Document ID: chunk:federal_register_of_legislation:F2023L00138:front:0:p15
Version: federal_register_of_legislation:F2023L00138
Segment Type: other
Provision Reference: 
Character Range: 39401–42472

such as invertebrates.

             The regulation of river flows has the potential to reduce water quality by excessively raising or lowering water temperatures, reducing dissolved oxygen levels and increasing nutrient and contaminant loads (Kingsford 2000). These changes can result from altered flows caused by water diversion, impoundment or sustained dry periods reducing run-off. Water quality can also be impacted by urban and agricultural run-off, which can lead to phytoplankton blooms, reduced oxygen levels and increased salinity.

             Pollution in wetlands is likely to cause a decline in many of the prey species of the Australasian Bittern, such as eels, freshwater crayfish and frogs which in turn may have a negative effect on bittern populations and their health (Marchant and Higgins 1990).

2.2.5     Invasive species

 Invasive herbivores
             Invasive herbivores such as pigs, horses, goats and deer degrade wetlands important for Australian Bittern by digging up wetlands edges and removing vegetation cover. Hard hooved species trample wetland vegetation and have to potential to damage nests (DBCA 2018).

 Predation
             The Australasian Bittern is subject to the predation of eggs and juveniles by foxes (Vulpes vulpes), cats (Felis catus), rats and pigs (Garnett and Crowley 2000; DBCA 2018). Foxes are known to be predators of ground-nesting birds across the range of the Australasian Bittern (NSW National Parks and Wildlife Service 2001), so could be a potential threat

         2.2.6     Loss of genetic diversity
   The estimated number of mature individuals is 1,300 in Australia (Herring et al. 2019a). In Western Australia, the population is estimated to be between 50–100 individuals (DBCA 2018)). A small population is more susceptible to demographic and genetic stochastic events, which can impact the long term survival of the population. Research is required to understand the genetic structure of Australasian Bittern and may be used to identify important populations and appropriate management units.

         2.2.7     Threat prioritisation
   Each of the threats outlined above has been assessed to determine the risk posed to the Australasian Bittern population (Table 3) using a risk matrix (Table 2). This in turn determines the priority for actions outlined below. The threats were considered in the context of the current management regimes. The impact of that threat has been assessed assuming that existing management measures continue to be applied appropriately. If management regimes change then the level of risk associated with threats may also change. The risk matrix considers the likelihood of an incident occurring and the consequences of that incident. Threats may act differently in different parts of the species range and at different times of year, but the precautionary principle dictates that the threat category is determined by the population at highest risk. Population-wide threats are generally considered to present a higher risk.

   The risk matrix uses a qualitative