Preventing Freshwater Turtle Extinctions

Our models demonstrate that headstarting would be an effective and cost-efficient primary
management tool in a broad-scale integrated conservation plan for C. longicollis. There is no
well recognized and accepted definition of headstarting. The IUCN-SSC (2013) states that
head-starting reptiles "avoids the heavy mortality of young age classes in the wild; wild
hatchlings are reared in protective enclosures before release at less susceptible size/age".
Burke (2015) redefined headstarting as the practice of protecting especially vulnerable life
stages of a species to increase the likelihood of survivorship for conservation purposes.
Success of population manipulations such as reintroductions and head-starting requires
appropriate planning to minimize negative genetic and disease consequences, as well as
impacts to other native species. Captive populations are subject to problems such as
inbreeding depression, loss of genetic diversity, and adaptation to captivity. Thus, it is
important to manage captive populations in a way so that introduced individuals resemble
the original founders as closely as possible, increasing the probability of success (Kleiman et
al. 2010). With critically endangered species, this is extremely difficult given the low
numbers, and likely genetic diversity, of breeder animals. Still, headstarting programs with
small captive populations of Galapagos tortoises have proved successful at restoring
population numbers in some situations (Jensen et al 2015). Importantly, headstarting as a
preventative tool must also be tuned to maintain genetic diversity across a wide area
(Jensen et al 2015). In cases where turtles are declining due to nest predation by invasive
predators, like C. longicollis, developing suitable harvest populations in situ is the key. Many
common species of turtle occur in integrated wetlands and water treatment plants (eg.,
constructed wetlands) throughout their range, and these facilities may provide a tool for low
cost headstarting programs for widespread but declining populations.
Constructed wetlands are small water bodies that have enormous biodiversity potential. The
Integrated Constructed Wetland (ICW) concept is a refinement of storm and wastewater
treatment and effluent reuse facilities, where water and effluent are treated through a series
of ponds. Final tertiary treatment ponds can contain some of the highest aquatic biodiversity
in a region, and well-designed wastewater treatment and effluent reuse plants are potentially
important sanctuaries for local biodiversity, including turtles. They often also have existing
infrastructure including fences, roads, etc. that facilitate protection from invasive species like
foxes. The reproductive potential of turtle populations in constructed wetlands therefore
represents a potential pre-existing resource for developing localized headstarting programs in
situ.
Fig. 9. Graphic demonstration of how one harvest population can supply a large region of turtles each year for headstarting. Each population
Spencer R-J et al. 2017 Critically Evaluating Best Management Practices for Preventing Freshwater Turtle
represents a water body on the landscape, the size of which is random. The dark grey population represents a potential harvest population,
where Extinctions. hatchlings can Conservation be translocated Biology. to surrounding In Press. populations (light grey) to eliminate extinction risk and maintain population growth at
pre-European settlement levels. One hectare of turtles can supply enough hatchlings to release into 25ha elsewhere.
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