Environmental Water for Thomson’s Native Fish

Environmental water from the Thomson Reservoir is timed this spring to provide conditions for the migration of important native and threatened fish species including Australian grayling.

The spring fresh (environmental flow) will contribute to a controlled increase in streamflow in the Thomson River, with the peak spanning a four day period beginning Friday 30 October to Monday 2 November 2015.

An autumn fresh in April successfully triggered the migration of adult Australian grayling downstream to spawn and the spring fresh will provide conditions for the resulting juveniles to migrate back upstream.

West Gippsland Catchment Management Authority CEO, Martin Fuller, said this sequence of releases is very important to the life cycle of the Australian grayling, a nationally significant species listed as vulnerable.

“The autumn fresh released earlier in the year triggered the largest spawning response from Australian grayling we have recorded in the Thomson system, with thousands of eggs deposited in their spawning habitat.”

“These eggs have dispersed into the Gippsland Lakes and adjoining marine habitat and the young are now waiting for a freshwater pulse that will allow them to migrate upstream into one of the adjoining rivers. With this spring fresh we hope to trigger this upstream migration and recruit juvenile grayling into the Thomson system,” explained Mr Fuller.

“With such a strong spawning response this year, this spring fresh is really important to complete this life cycle for Australian grayling and support their self-sustaining population in the Thomson.”

The flows are important for other significant migratory species such as Australian bass, estuary perch and tupong that also depend on these flow conditions for improvements in-stream habitat quality and opportunities for migration.

The spring fresh will also improve in-stream habitat and seed dispersal for high value native vegetation by transporting seeds down the system to enable germination elsewhere in the catchment.

“Releases are being made within the river channel limits and well below minor flood levels, ensuring the environmental water release does not inundate private land,” added Mr Fuller.

Flows of up to 800ML/day can be expected in the Thomson River from 30 October to 2 November. During this time, indicative river heights are up to 0.6 m. This applies to the sections of the Thomson River immediately downstream of Thomson Dam.

Due to system complexities, localised changes in water levels are difficult to predict so all reasonable care should be taken when undertaking activities associated with the river at these times.

The Victorian Environmental Water Holder prioritised this water release as part of its Seasonal Watering Plan 2015-16, which aims to improve river and wetland health across the State. The plan can be accessed at www.vewh.vic.gov.au.

For further information on this environmental water release please call the West Gippsland Catchment Management Authority on 1300 094 262.

Thomson River at Walhalla Rd Bridge during October 2014 water release