Title

delwp.vic.gov.au

Background

River Blackfish (Gadopsis marmoratus), also known as

Greasys, Slimys and Marbled Cod, are a medium sized

freshwater fish, native to south-eastern Australia. While

River Blackfish live in a range of habitats, adults prefer

pools and woody structures. They typically have a small

home range of about 25-30m, although some fish will

move over 100m. They breed in spring and summer,

when water temperatures are about 14-20°C. Females

lay large, adhesive eggs in hollow logs and cavities of

rocks. Relatively few eggs are laid (generally between

30 – 500 eggs) and larger females produce more eggs.

River Blackfish are a popular angling species and were

historically widespread and abundant, including in west

Gippsland. Leongatha, in the Tarwin River Catchment,

was once one of the best River Blackfish locations in

Victoria. Now, there are fewer in the Tarwin River

catchment and their distribution is patchy (they’re more

often found in upper tributaries). Local anglers note

their catches have steadily declined in recent decades.

Over the last 25 years, West Gippsland Catchment

Management Authority have been working with

landholders and community groups to improve the

health of the Tarwin River catchment and habitat for

River Blackfish and other fish species. Actions include

removing weeds, planting native trees, fencing,

stabilising riverbanks and installing fishways. Since

River Blackfish don’t tend to migrate, and breed locally,

they haven’t however naturally recolonised rehabilitated

areas. Translocating fish into rehabilitated areas may

therefore be a valuable way to support recolonisation

and population recovery in the Tarwin River and other

waterways throughout the species’ range.

Project Objectives

A pilot project commenced in 2015 to:

• translocate River Blackfish into rehabilitated

reaches within their former range in the Tarwin

River catchment.

• assess whether fish remain in the translocated

areas.

• assess if recruitment occurs.

Approach

Twenty-seven adult River Blackfish were collected from

upland areas of the Tarwin River west branch using

backpack electrofishing in October 2015. Fish were

translocated into rehabilitated reaches of Coalition

Creek, a tributary further downstream, where they

previously occurred. To monitor whether River Blackfish

stayed at the translocation sites, fish were tagged with

acoustic transmitters and acoustic receivers were

placed at about 90m intervals along the translocated

reach and at the junction of the Coalition Creek and

Tarwin River. Electrofishing and fyke netting surveys

were subsequently carried out in autumn 2016, 2017

and 2018 to also monitor for fish survival, establishment

of new home ranges, and recruitment.

Fig 1: A River Blackfish ready for release (Photo: ARI)

Translocation of River Blackfish – Tarwin River

pilot study

Project Overview

Translocation of River Blackfish – Tarwin River

pilot study

Results

Acoustic monitoring over the first eight months showed

that twenty-two of the translocated River Blackfish

survived and remained within the translocated reaches.

Five River Blackfish were not recorded after being

translocated. These fish may have not moved past a

receiver, rejected their tags, died or their tags failed.

Of the River Blackfish that were tracked, most fish

moved less than 100m, with two fish moving more than

1km. When stream flows increased, some fish moved

more frequently or over larger distances. One fish even

moved over 1.6 km – the longest distance recorded for

River Blackfish!

A few adult fish and no young fish were collected during

the electrofishing and fyke netting surveys in autumn

2016, while no adult or young fish were collected in

2017 and 2018, suggesting that the River Blackfish

failed to establish permanent, new home ranges and

reproduce. Factors which may explain results include:

• Adult fish stayed in the translocation reaches and

recruited, but adult and juvenile fish have not

been detected in surveys.

• The effect of stress related to translocation close

to the species’ spawning period, resulted in fish

not breeding.

• Not enough fish were translocated to obtain a

viable breeding population.

• Adult fish moved from the site when conditions

become unfavourable.

A severe drought in Coalition Creek about six months

after translocation resulted in the creek ceasing to flow,

with subsequent decreased dissolved oxygen and

increased water temperature. This poor water quality

may have caused translocated fish to leave the

reaches, and reiterates the need to carefully select

translocation sites with good instream and riparian

habitat in catchments not impacted by potential water

quality issues.

Key findings and next steps

This pilot study indicates that River Blackfish can be

translocated and will remain in translocated areas for at

least eight months. Translocation may represent one

tool that can contribute to restoration of River Blackfish

within their former range. Future remediation

approaches should consider using a larger number of

translocated fish and more suitable rehabilitation areas

that are resilient to drought. It would also be worthwhile

investigating the feasibility of a captive breeding and

stocking program for River Blackfish in Victoria.

A Partnership

This work was funded through the Recreational Fishing

Grants Program. West Gippsland CMA managed the

project, ARI undertook the fish research and monitoring,

and the Leongatha Angling Club contributed to site

selection and project support.

Contact

Justin.O’Connor@delwp.vic.gov.au

References

O’Connor, J., Amtstaetter, F., Ayres, R., Koster, W. and

Bowler, M (2016) Translocation of River Blackfish – Tarwin

River pilot study. An unpublished client report for West

Gippsland Catchment Management Authority. ARI

Fig 2: Acoustic receivers placed instream (Photo: ARI)

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visit http://creativecommons.org/licenses/by/4.0/

ISBN 978-1-76077-105-8 (print), 978-1-76077-106-5 (pdf/online)

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