About the document
Pouched lamprey (Geotria australis) and short-headed lamprey (Mordacia mordax) are the only anadromous fishes native to the Murray–Darling Basin (MDB). Historically, lamprey were common in the River Murray with spawning migrations potentially extending up to 2,000 km upstream, but they are now rarely encountered, suggesting barriers to migration and flow regulation have impacted these species. In the past decade, however, a focus on restoring connectivity (e.g. fishway construction) and ecologically relevant components of flow regimes, through the delivery of environmental water, have increased opportunities for migration that may aid recovery of lamprey in the MDB. A key objective of the delivery of Commonwealth environmental water in the southern MDB is to improve end-of-system flow and connectivity through the Murray Barrages and Murray Mouth to support fish movement and expanded distributions. The migratory life histories of pouched lamprey and short-headed lamprey make these species well suited to demonstrate the achievement of these outcomes.
The objective of the project was to assess the abundance of adult lamprey at the Murray Barrages in 2019, and to use passive integrated transponder (PIT) telemetry to investigate subsequent upstream spawning migrations in the MDB.
The project found that in winter–spring 2019, releases of Commonwealth environmental water from the Murray Barrages facilitated connectivity between freshwater, estuarine and marine environments, and subsequently resulted in beneficial migration outcomes for lamprey. This included high abundances (relative to preceding years) of both pouched (45) and short-headed (16) lamprey passing the Murray Barrages, and ultimately, migrations that continued for 100’s of kilometres upstream.
Data collected in this and allied monitoring projects may be used to inform future environmental water delivery and infrastructure management in the southern MDB. This includes:
- Greatest abundances of migrating pouched lamprey occurred during years of moderate winter–spring barrage discharge (mean daily discharge ≥2,500 ML.d-1) with short periods of peak discharge of ~15,000 ML.d-1. Thus, the hydrographs delivered in 2015, 2017 and 2019 likely represent appropriate templates for future environmental water planning.
- Importantly, each of these years comprised multi-site watering events and were supported by return flows from delivery of Commonwealth environmental water in the Goulburn River. The delivery of Commonwealth environmental water is critical to maintaining barrage discharge and connectivity during years of low flow; and
- Lamprey primarily pass upstream via fishways on Goolwa, Mundoo and Tauwitchere barrages. Abundances tend to be greater at the Goolwa and Mundoo fishways, likely due to their proximity to the Murray Mouth and greater influence of discharge from these barrages/fishways on downstream salinities. As such, during times of limited water availability, winter–spring releases that specifically target lamprey migration could be prioritised to Goolwa and Mundoo barrages to maximise attraction.