Dissolved oxygen tolerance of exotic freshwater fish species in north Queensland
Project Leader: Dr Damien Burrows, JCU
Exotic fish species have become increasingly established and dominant in north Queensland freshwater ecosystems in recent years. Research has shown that exotic species have become most abundant in degraded aquatic habitats, in which naturally low levels of dissolved oxygen (DO) have typically further declined. Earlier work funded through this MTSRF project (Webb 2008) showed that the greater tolerance of exotic fi shes to water quality variables such as low DO and high temperature were major contributors to the invasion success of exotic species that had established breeding populations in north Queensland freshwaters. Researchers tested tolerance to low DO in a range of exotic species from those that have established in freshwaters of north Queensland, those that have been found in freshwaters in north Queensland (though not established) and those that are regularly sold in aquarium shops and may thus be released into the environment in the future. Species tested were from four fish families that are freshwater-derived taxa, that is, they have very long evolutionary histories in freshwater, where low DO is more prevalent, compared to most Australian native fish families, which mostly have relatively recent marine ancestry. Fish from the families tested in this study are also commonly used as aquarium fish (the main source of introduced fish species). As expected, it was found that the exotic fishes had significantly greater DO tolerances than most native fish species they would be likely to encounter in north Queensland’s aquatic ecosystems. In addition, we have identified several new species that threaten to invade north Queensland from Papua New Guinea, which are from the families Anabantidae (eg, climbing perch), Channidae (eg, snakeheads) and Osphronemidae (eg, gouramis), all of which are capable of breathing oxygen directly from the air and can stay out of water for considerable periods. Their pre-adaptation for tolerating very low DO confers a considerable risk for their establishment in north Queensland.
A new method for estimating cassowary population size
Project Leader: Dr David Westcott, CSIRO
We know surprisingly little about southern cassowaries (Casuarius casuarius), including even the most basic parameters required for management of this iconic but endangered species. Arguably the most basic data needed to assess the conservation status of a species and its management requirements is an estimate of population size and trends. With the support of the Wet Tropics Management Authority and the Australian Rainforest Foundation, researchers have been developing a monitoring methodology based on DNA fingerprinting of cassowary dung samples. Researchers can now identify and sex individual cassowaries by amplifying DNA from dung samples collected from a variety of locations in the Wet Tropics region. The method makes scientifically rigorous estimation of population size possible, and provides a cost-effective process for community involvement in monitoring of key cassowary populations. Faecal-DNA monitoring methods can be used in two monitoring contexts for cassowaries. The first is in broad-scale surveys of large geographical areas, e.g. the Wet Tropics or the species’ Australian range, with the purpose of population estimation and monitoring of long-term population trends at these scales. The second is as part of intensive population studies of relatively small geographic areas where sampling occurs regularly, effectively resulting in monitoring of the individuals and their use of the local area. In the latter context, community involvement in local-area sample collection has the potential to not only increase the temporal and spatial resolution of monitoring, but to increase the engagement of local communities in conservation activities.
Barriers to fish passage, such as flood mitigation, drainage structures, and extensive road, rail and canerail networks, can have a significant impact on native fish assemblages. We identified artificial physical barriers in the Wet Tropics bioregion, Far North Queensland, Australia, through a desktop GIS analysis of the stream/river and transport networks. A total of 5,536 potential artificial, physical barriers to fish passage were identified in a stream network of 19,764 km at a scale of 1: 100 000. The Mulgrave (1,076) and Johnstone (1,069) basins contained the highest number of potential barriers, whilst most potential barriers comprised road crossings (66%) and cane rail crossings (18%). Due to the unavailability of consistent datasets at smaller scales, we have not identified artificial physical barriers smaller than 50 m. Hence it is very likely that the total number of potential barriers to fish passage in the region is many times higher. We subsequently prioritised the 5,536 potential barriers, to identify those barriers that will provide the greatest habitat value for native fish species when removed and/or mitigated. A total of 104 potential barriers were identified as high priority for rehabilitation, with the Daintree (32), Mossman (19) and Mulgrave (17) basins having the highest numbers. We recommend that the high priority status and attributes of these 104 barriers be verified on-ground, and that rehabilitation of barriers be experimentally examined as a management strategy to improve native fish movement and reduce invasive fish abundance in the Wet Tropics region.
This report by CSIRO and James Cook University researchers is a synthesis of past and current research and management of invasive species in terrestrial and freshwater ecosystems of the Wet Tropics bioregion, North Queensland. Its intention is to identify knowledge gaps and critical research needs and thus recommend future opportunities for investment in research and management of invasive species in the Wet Tropics.