FISHING: Penstock Lagoon ecology in the spotlight

In late January 2025 the Anglers Alliance Tasmania (AAT) set up an intensive workshop at Penstock Lagoon to help discuss and assess the ecological health of our Central Highlands trout fisheries.

The workshop was attended by several AAT members, representatives from the Inland Fisheries Service and scientists from the University of Tasmania, Latrobe University and CSIRO.

The aim of the workshop was to discuss plans to build on the previous work undertaken by AAT members in regard to mayfly population changes in our shallow inland waters and to determine a further plan of action also with key input from the angling community.

There was broad agreement within the group that further research is required to understand more on what’s potentially impacting on ecosystem health (including mayflies and other key indicator species) across several important Central Highland fisheries.

The AAT did a study at Penstock Lagoon and the key findings in the decline of Mayfly numbers worldwide have been pinpointed to climate change, habitat degradation, pollution and other ecological stressors.

Mayflies are recognised worldwide as indicators of environmental health and as an insect family they have a low tolerance to poor water quality.

Studies were done at Penstock Lagoon to establish baseline data on the presence of insects of concern which were mainly mayflies and macroinvertebrate diversity in general.

The sampling and tests showed that mayfly nymph populations were well below those seen there in the past.

Water and sediment sampling tests carried out by Hydro Tasmania ruled out pollution issues.

A drone was used which then relayed back pictures that showed extensive damage from boats where the canal enters the lagoon.

Having already ruled out pollution as a major impact the drone footage brought attention to habitat degradation from boats and their motors.

Boats impact aquatic plants either directly, through contact with the propeller and boat hull or indirectly through turbidity and wave damage.

Propellers can chop off plant shoots and uproot whole plants when operated in shallow water.

Increased turbidity from boat activity limits the light available for plants and it also limits where plants can also grow.

Add the fact that the lagoon has had an increase in angler activity and this has also made an impact as well.

Recent data backs up observations in relation to increased boat traffic and angling pressure compared to earlier years associated with better mayfly fishing.

Similarly, the ever-increasing size of boats seen on Penstock backed up by bigger motor capacity therefore increases the depth of disturbance, creating further concern on the likely impact of boat-based fishing.

Saying that studies show that Penstock Lagoon is still performing well although with some minor adjustments to fish stocking, the taking of larger fish and reducing angling effort it's said this will provide better outcomes.

In addition, the goals for brown and rainbow trout need to be reviewed and set at more realistic levels.

Predatory implications of trout also mentioned in overseas studies are a major ecological stressor for the mayfly’s decline.

Based on the number of trout in the lagoon, even a conservative estimate of the number of nymphs they eat suggests a very large effect on mayfly hatches.

Poor performance of other fisheries has meant more anglers have visited Penstock Lagoon and Historic IFS data shows some connection between stocking and angler visitation as the IFS seeks to address the increased “harvesting” of fish from increased angler effort.

This increase in visitation is compounded as the publishing of stocking information encourages increased angler efforts and “harvesting” and so on.

From Hydro water level data, seasonal variation indicates periods of high stress levels for both trout and Mayflies, in what for much of the year is a closed system as evaporation and loss outweigh any inflow.

With climate change adding to the uncertainty of rainfall and increasing evaporation, the continuation of the current practice of allowing summer water flow from the Shannon River will become even more important.

In addition, the lower water levels are likely to produce greater damage to the lagoon bed as water depth decreases allowing boat motors and hulls to reach the bottom.

Resultant turbidity from boats in shallower water will increase the effects of wind turbulence which is also greater in shallow water.

Hydro data indicates turbidity on Penstock Lagoon is a large factor due to wind speed, however research on turbidity shows its importance in macrophyte habitat and macroinvertebrate respiration.

Increased turbidity reduces the depth to which light can penetrate and restricts plant capacity to photosynthesise and silt settlement can also smother aquatic plants.

Turbidity and silt also impact mayfly nymphs in reducing the materials upon which they graze, and it also smothers their gills as well.

This information was largely taken from the interim report and studies on Penstock Lagoon Published by the IFS.

Planning is underway to determine the next steps which include the exploration of research funding opportunities to progress and expand on the initial work by AAT members.

TASMANIAN ANGLING HALL OF FAME NOMINATIONS

The Anglers Alliance of Tasmania is calling for nominations for the Tasmanian Angling Hall of Fame 2025.

Membership of the Angling Hall of Fame is the pinnacle of achievement for an individual's contribution towards the betterment of freshwater angling in Tasmania.

The achievement represents the highest level of peer recognition within freshwater fishing and nominations must adhere to the guidelines and selection criteria detailed in this link: https://www.anglersalliance.org.au/about-the-hall-of-fame 

Nominations need to be submitted by Friday 25 April 2025 by email to Tim Munro, Executive Officer, Anglers Alliance Tasmania@anglersalliance@gmail.com

NEW INLAND FISHERIES HEAD

Dr Ryan Wilkinson has been appointed as the new Director of Inland Fisheries Service after taking on the acting Directors role in March 2024.

Ryan said: “It has been a privilege to work as a member of the IFS team over the past ‘almost’ 12 months.

A highlight has been engaging with individual anglers, angling club members, representatives of Anglers Alliance Tasmania (AAT) and Trout Guides and Lodges Tasmania (TGALT), and members of the Inland Fisheries Advisory Council (IFAC), who are all deeply passionate about the status and future of our inland fishery.

“I look forward to continuing this engagement and working hard on behalf of all anglers to help develop our fishery into the future.”

Ryan is a passionate recreational angler who has a PhD in fish biology from Flinders University and moved to Tasmania in 2006 to take on an academic position at the University of Tasmania specialising in fish health, physiology and reproductive biology.

He maintained a balanced portfolio of teaching and research over six years at the University and supervised several honours and PhD students.

Since leaving the University he has had a range of roles in the commercial aquaculture sector.

He also worked for Biosecurity Tasmania for 5 years - initially as the Industry Collaboration Manager and most recently as Director of Biosecurity Operations, managing a busy operational team of more than 100 staff across the state.

Tip Of The Week - When planning a fishing trip always take more clothing with you than you think you'll need. If the weather does change then you'll still keep warm and be able to keep fishing.

Send in your fishing reports, pics and tips to valleyfishes@gmail.com and go to TasmanianCountry.com every Wednesday for the latest fishing news, tips and hot spots.

Tight Lines until next week.