Preventing Freshwater Turtle Extinctions

In Australia, humans have impacted this
regime because mortality of eggs and young
has increased, primarily because of predation
by invasive foxes, Vulpes vulpes (Thompson
1983), and increased adult mortality through
motor vehicle mortality on roads and direct
predation by foxes on nesting females
(Spencer 2002). In the Murray River in
Australia, mortality rates of eggs by foxes
have increased to over 93% (Thompson
1983; Spencer 2002a). As a result, turtles in
the River Murray are in serious decline, with
abundances 69-91% lower than 40 years ago
(Chessman, 2011). Apart from road deaths
and predation, turtles are also struck by
boats, drowned in fishing nets or in irrigation
pumps, killed by anglers and human
activities that affect water quality are
increasing the prevalence of wildlife diseases
(Kennett et al. 2009).
With multiple threats impacting multiple life
history stages of freshwater turtles, the
dilemma for conservation is the capacity to
implement diverse, broad-scale management
strategies to address each threat. Thus, it is
time to evaluate whether headstarting may
allow for simultaneously managing a range of
threats affecting freshwater turtles. Our aim
is to evaluate a range of management
strategies using Australia’s most common
and widespread freshwater turtle, the
Eastern Long-necked Turtle (Chelodina
longicollis), which is highly mobile and
inhabits wetlands throughout the south-east
of Australia, including cities and urban areas
(Cann 1998). Nest predation rates are high
because invasive foxes occur throughout
their range, but they are also at particular
risk of road mortality and habitat
fragmentation arising from urban
infrastructure (Hamer et al. 2016) because
they frequently move between wetlands
(Spencer and Thompson 2005). They occupy
a wide range of wetland habitats and are a
late maturing species, with males maturing
at 7-8 years of age and females at 10-12
years of age (Kennett et al. 2009). Mortality
of adult turtles can drive species to
extinction (Heppell 1998), and combined
with reduced recruitment levels because of
invasive predators, a species like Chelodina
longicollis may be at particular risk of
extinction. Given their proximity to population
centres, management of their multiple threats
is complex and difficult.
Here we conduct Population Viability
Analyses (PVA) to assess the risk of
extinction of C. longicollis to
increasing adult mortality,
particularly focusing on harvesting of
females, and reduced recruitment
through fox predation. We also model
a range of management scenarios to
test the effectiveness of
headstarting, reduction of nest
destruction via fox management, and
measures that reduce adult mortality
via roadkill.
Chelodina longicollis is the most
widespread freshwater turtle in Australia,
with an extensive range across eastern
Australia (Cann 1998). Their range
broadly overlaps human populated areas
and includes the capital cities of Brisbane,
Melbourne, Canberra, Adelaide and
Sydney (Cann 1998; Kennett et al. 2009).
Chelodina longicollis occupies a wide
range of habitats, such as shallow
ephemeral swamps, farm dams
(Chessman 1988; Wong and Burgin
1997), and flowing rivers (Chessman
1988).
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Spencer R-J et al. 2017 Critically Evaluating Best Management Practices for Preventing Freshwater Turtle
Extinctions. Conservation Biology. In Press.