A turtle listed critically endangered in Victoria is spreading through nine Manning River tributaries

The study's authors describe the introduced turtle as a more urgent threat to the Manning River helmeted turtle than the pressures already on its listing ^[4], and hybridization is the one they call most pressing ^[11]. Competition for food and introduced disease reduce a population ^[9]. Hybridization can end the species while the river still holds turtles, because hybrid offspring reproduce quickly and eventually replace the endangered parent population ^[11]. The authors also say research suggests hybridization is not a new phenomenon among Australia's freshwater turtles ^[24].

Current evidence suggests it is already under way in the Bellinger and Kalang rivers, where Macquarie River turtles were introduced in the 1990s ^[12]. That release came at least eight years before the first Manning catchment record in 2007, and as much as seventeen years if it happened at the start of the decade ^[23]. The endemic turtle of the Bellinger, Myuchelys georgesi, is listed as critically endangered, and it and the Manning turtle occur in only two coastal river systems in eastern Australia ^[10].

The Manning turtle's lineage dates back 55 million years, and the Traditional Custodians of Birpai-Barray know it as Guraa in the Gathang language ^[2]. In its own range the introduced turtle is the one being protected: Victoria lists Emydura macquarii as critically endangered and South Australia lists it as vulnerable ^[6]. The species is native to several river systems across Australia ^[5].

Specificity was the design problem. River water can contain the DNA of hundreds or even thousands of species ^[16], so the team compared sequences from their two target turtles against close relatives and other turtles that share the habitat before taking the tests to the river ^[15]. The stated purpose was monitoring the presence of Macquarie River turtles as they encroach on Manning River turtle habitat ^[25].

The field test was small. Turtle ecologists from the Redleaf Group, an Australian environmental company, worked the same river with mask and snorkel, capturing turtles and recording population data ^[19]. The water sampling covered fewer sites than the number of tributaries where the introduced turtle has already been recorded ^[22].

The water samples answer a narrower question than the captures do. The eDNA tests report which species' DNA was in the water ^[15], and the population figures came from the snorkel work ^[19]. Snorkeling, trapping and underwater video are time-consuming and costly, and in some cases they mean turtles are handled by humans ^[14]. For presence work, filtering river water substitutes for catching animals ^[18].