River Blackfish (Gadopsos marmoratus) have declined throughout south-east Australia, possibly because of reduced habitat condition. In west Gippsland, while historically found throughout the freshwater reaches of the Tarwin River catchment, they are now found only in the upper reaches. The decline of this popular recreational fishing species has occurred despite the West Gippsland Catchment Management Authority (WGCMA), local landholders and community members, undertaking extensive waterway rehabilitation activities in these areas over the last 25 years. It is thought that certain characteristics of River Blackfish, such as its non-migratory nature, localised breeding strategy and small home range may be limiting natural recolonisation of these rehabilitated areas. Thus, further approaches to increase numbers and range of this species requires investigation.
Since 2015, the WGCMA, ARI and local recreational fishers have worked together to trial the translocation of River Blackfish into rehabilitated habitat sites in the Tarwin River and investigate whether they establish new home ranges. Twenty-seven adult fish were collected from source locations in the Tarwin River and moved to rehabilitated and non-rehabilitated reaches downstream within the species' historical distribution. Fish were implanted with acoustic tags, and a series of acoustic receivers were placed along the river to monitor their movements over the short term. Twenty-two of the translocated River Blackfish survived and remained within the translocated areas for the majority of their tag's battery life. The other five fish were not recorded again.
Electrofishing surveys in autumn 2017 and 2018 did not collect any translocated fish and it is believed the fish may have left the site. A severe drought in the study area about six months following the translocation resulted in the creek ceasing to flow, leading to poor water quality (decreased dissolved oxygen levels and increased water temperature). This emphasised the need to carefully select potential translocation sites that have good instream and riparian habitat which are not impacted by potential water quality issues.
This pilot project has provided valuable insights regarding translocations of River Blackfish to enable successful recolonisation of former habitats. Monitoring of the River Blackfish in the Tarwin River is continuing, including their breeding and recruitment success. Recommendations have also been developed regarding further translocations and other approaches that can contribute to the conservation of this species. This project is a collaboration with WGCMA, funded by the Victorian Government using Recreational Fishing Licence Fees.
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The following fact sheet provides more detail about the project: