Destocking waterways: Evidence that stocked Murray Cod (Maccullochella peelii) were extracted at pumped irrigation diversions within 24 hours of release

Abstract

Millions of native fish are entrained into irrigation pumps in Australian rivers every year. It is often assumed these fish are wild, but stocked fish may also be affected. During fish entrainment surveys at two pump intakes on the Macquarie River, New South Wales, a noticeable increase of entrained juvenile Murray Cod (Maccullochella peelii) was observed. DNA parentage analysis confirmed that a large proportion of these fish were linked to nearby fish restocking events. At both pump intakes, genetic analysis confirmed that at least 70% and 17% of the individuals sampled were stocked fish. This equated to up to 3% of the fish that were stocked – most of which were entrained less than 24 h after their release. Given the large number of unscreened irrigation pumps in this reach of river, and more broadly throughout the Murray–Darling Basin, fish losses at pump intakes have the potential to remove large numbers of stocked fish from the river where they are released to support native fish recovery and boost recreational fishing opportunities. The use of fish-protection screens at pump intakes may be a suitable solution to reduce the number of fish entrained and thus increase the survival of recently stocked fish in the rivers.