Key causes of fish kills
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The author roughly 40 years ago with one of the new polymer spool Alvey reels and a Butterworth MT7144 surf rod. Those white spotted guitarfish are surprisingly good tucker.
Supporting local manufacturing * from P70
Ignoring the fact that we found the school and others came along only after seeing our bent rods, maybe the fact that we were catching more fish than him should have been a hint that perhaps his logic was flawed. Once warm-water fish stocking kicked off, the unique fisheries it created saw a vacuum in the design of imported lures suitable for our native species. Enter Aussie ingenuity and a host of backyard lure makers began turning out timber diving lures, catering specifically to Australian fish in local scenarios. A select few of those early pioneers went on to become mainstays of the freshwater scene and are still thriving today – Predatek (formerly Downunder Lures) and Oar-Gee Lures come to mind. www.bnbfishing.com.au
Sadly, many of the most innovative designers of the era are no longer with us or have stopped making lures for the mainstream market. Wandering around the workshop in my Mongrel boots sees a couple of Dawn Tools vices, a large Robbo’s bandsaw, plenty of old Stanley woodworking tools and boxes of Sidchrome spanners, all still Aussie made. I’m old enough to have owned Australian-made whitegoods, televisions, a Mixmaster and sewing machines, all of which are very hard to find now. Why buy Australian made? Quite simply, to invest in jobs for our grandkids. Buying cheap imports when locally manufactured products are available still will see more manufacturing going the way of our automotive industry.
ISH kills are defined as a sudden mass mortality of wild fish. Fish kills can occur at any time, though data indicates fish kills are more likely to occur in summer or following sudden changes in temperature. Some of the key causes of fish kills are outlined in the information below. Blackwater Blackwater occurs naturally over time when leaf litter and woody debris build up on the floodplain and then get washed into the river system during a flood. It’s an important part of the aquatic food web, as it provides food for insects, which feed fish, frogs and other aquatic wildlife. When there is a prolonged dry period, the leaf litter and organic matter on the floodplain builds up until the next flood event. This can result in a significant amount of organic matter returning to the river with any big flushes of water after prolonged drought, making blackwater events more likely. Hypoxic blackwater When there is a lot of organic material washed into the river, its rapid decay can consume dissolved oxygen from the water. If dissolved oxygen drops to very low levels, this can cause ‘hypoxic’ water, which can be stressful for native fish and can lead to fish kills. Bushfires Bushfires can also influence water quality and cause conditions similar to blackwater events. After a bushfire, rain can carry ash and burnt material into waterways.
The cover offered by plants and trees is lost, meaning the soil is more easily eroded and can be washed into rivers. This can contribute to unpredictable changes to the water chemistry, including to blackwater events. More information on blackwater can be found on the MDBA website, mdba.gov. au/climate-and-riverhealth/water-quality/ blackwater, and in the ‘About blackwater’ factsheet from DPIE Environment, Energy and Science, environment. nsw.gov.au/-/media / OEH/Corporate-Site/ Documents/Water/Wa ter-for-the-environment/ about-blackwater-factsheet-200209.pdf To notify the department of potential blackwater events, email waterqualitydata@dpie. nsw.gov.au or to report a fish kill, contact the Fishers Watch Phoneline on 1800 043 536. Stratification Stratification is when the surface of the water heats up more than the deeper water. That warmer layer tends to be warm and well-oxygenated compared to the deeper water that is colder and oxygen-depleted. Thermal stratification Blue green algal bloom • Algal flourish in warm and still conditions, particularly in the absence of high flow. Surface water layer • Warm high nutrient
load from run off • Dissolved oxygen by day, depletion overnight • Limited fish habitat. Deep water layer • Cooler low light penetration • Low dissolved oxygen (hypoxia) • Poor fish habitat. Decomposition of organic matter • Depletes dissolved oxygen. De-stratification (‘Turn over’) Sudden weather events or small increases in flow can mix the warmer surface water and cooler deep water – essentially breaking down the temperature stratification. These changes can mix the warmer surface water with cooler deep water. Algal blooms may also be disrupted, potentially increasing decomposition, and further depleting oxygen. This means that even at the surface, dissolved oxygen levels can become critical, killing fish. Simple things you can do Be on the lookout for any changes in water quality – that includes changes to the colour or odour of your local waterway – and report them to the Fishers Watch Phoneline on 1800 043 536. And call the phoneline if you observe any dead fish or fish starting to gasp at the water surfaces.
Fish kills are defined as a sudden mass mortality of wild fish. Bush ’n Beach Fishing, May 2024 – Page 71
