Optimising management actions for the conservation of threatened species in Kakadu National Park: Background Paper for Kakadu National Park Threatened Species Strategy

Kakadu National Park is important for the conservation of very many threatened species, and the conservation of such species is a clear commitment under the Park’s Plans of Management. However, at least some of these threatened species are declining in Kakadu, suggesting that current management actions may not be optimal. Given the large number of threatened species, occurring across diverse habitats and affected by a wide range of threats, there is a large array of potential management actions that could, or need to, be implemented. However, resourcing for such management is finite, so there is a need to prioritise management actions in order to most cost-effectively make a substantial contribution to the conservation of threatened species. This report describes aspects of such prioritisation, following an approach previously used for management prioritisation for conservation in the Kimberley and Pilbara (Carwardine et al. 2011; Carwardine et al. 2014). This report provides advice rather than a single definitive answer. One of its main conclusions is that the optimal management solution depends very much on the objective, and that there are many nuanced variations in objectives – e.g. whether the objective is to achieve the greatest benefit across all threatened species, the least likelihood of species becoming lost from Kakadu, the greatest likelihood of maintaining secure populations of species in Kakadu, and the extent to which these objectives are framed by budget constraints. In this report, we consider all 75 threatened species that have been reported from Kakadu, along with 103 Near Threatened and 13 culturally significant species. Species are attributed values according to their conservation status, taxonomic distinctiveness, ecological significance and cultural value (and a combination of all of these attributes), and – in some analyses here – management actions that particularly benefit higher value species are accorded more weight. A panel of 20 experts provided estimates of the likelihood of persistence (on a 0 to 100 scale) in Kakadu of all 191 species over a 20-year period under current management, under no management (i.e. abandonment) and under each of 7 existing and 35 possible candidate management actions. These actions were developed to encompass a wide range management options for putative threats for all species, and experts also rated the feasibility of the management action being implemented successfully. For every candidate management action, cost (over a 20-year period) was also estimated, based largely on budgetary information or current Kakadu management activities. This costing is difficult to define explicitly because (i) current budgeting in Kakadu does not partition expenditure specifically towards threatened species’ conservation activities; (ii) many management are undertaken for multiple purposes and it is difficult to segregate out a component directed towards threatened species specifically; (iii) the costs and feasibility of some management actions is contingent on other actions (e.g. fire management will be substantially influenced by the control or otherwise of invasive pasture grasses); (iv) some of the candidate management actions may have highly variable costs depending upon contingencies (e.g. general weed biosecurity may be low in most years but may be high if a new outbreak of a highly invasive weed is detected); and (v) some candidate management actions have not been undertaken or implemented at large scale previously, so cost estimates may be partly conjectural. The experts considered that current management in Kakadu was benefitting most (but not all) of the species considered. Under no management, 13 species are considered unlikely to persist (i.e. persistence estimate 80%), the number of species that need to be considered increases substantially (e.g. the number of species with persistence estimates over a 20-year period of Across all species, the individual candidate management actions with greatest benefit (i.e. increase in persistence estimates above the level of persistence under no management) are strategic fire management in the lowlands and in the Stone Country (aiming to increase the extent of longerunburnt habitat), broad-scale reduction of feral cats, and ex situ conservation and translocation of threatened plants. The ordering of actions according to their benefit varies substantially among different taxonomic groups of species. The relative ordering of candidate management actions changes appreciably when feasibility and cost is considered. Actions with high benefit:cost include control of gamba grass, general weed biosecurity, local-scale intensive control of cats, cat-proof exclosure fencing, pig-proof exclosure fencing, buffalo control, toad-proof exclosure fencing, the management of Indigenous harvest, and ex situ conservation and translocation of threatened plants. This analysis uses Marxan to derive best sets (most cost-effective solutions) of management actions under a range of persistence targets (from 50% to 90%) and budget caps (from $20 m to $150 m over a 20-year period). The optimal mix of management actions, and the success rate (number of species meeting the persistence target) varied considerably across these scenarios. Solutions for scenarios with low persistence thresholds typically involved fewer, and mostly relatively inexpensive, management actions, and provided relatively little benefit across species generally. The number of species meeting persistence threshold targets under the optimal set of management actions was modelled across a threshold target levels and budget caps. This modelling suggests that a 20-year budget of c. $35-40 million is required if the objective is to retain all species with a persistence estimate of at least 50%, of c. $140 million is required if the objective is to retain all species with a persistence estimate of at least 60%, and of c. $220-230 million is required if the objective is to retain all species with a persistence estimate of at least 70%.