Reintroduction of the trout cod in southeastern Australia: perseverance pays off

Summary

Trout cod (Maccullochella macquariensis), a long-lived apex predator of Australia's Murray-Darling Basin, declined so severely from river regulation, invasive fish and overfishing that by 1990 it survived only along roughly 50 km of the Murray River plus two small translocated populations, prompting Australia's first national recovery plan for a freshwater fish in 1994. State fisheries agencies in New South Wales and Victoria developed hatchery breeding programs from the mid-1980s, protected the two remnant wild populations from recreational harvest, and ran public education to help anglers distinguish trout cod from the similar Murray cod. Stocking scaled up through the 1990s to an average of 109,350 hatchery-bred fingerlings released annually between 1996 and 2005 (though production later declined to about 32,450 a year from 2006-2016), guided by a population model and a coordinated national Freshwater Fish Recovery Team of state and federal scientists and hatchery managers; more than 1.71 million fingerlings had been released by 2016, alongside habitat rehabilitation such as reinstating woody instream structure. Long-term monitoring detected wild recruitment in several catchments (Goulburn, Ovens, Mid and Upper Murrumbidgee, Cotter) from the late 1990s into the mid-2000s, though genetic sampling later found hybridization with Murray cod in the Upper Murrumbidgee, and a millennium drought caused fish kills that set the program back. Recovery Team funding lapsed in the early 2000s, and hatchery production has since been diverted partly toward new recreational fisheries. The project rates itself successful, crediting a coordinated multi-jurisdictional approach, sustained hatchery capacity, a guiding population model, and long-term scientific commitment despite funding setbacks.