Native fish populations within the Murray Darling Basin (MDB) have dramatically declined in richness and abundance over the past century. This decline is partly attributed to river regulation and the pervasive impact of carp (Cyprinus carpio). The biology and ecology of this invasive species provides them with a competitive advantage over native fish and has contributed to their dominance of fish communities in many river systems of south-eastern Australia.
The Ovens River Demonstration Reach (ORDR) program (2008-2017) incorporated carp removal (via electrofishing) as a river rehabilitation strategy in 2014 to improve native fish populations within a 20km reach of the Ovens River. As the impact of carp removal on native fish could not be separated from the cumulative impacts of recent works, an investigation into the impact of carp removal on the ORDR carp population was undertaken. A total of 521 individual carp were removed over three years (2014 to 2016) from 10 sites. Greater numbers of carp were removed during years of high abundance; however, carp abundance across years was highly variable.
Our hypothesis that a ‘50% reduction in the total (captured and observed) abundance of carp in each sample year would result in a significant decline in carp numbers in consecutive years’ was not supported. The impact of flows, native fish, wetland/channel connectivity, competition and cohort structure across years are discussed to explain our findings.
Engagement with the community and relationship building between ARI with CMA’s, local landcare, fishing clubs, water operations managers, MDBA staff, Office of Water, Nutrisoil and community action groups has been a huge success throughout the ORDR program. These relationships have contributed to carp and international conference presentations, erection of educational signage, community meetings, carp musters, factsheets, electrofishing demonstrations, school and university presentations, production of nutrient rich fertiliser and numerous departmental reports.