Paramount Importance

Monitoring fish communities and water quality is one of the ways we can assess the health of a river or estuary.

When there has been little or no flow, the water can stop mixing and become stratified. This means layers form in the water column, with lighter surface water sitting above denser, saltier bottom water. Once this happens, oxygen from the surface may not reach the bottom. At the same time, organic matter, algae and plant material can settle and break down, with microbes using up oxygen in the process. Over time, the bottom waters can become deoxygenated, or even anoxic, meaning there is little to no oxygen available.

This can also affect the sediment, because organic material accumulates on the bottom and oxygen is rapidly used up as it decomposes. When the sediment becomes deoxygenated, it can reduce habitat quality for bottom-dwelling animals and influence the release of nutrients and other compounds back into the water.
By monitoring water quality and fish communities, we can better understand how the system is responding to low flow, stratification and changing environmental conditions.

This project is funded by the Australian Government Natural Heritage Trust and delivered by PHCC, a member of the Commonwealth Regional Delivery Partners panel.

All sampling is conducted under permit.

Presenter:

Estuaries are not uniform habitats. As freshwater from rivers mixes with seawater from the ocean, salinity changes across space and time, creating different zones for different fish species.

Some species remain closer to the river where salinity is lower, others dominate near the mouth where marine influence is strongest, and many move between these areas as conditions change. This partitioning reduces competition and allows estuaries to support a diverse mix of freshwater, estuarine, and marine fishes within the same system.

In this way, salinity gradients help structure fish communities, influencing where species live, feed, reproduce, and seek refuge. That is part of what makes estuaries so ecologically important: they are dynamic transition zones where fish assemblages are shaped by the constant interaction between land, river, and sea.

All fishing is under permit

Presenter:

Monitoring the health of the ecosystem by looking at the fish communities.
The nearshore waters were sampled using a 21.5 m seine net that was walked out to a maximum depth of 1.5 m, deployed parallel to the shore, and dragged towards and onto the shore or boat.

Bigger fish can swim faster than we pull the net so we generally catch small and juvenile fish. Fish respond very quickly to different environmental conditions and can give an assessment of the condition of the estuary. This has been subjected to extensive testing and validation over several years and shown to be a robust tool for understanding the ecological health responses to local-scale disturbances and the recovery of the estuary following their removal.

This project is funded by the Australian Government Natural Heritage Trust and delivered by PHCC, a member of the Commonwealth Regional Delivery Partners panel.
All fishing is under permit

Presenter: