Preventing Freshwater Turtle Extinctions

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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. 12
Constructed wetlands could be used as breeder facilities for headstarting turtles throughout a local region, where the genetic diversity of turtles within the constructed wetland suitably matched that of natural wild populations. Our models show that a single population of females could supply enough hatchlings to supplement 25 other similar sized populations at an annual rate to maintain population growth at pre-European levels and completely eliminate the risk of population extinction. A simplistic model where relative turtle densities are based on surface area of water demonstrates that all eggs/hatchlings collected from 1 ha of water can provide sufficient numbers of turtles to headstart ~25 ha of water in a region (Table 4; Fig. 9). Our models also demonstrate that periodic increases in recruitment can sustain populations, potentially allowing populations in a region to be managed in a mosaic fashion. In other words, not all populations need to be actively managed each year. In conclusion, we demonstrate a theoretical basis for why headstarting programs are a useful conservation strategy for stopping the declines of freshwater turtles, especially those primarily threatened by both adult mortality (due to roads, predation, or harvest) and invasive predators affecting multiple life history stages. Chelodina longicollis is Australia’s most common species of freshwater turtle but it is clearly at risk because of adult female mortality rates and reduced juvenile recruitment. Its longevity has hidden the impact of these threats, but Australia is now at the stage since post-European settlement where the effects of foxes and urban population sprawl (and associated infrastructure) are being observed through large declines of the population of adult turtles. While ours are predictive models, they reflect what is occurring in some populations, where there have been declines of up to 91% (Chessman 2011). Perhaps it is time to introduce headstarting as a primary management tool for actively managing declining turtle populations, rather than as a tool that is only used once a species becomes critically endangered. Acknowledgements We thank Heather Cameron and the Murray River Turtle Team for their support, as well as, many other colleagues for constructive discussion on this subject. Financial support was provided by the Australian Research Council Linkage Grant Program (LP150100007), North- Central Catchment Management Authority, Yorta Yorta Aboriginal Corporation, Foundation for National Parks and Wildlife, Victorian Department of Land, Environment, Water and Planning, Winton Wetlands, Turtles Australia, Inc. and Save Lake Bonney Group Inc. TurtleSAT is supported by the Invasive Animals CRC and NSW Department of Primary Industries. We especially thank Peter West and Michael Newton (Newton Green Technologies) for on-going support. We also thank Turtles Australia for their ongoing support of TurtleSAT. 13 Spencer R-J et al. 2017 Critically Evaluating Best Management Practices for Preventing Freshwater Turtle Extinctions. Conservation Biology. In Press. https://www.youtube.com/watch?v=WNdGs2H2P8g
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Preventing Freshwater Turtle Extinctions

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