Jailbreak: a fishway releases the endangered Macquarie perch from confinement below an anthropogenic barrier

Abstract

Management interventions are often needed to facilitate the recovery of ecosystems affected as a result of human alteration. Population-level monitoring is often central to evaluating the effectiveness of specific on-ground actions. In the present study, we assessed the response of a remnant population of the endangered Macquarie perch (Macquaria australasica) to the construction of a rock ramp fishway on the Cotter River, Australia, over a 7-year period. Prior to fishway construction, this obligate riverine spawner had been previously confined to Cotter Reservoir and six kilometres of stream by a raised road-crossing. Surveys conducted in the 2 years following fishway completion failed to detect Macquarie perch upstream of the fishway. Subsequent surveys (6–7 years post-fishway completion) detected Macquarie perch up to 12 km upstream of the fishway. The number and distribution of smaller-sized individuals (0+ (<100-mm total length (TL) and 1+ (100- to >150-mm TL)) suggests that individuals found upstream of the fishway are resident stream fish and not fish that have migrated from known downstream spawning areas. The success of the fishway has been timely because enlargement of a downstream reservoir will inundate four kilometres of river and destroy the majority of spawning sites of this species downstream of the fishway in the Cotter River.