Monitoring and research
Our understanding of fish movement requirements has developed over the years as new information is discovered through monitoring what fish do and researching the reasons why.
Without any information on the swimming abilities of native Australian fish, early Australian fishways were based on overseas models used in Europe or America. Unfortunately, those designs catered for species such as salmon and trout that are excellent swimmers. As time progressed, observations at these fishways showed that our Australian native fish were actually pretty poor swimmers in comparison to their northern hemisphere counterparts and the fishways weren't helping native fish to move around much at all. More suitable fishway designs were needed, and these were informed by research into how native fish moved, and whether certain conditions such as water velocity, depth, and turbulence helped or hindered their movement.
Field observations and laboratory experiments have similarly improved our understanding of good and bad road crossing design, determined how weirs and floodgates limit access to important habitats, and how changes to their management can reduce their impact.
Most recently, the importance of connectivity within and between rivers, has been confirmed through applications of electronic tagging and tracking, use of natural markers in the ear bones of fish, and genetics - highlighting the importance of using new techniques as they become available.
Tagging fish
Knowing where fish can and can't move provides valuable insight into what sites are acting to block fish passage. Knowing when fish need to undertake movements provides an understanding of their seasonal requirements and an improved understanding of how water management in a river or catchment may affect these movements.
Tagging fish allows researchers to see where a fish has travelled from and the direction they are moving. There are several types of tags that can be used to identify fish including external tags, Passive Integrated Transponders (PIT), radio, acoustic and satellite tags.
External tags allow fish to be recognised based on the colour of the tag and an associated unique number. These tags are used to identify fish when they are caught by fishers, in nets or when electrofishing. They provide a snapshot view of the fish's life - a point when the fish was tagged, followed by point(s) when the fish is recaptured.
Passive Integrated Transponders (PIT) are tags that are inserted into the body of the fish and are not externally visible. These tags sit inactive in the fish until it passes a nearby underwater antenna or reader that communicates with the tag to obtain a unique identifier and record its presence. These tags and readers are often used in fishways to determine if a fish has passed into and through the fishway successfully.
Battery powered tags include radio, acoustic and satellite tags and are attached internally or externally to the fish depending on the species and application. The tags typically have a limited life (months to years) due to their internal battery but, unlike passively activated PIT tags, have a large detection range. Acoustic tags are used in conjunction with a series of submerged receivers that are strategically placed along a river or water body in an "array" to track the behaviour of tagged fish. When a fish passes a receiver, a signal from the tag is detected with the tag’s unique identifier and a detection time is recorded. With an array set up, directional fish movements and actions such as responses to environmental cues can be determined. Further information on different tag types and their applications can be found in this scientific article.
The animation in the banner of this page is showing the results of an acoustic tagging study of fish within the Wakool and Yallakool river system. These rivers are part of an anabranch system of the Murray River in NSW. The coloured lines following the river lines are fish movements - each fish having a different colour. Fish move up to barriers in the river, then downstream and back again. The lines in the small panel on the left of the banner show river flows. Fish movements past barriers can be seen when flows reach certain level and the barrier becomes submerged. This type of monitoring clearly shows how impactful barriers can be on fish movement, reducing their ability to migrate until river flows drown out barriers.
Another animation and presentation explainer by DPIRD Fisheries’ scientist Jason Thiem can be found on the Australian Government’s Department of Climate Change, Energy, the Environment and Water webpage. This presentation shows where Golden Perch moved within the lower Darling / Baaka River below the Menindee Lakes from December 2021 - May 2022. Juvenile Golden Perch were fitted with acoustic tracking tags to monitor their movements. River flows were found to strongly influence the direction and speed of fish movement. Fish moved in upstream and downstream directions, with some fish moving slowly, and others moving rapidly in the Baaka. One fish even journeyed into the Murray River and was last recorded at Lock 7 near the junction of Rufus River, 653 km downstream!
Using water chemistry
Recently the importance of connectivity between rivers has been further confirmed by using stable isotopes naturally present in the water and absorbed into fish.
Fish ear bones, called otoliths, can be used like natural passports to track where fish have been and how they move between different water bodies. These tiny structures grow in layers over a fish’s lifetime, absorbing chemicals from the surrounding water. Scientists can analyse these chemical signatures to determine whether a fish has spent time in freshwater, saltwater, or even different rivers.
For example, fish that migrate between the ocean and rivers (such as mullet or barramundi) pick up distinct chemical markers from the saltwater and freshwater environments, helping researchers confirm these movements. Even for fish that stay entirely in freshwater, variations in water chemistry between rivers allow scientists to trace their migration pathways. In some cases, this has revealed incredible journeys, such as a species of catfish in the Amazon that travels over 8,000 km in its lifetime!
Closer to home, within the Murray-Darling Basin, individual catchments have distinct water chemistry1. By analysing the chemical composition of a fish’s earbone at the first year of growth, scientists can tell where the fish was born and analysis of subsequent growth rings can inform if and where the fish has moved to over time2.
Using this technique to better understand Golden Perch movements3, scientists identified that when fish were up to two years old, they either remained in the same location, moved upstream or moved downstream, away from where they were born. Linking this information to growth of the fish, scientists determined that fish who moved away from where they were born showed greater growth than those fish who remained "resident".
This has implications on growth rates for fish that can't move due to the presence of barriers to fish passage and highlights the importance of using new techniques as they become available.
References
1. Barrow, J.S., Morrongiello, J.R., Koehn, J.D., Zampatti, B., Fanson, B., Thiem, J.D., Tonkin, Z., Koster, W.M., Butler, G.L., Strawbridge, A., Brooks, S.G., Woods, R. and Yen, J.D.L. (2024) Dispersal direction, geographic location and river discharge all influence juvenile growth of a freshwater fish. Freshwater Biology, 00: 1 - 11.
2. Thiem, J.D., Baumgartner, L.J., Fanson, B., Sadekov, A., Tonkin, Z., and Zampatti, B.(2022) Contrasting natal origin and movement history informs recovery pathways for three lowland river species following a mass fish kill. Marine and Freshwater Research, 73: 237 - 246.
3. Barrow, J.S., Yen, J.D.L., Koehn, J.D., Zampatti, B., Fanson, B., Thiem, J.D., Tonkin, Z., Strawbridge, A., and Morrongiello, J.R. (2021) Lifetime movement history is associated with variable growth of a potamodromous freshwater fish. Journal of Animal Ecology, 90: 2560 - 2572.
