Standard Talk (15 mins) Australian Society for Fish Biology Conference 2022

Alien invasions: the ecology and movement of tilapia during a new incursion (#26)

Kaitlyn O'Mara 1 , Michael Venarsky 2 , Jonathan Marshall 3 , Ben Stewart-Koster 1
  1. Griffith University, Nathan, QLD, Australia
  2. Department of Biodiversity Conservation and Attractions, Government of Western Australia, Kensington, WA, Australia
  3. Department of Environment and Science, Queensland Government, Brisbane, QLD, Aus

Tilapia are a tropical freshwater fish from the Cichlidae family, native to Africa and the southwestern Middle East. In Queensland, Australia, many eastern draining catchments have been invaded by Mozambique and spotted tilapia. Recently, an incursion of these species was detected in the western draining Mitchell River catchment. Ecological impacts of invasion are not well documented despite the potential for tilapia to negatively impact ecosystems. We studied the spread, population establishment, movement ecology, and habitat and diet preferences of the tilapia in the Mitchell catchment to better understand the ecology of new invasions. To do this we employed a combination of electrofishing surveys, habitat assessments, strontium isotope analysis of otoliths, stomach contents analysis, and stable isotope analysis of tilapia and common native fish. We found that tilapia were present only in one area of the upper catchment with fish found in three distinct locations in the area (two of which were weirs). These locations were rich in macrophytes and had deeper pools. A habitat similarity assessment identified off-channel habitats on the floodplain as high-risk areas for spread and further population establishment. The preference for macrophyte-rich areas is reflective of the herbivorous diet of tilapia, with plant material found to be the dominant food in the study region. Stable isotopes of common native fish showed that food webs in weirs were more similar to those in off-channel habitats than river channels, suggesting that off-channel habitats could support tilapia dietary requirements. Strontium isotopes of tilapia otoliths showed that movement varied between the three locations, with evidence of dispersal to one of the locations from both of the other locations. Overall, the key finding of active dispersal to ideal habitat for rapid population growth provides important insight that can be used to inform monitoring and control strategies.