On a razor's edge: Status and prospects of the critically endangered Bellinger River snapping turtle, Myuchelys georgesi

Abstract

In the summer and autumn of 2015, the Bellinger River snapping turtle (Myuchelys georgesi), a narrow‐range endemic of eastern New South Wales, Australia, suffered mass mortality from epidemic disease, apparently caused by a previously unknown virus. Information on the current population size and structure of M. georgesi, and the body condition and growth of the surviving individuals, is needed to support planning of conservation actions. Population estimates are also needed for a sympatric population of the widely distributed Macquarie turtle (Emydura macquarii), which has probably been introduced to the Bellinger River and may threaten the persistence of M. georgesi through hybridization, competition, and disease transmission. Data from five turtle surveys between November 2015 and November 2018 were used to estimate populations of the two species in the Bellinger River by an analysis based on habitat extent and turtle detectability. Changes in the body condition of M. georgesi and the body growth of both species were also assessed. Current populations of ~150 M. georgesi and ~500 E. macquarii are indicated, although the uncertainty of these estimates is high. The estimate for M. georgesi represents a decline of >90% from the historical population. Moreover, about 88% of the surviving M. georgesi are immature, and only about 5% are mature females. However, the body condition of the survivors has improved recently. Growth models suggest that M. georgesi matures later than E. macquarii, which may provide the latter with a competitive advantage. Evidence presented here does not support a previous hypothesis that M. georgesi were predisposed to disease through malnutrition and consequently reduced immune competence caused by high water temperatures and low river flows. Continuing disease, hybridization, and interspecific competition are probably the greatest threats to the persistence of the species.

Nidoviruses in Reptiles: A Review

“…Ongoing PCR based surveys to provide insight into the prevalence, incidence, and clinical outcomes of apparently asymptomatic individuals following this mortality event are required. Opportunistic sample collection associated with population monitoring surveys presents a cost-effective option for infectious disease detection and monitoring and could be considered for other reptile species ( 46 , 47 ).…”

“…In a single collection of captive pythons, 75% (30 of 40) of infected animals died over a 28 month period ( 20 ) and there is strong indirect evidence BRV was associated with a significant population decline in an endangered turtle population ( 22 ). This decline is estimated to be more than 90% using population estimates generated years prior to the mortality event ( 47 , 92 , 93 ), however the population size of M. georgesi immediately prior to the outbreak is unknown. Specific antiviral treatments for nidovirus infected reptiles have not yet been reported and evidence to support other therapeutic treatments is limited.…”

A creeping threat? Introduced Macquarie turtles and the future of endangered helmeted turtles in southern Australia

“…The population of E. macquarii in the Bellinger River, introduced at least 30 years ago, had the highest CPUE of the four introduced populations and was also captured at a high proportion of sites. This population has expanded from a few individuals in 1990 to $500 at present, while the river's population of M. georgesi has declined from $4,500 to $150 as a consequence of catastrophic mortality from an epidemic in 2015 (Zhang et al, 2018;Chessman et al, 2020). The date of introduction of E. macquarii to the neighbouring Kalang River has not been reported, but it may have been close to the date of introduction to the Bellinger River, given the similarity of proportional occurrence, CPUE, and skewness of SCL between the two rivers.…”

“…The western saw-shelled turtle, Myuchelys bellii, comprises a small, isolated population on a headwater stream just north of the NSW border in Queensland (Fielder, Limpus & Limpus, 2014) and four separate populations in inland headwater river systems of northern NSW (Chessman, 2015). The Bellinger River snapping turtle, Myuchelys georgesi, is confined to the small coastal Bellinger and Kalang rivers in northern NSW (Chessman et al, 2020).…”

“…might ultimately cause local or total extinction of the latter. However, the invasion process has received little attention, except in the Bellinger River (Georges et al, 2011;Spencer et al, 2014;Chessman et al, 2020). This article compares the occurrence, catch per unit effort (CPUE) and population structure of E. macquarii between native populations and introduced populations within the ranges of all three southern Myuchelys spp.…”