Preventing Freshwater Turtle Extinctions

Reducing Nest Predation
The effect of reducing nest predation rates
is highly dependent on the degree of adult
mortality per year. In areas where adult
mortality rates are high, nest predation
rates must be reduced by 70% to
effectively replicate pre-European
population growth (Fig. 5), but the risk of
extinction still remains at 32% (Table 2). In
populations with lower adult mortality
rates, a 15% reduction in nest predation
rates can replicate pre-European
population conditions; but extinction
probabilities still remain at 20% (Table 2).
Fig. 4. Headstarting as a management option in an
environment where adult mortality is high (2% annual
mortality) and nest predation is high because of foxes.
Population numbers based on pre-European conditions are
shown in black; 5 year pulse headstarting with hatchlings
representing 75% of the initial adult population size in light
grey; 5 year pulse headstarting with hatchlings representing
60% of the initial adult population size in dark grey; 5 year
pulse headstarting with hatchlings representing 45% of the
initial adult population size in grey.
(a)
1
Fig. 3. Headstarting as a management option in an environment
where adult mortality is high (2% annual harvesting) and nest
predation is high because of foxes. Population numbers based on
pre-European conditions are shown in dark grey; Annual
headstarting with hatchlings representing 30% of the initial adult
population size in light grey; Annual headstarting with hatchlings
representing 15% of the initial adult population size in dark grey
(dashed); Annual headstarting with hatchlings representing
7.5% of the initial adult population size in light grey (dashed).
Preventing Adult Mortality
Eliminating adult mortality only from a 2
population does not reduce the risk of
extinction (Table 2). Populations still decline
with high nest predation rates even if old age
is the only source of female mortality (Fig. 6).
Fig. 5. Population numbers based on pre-European conditions
are shown in dark grey. (a) Adult mortality rates at 2% per
year. Nest predation rates are reduced to 25% (dotted line);
50% (light grey) and 65% (grey) (b) Adult harvest rates at 1%
per year. Nest predation rates are reduced to 80% (dark grey);
85% (light grey).
Table 3. Review of available literature assessing efficacy of standard fox control methods in Australia.
(b)
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Spencer R-J et al. 2017 Critically Evaluating Best Management Practices for Preventing Freshwater Turtle
Extinctions. Conservation Biology. In Press.