Snowy Lakes Food Web

There has been recent concerns over a decrease in the size and number of  rainbow trout in the Snowy Lakes. Food limitations and competition between rainbow and brown trout have been suggested as a potential cause.

DPI electrofishing monitoring has also  identified fluctuations in rainbow trout sizes during the spawn run over the past decade, with smaller sized fish recorded between 2016-2019.

1. Are the edges of Lake Jindabyne the dominant foraging/ feeding area for all salmonid size classes?

2. Does the food energy derived from tributaries feeding Lake Jindabyne (Snowy River, Little Thredbo River and Sawpit Creek) contribute to salmonid biomass in the lake?

3. Does foraging area and food web/energy pathway differ between species?

Understanding the source and flow of energy (food sources) in an ecosystem, provides valuable information on ecological processes and for fisheries management. To better understand food webs in Lake Jindabyne we examined gut contents and undertook stable isotope analysis.

Stable isotope analysis is based on the principle ‘you are what you eat.' This method most frequently uses the isotopes of carbon (14C) and nitrogen (15N) to trace the flow of nutrients through food webs and assess trophic levels.

The current study assessed the major energy pathways/ food webs supporting brown trout, rainbow trout and Atlantic salmon in Lake Jindabyne and its tributaries. This study was completed in collaboration with the University of Canberra.

Total sample size for the study was 92 brown trout, 62 rainbow trout and 7 Atlantic salmon. 161 total salmonids.

The gut analysis of brown and rainbow trout, as well as Atlantic salmon were used during this study.

During the Snowy Mountains Trout Festival in 2018, gut and flesh samples were donated at the Jindabyne weigh in station.

Some of the sample locations from Lake Jindabyne.

In Lake Jindabyne the dominant feeding habitat for salmonid species of all sampled size classes and species, were the lake edges.

However, there was some evidence that suggested rainbow trout were relying on the open water energy pathway (e.g. feeding in open water). The results for rainbow trout also suggested there was some linkage between the diets in the Snowy River and Lake Jindabyne.

Small goldfish and shrimp (pictured above and below) were sampled in high abundance around the edges of Lake Jindabyne in 2020 and possibly form an integral part of the food web.

Daphnia (a small pelagic crustacean) is also likely to be important for the diet of rainbow trout and these can now be monitored during hydroacoustic surveys

Stable isotope analysis typically indicates energy pathways/ food sources over a matter of months rather than the lifetime of the organism. Therefore, a more detail study is required to fully understand how these patterns vary between lakes and within and between years.

Nevertheless this information will be combined with population modelling studies in 2022 to better understand the trout fisheries in the Snowy Lakes.

Follow the link below for more information on freshwater fishery research.

We would like to thank the University of Canberra and Max Mallett for collaborating on this work.