Lake Eyre Basin Rivers 60 permanency of waterholes becomes critical. There are many waterholes of different size and permanency along Cooper Creek (Silcock 2010). Large waterholes with permanent water since European settlement (e.g. Eulbertie Waterhole) are dominated by large mature individuals, with few juveniles and no evidence of recent recruitment (Fig. 5.5a). This represents a climax state where the population has matched the capacity of the waterhole to sustain a turtle population of a certain size. Contrastingly, some waterholes dry completely (e.g. Tanbar Waterhole in 1983 Fig. 5.5b), presumably killing all the turtles. In these waterholes, when they fill up, juveniles, including small individuals, dominate. These waterholes are colonised by a few individuals from more permanent waterholes. They follow an upswing, inevitably followed by a catastrophic decline when the waterhole dries again, perhaps decades later. There is a dynamic built around the different successional waterholes from some completely dry to others remaining as a chain of small pools (e.g. Fish Billabong and Broadwater Billabong in Lochern National Park) and the permanent ones. Turtle sizes and growth rates track this gradient between ephemeral and permanent waterholes. There is added complexity with the variability of floods and their effects on waterhole permanency. All along the Cooper, there are local extinctions of turtles and climax populations from which recruits then colonise waterholes when they fill. These processes unfold over decades, affecting dynamics in the slow lane, but allowing this water-dependent turtle to persist in the desert rivers of the Lake Eyre Basin. Turtle sustainability Natural river flows and flooding have produced healthy but highly dynamic populations of turtles, intricately locked into the dynamics of the rivers. Boom periods are pivotal in their production of widespread flooding, which also produces high productivity of plants and Fig. 5.5. Size distributions of adult (dark grey) and juvenile (light grey) Cooper Creek turtles, measured as carapace length which is a good indication of age from (a) a permanent waterhole on Cooper Creek (Eulbertie Waterhole) compared with (b) a typical waterhole that periodically undergoes complete drying (Tanbar Homestead Waterhole).
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