Degree Name

BEnviSci Hons




School of Earth & Environmental Sciences


Andy Davis


For present and future conservation and management programs to be successful in mitigating the spread of the invasive species, Gambusia holbrooki, in freshwater systems, it is imperative for us to understand their patterns of dispersal and mechanisms of establishment. Understanding how this species disperses and establishes in a range of freshwater environments will allow for a more thorough understanding of their movement and thus will contribute to more effective management strategies. The present study aims to determine how physical and chemical barriers affect the dispersal potential of G. holbrooki in freshwater systems in the Sutherland Shire, NSW, and whether this species has the capacity to re-establish in the short-term in environments they previously inhabited. By using the tag-release-recapture method (Peterson, 1896), visible implant elastomers (VIE) were administered to 700 fish, split into two different populations (red and yellow) that were separated by a trash-rack barrier at each of the two creek sites. Re-capture efforts occurred weekly for 9 weeks, with the movements of the two populations recorded at each site at each location. Re-establishment estimates were determined weekly using presence-absence based observation, by haphazardly netting in areas previously inhabited by G. holbrooki. Results of this study highlight that there was no chemical barrier, or natural physical barrier present that hindered G. holbrooki’s dispersal potential or their ability to re-establish in creeks previously inhabited; even in sites with considerable evidence of petrochemical pollution. However, this study did highlight that anthropogenic barriers such as trash racks have the ability to hamper the dispersal of G. holbrooki, providing the rack has at least a moderate amount of trash accumulated. Results also highlighted that G. holbrooki populations were apparently unable to re-establish in areas they previously inhabited within the short term. The mosquitofish populations have shown variation in their dispersal pattern depending on site specific influences such as the number and type of barriers, the physico-chemical conditions, landscape structure, and trash rack condition. This provides the first demonstrative link between G. holbrooki and the effect of both physical and chemical barriers present in urbanised freshwater systems in the Sutherland Shire. The implication this would have on conservation and management strategies includes devising approaches towards successful mitigation of G. holbrooki dispersal in various freshwater systems in NSW.