Ord River. We argue that progress toward the restoration of the lake should continue, though a fishery enhancement programme that incorporates the broader fish community and not just a single species, would better rebuild the presently degraded Ord River system. Of the available options, we recommend testing an experimental model that incorporates aspects of the vertical-slot and bypass fishway designs, with the objectives being to learn migratory fish behaviour, abundance, and patterns and cues for fish movement. This approach can incorporate Barramundi as the target species to better understand entrance design constraints, minimum slot widths for larger fish, and operation under low flows during peak irrigation water demands, but still accommodate the movement of tropical fishes during these periods.