ILWS - Charles Sturt University
ILWS - Charles Sturt University

Native and invasive fish dispersal, spawning and trophic dynamics during a managed river-floodplain connection.  (2018-2019)

Investigators/researchers

Dr Keller Kopf, Associate Professor Skye Wassens, and Luke McPhan

Funding

CEWO, $236,787

Research Theme

Environmental Water

Description

Floodplains are critical habitats for native fish.  They provide highly productive nursery habitat and food to support reproduction and recruitment.  For this project, researchers are evaluating how a managed connection of the Murrumbidgee river with its floodplain influences the food resources available to native and invasive fish.

Since the diet of fish is reflected in isotope and fatty acid concentrations of their tissues, they are using these analyses to identify the food resources supporting fish reproduction, growth and recruitment.

Researchers began monitoring the effects of an environmental water delivery in September 2018, across the floodplain to Tala and Yanga Lakes on the lower Murrumbidgee River.  The environmental water delivery was aimed at supporting native fish and waterbirds in the floodplain system. The lakes are also home to other native fauna including freshwater shrimp, frogs, snakes and turtles.

The area had had less than 80 mm of rain since January 2018 and Yanga National Park was one of a few sites selected to receive Commonwealth water for the environment in 2018. During the drought period, it was identified as a priority site that needed protection, to build resilience so that native fish and other wildlife can recover when the dry conditions ease.

Starting in 2018, tissue samples were collected from a range of fish species around the Murray-Darling and analyses of nitrogen and carbon isotopes were used to estimate the trophic position of the fish community. This one year project served as a pilot study to test the feasibility and utility of using a trophic position indicator as a tool for annual monitoring of long-term ecosystem changes in the Murray-Darling.

Key findings of this monitoring included:

  • Golden perch spawning and recruitment most likely occurred from within the floodplain system rather than movement from the river system as indicated by stable isotope analyses and catch data.
  • Successful floodplain spawning and recruitment of golden perch was detected in Tala Creek and the hatch-dates of recruits over-lapped with environmental water delivery.
  • The diet of common carp and recruit stages of golden perch overlapped, suggesting that the two species are in competition for food resources provided by floodplain inundation.
  • Waterbird abundance increased a month after water for the environment connected to each of the lakes, Tala and Yanga.
  • Piscivorous (fish eating) birds were the most abundant functional group of waterbirds at both Tala and Yanga Lakes in all survey months, with Australian pelicans being the most abundant.
  • Waterbird abundance was the second highest since 2010 based on annual spring counts conducted by NSW Department of Planning, Industry and Environment.

Outputs

Kopf R.K., Wassens S., McPhan L., Dyer J., Maguire J., Spencer J., Amos C., Kopf S., Whiterod N. (2019) Native and invasive fish dispersal, spawning and trophic dynamics during a managed riverfloodplain connection. Commonwealth Environmental Water Office. Murrumbidgee Selected Area Final report, pp 1-49.

Outcomes

The project’s findings will be used in adaptive management actions to guide the timing and magnitude of environmental water delivery connections between river channels and floodplain ecosystems.

Contact

Dr R. Keller Kopf
email 

March 2020