National Wetlands Update September 2012
Issue No. 21, September 2012
Optimising environmental watering of wetlands to benefit native fish
Leah Beesley, Alison King and John Koehn, Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment, Victoria; Amina Price, Ben Gawne and Daryl Nielsen, Murray-Darling Freshwater Research Centre, CSIRO Land & Water and La Trobe University
Pumping environmental water into a wetland in
the lower Murray River. (Leah Beesley)
The Murray-Darling Basin (MDB) supports more than 30 000 wetlands, including sites of international importance. Many of these wetlands have suffered significant degradation as a consequence of altered hydrology associated with river regulation. Wetlands in the southern portion of the MDB suffered further stress during the Millennium drought (2002-2009).
During the drought, managers used small parcels of environmental water to improve wetland health. While delivering water has obvious benefits for trees, benefits to native fish are less clear. Fish response will depend on when, how and where the water is delivered. For example, if wetlands are watered during winter when fish do not spawn, then watering may do little for a spawning response.
A recent study sought to provide information on how to get the best fish response from environmental watering by asking whether attributes of watering or wetland habitat have the greatest influence on fish response. The project was funded by the Australian Government's Raising National Water Standards program, under the water-dependent ecosystems theme aimed at achieving more effective and efficient management of environmental water.
We examined how fish responded to watering by studying 27 watering events in wetlands of the Murray River. We found that attributes of watering were more important than the wetland habitat attributes. Fish recruitment and abundance in the short and medium term after watering was greatest when watering was relatively natural (sourced from the main river channel, or a large permanent channel, and delivered through a regulated or unregulated channel). Conversely, fish recruitment and abundance was lowest when watering was highly artificial (water sourced from an irrigation channel and passed through small pipes or fish un-friendly culverts).
This implies that management initiatives aimed at improving the use of floodplain wetlands by native fish should initially focus on delivering water at appropriate times and recreating 'as-natural-as-possible' wetland-river connectivity by removing impediments to fish passage. The recruitment of individual fish species in the short term was greatest when wetlands were watered during their peak spawning period.
We stress that benefits to fish in wetlands will do little to benefit the fish meta community and the river system in general, unless they can return to the river. Very little is known about the effects of environmental water at such broad spatiotemporal scales, and this needs to be addressed.
A wetland in the Murray Irrigation District
after receiving environmental water. (Leah Beesley)
Wetland habitat thriving after the delivery
of environmental water. (Leah Beesley)
For further information, including products to assist in making decisions on water regimes that will benefit native fish populations see Watering floodplain wetlands in the Murray-Darling Basin for native fish.