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Fish in a blender?

By David Wood

Now you may think (like I did when I first arrived in the science world) that fish and pumps would not mix. A pump is affectively a giant blender and a fish (if it was unlucky enough to be sucked up) would not exit the pump in any form resembling a living fish. How wrong I was.

One of the lovely places I get to call my office on occasion is the Hattah Lakes system, part of the Hattah-Kulkyne National Park in north-western Victoria. It is comprised of around 18 lakes (12 of which are RAMSAR listed) nestled among the sand dunes. Chalka Creek feeds these lakes from the Murray River, but only during elevated flows.

Hattah Lake 

Murray River with the entrance to Chalka Creek on the left

During the millennium drought flows in the Murray River were too low to flood into Chalka Creek. Consequently the lakes became dry and the once majestic River Red Gums bordering the water courses of this system were looking a little worse for wear. This resulted in management authorities deciding to pump environmental water from the Murray River into Chalka Creek and the lakes from 2005.

The Hattah Lakes were pumped numerous times over the next 5 years with the intention of keeping these trees alive and maintaining the ‘ecological character’ of the area. We, at the Murray–Darling Freshwater Research Centre (MDFRC), have undertaken monitoring work at these lakes since 2005, and this has included fish surveys.

Following pumping of environmental water from the Murray River into the bone dry Hattah Lakes, a diverse native fish community developed. The lakes were allowed to dry naturally (sadly resulting in the whole fish community perishing; there was no link back to the Murray River) and subsequent additions of environmental water led to the emergence of a similar fish community suggesting that the first time occurrence had not just been a chance event.

Pump 

Temporary pump setup at Hattah on the Murray River (2010).

Notice that in the last paragraph I specified ‘native’ fish community? The community was indeed almost completely comprised of native species. Eastern gambusia, renowned for invading just about any pool of water, was not found in the Hattah Lakes following these pumping events. Also the number of Carp during this period appeared to be limited to only a handful which became apparent as the lake had dried to a small, shallow pool. Therefore we concluded that the pumps were somehow ‘filtering’ the fish community, though it was unclear if this was due to timing, depth, distance of abstraction pipe from bank, type of pump or any number of other factors.

In the summer of 2010–11, flooding in the Murray River caused Hattah Lakes to fill naturally for the first time in 10 years. As a result we found Spangled perch, which is as far south as had ever been recorded (see Iain ‘Listy’ Ellis spiel on Spangs) and Oriental weatherloach (which was previously recorded only as far west as Euston; ≈100km upstream). In the years following, fish catch in the Hattah Lakes were dominated by Carp and Eastern gambusia, proving that these species were more than happy to hang out in the Hattah Lakes once free access was granted.

Around the time of the flood, approval was granted to undertake the installation of a number of block banks and regulators around Hattah and the mother of all pumping stations (think 1000 ML.day-1) on the Murray River enabling artificial flooding of vast, long-dry, areas of the floodplain. Construction was completed last year and after the first pumping event took place some interesting fish results surfaced. However we will save that story for another time (and storyteller).

As I have only been at MDFRC for 5 years, after some quick math you might realise I was not on the scene during the initial pumping during the drought. This little piece would not have been possible without the hard work and slogging though much mud of the girls and guys that collected fish data from the Hattah Lakes in the years gone by. Also to the science nerds whom cottoned onto the fact that very few exotic species inhabited the lakes following pumping.

For more information see:

Vilizzi L, McCarthy BJ, Scholz O, Sharpe CP, Wood DB (2013) Managed and natural inundation: benefits for conservation of native fish in a semi-arid wetland system. Aquatic Conservation: Marine and Freshwater Ecosystems 23, 37-50.

Fykes

Small and Large fyke nets set at Hattah Lakes (Lake Lockie).


Carp_and Dave Wood

David Wood studied biology at Deakin University in Geelong, and moved to Mildura to work at the Murray-Darling Freshwater Research Centre about 5 years ago. He is a sport junkie.