"Where the river meets the sea": fish behaviour in Australian estuaries
New South Wales, Australia
Nicholas Payne, Iain Suthers, Matt Taylor
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Estuarine environments face regular extremes in temperature, salt levels and turbidity, yet support flourishing aquatic life. How does this dynamic environment affect animal behaviour?
Project Background
Estuaries are dynamic environments. They are characterised by strong tides and often-heavy fluctuations in salinity, temperature and turbidity. They are also home to diverse assemblages of fish, many of which are prime targets for recreational and commercial fishers.
For this project, we are using a variety of electronic tagging technology to understand the behavioral mechanisms that help fish persist in dynamic estuarine habitats along the New South Wales coastline.
So far we have collected a suite of fascinating data from:
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yellowfin bream (Acanthopagrus australis),
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mulloway (Argyrosomus japonicus),
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dusky flathead (Platycephalus fuscus),
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sand whiting (Sillago ciliata) and
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several stingrays (Dasyatis fluviorum and Trygonoptera testacea).
We have a particular focus on addressing the roles of rainfall and temperature in driving behavior of these animals, and early signs suggest these factors have a big influence on the day-to-day life of estuarine fish. Our hope is that this information will provide a better understanding of how environmental variation contributes to the structuring of estuarine ecosystems.
Project Updates
Rain 'flips' activity in estuarine yellowfin bream
30th May 2014
Activity tags deployed in yellowfin bream Acanthopagrus australis near Sydney led to a remarkable discovery: these bream are diurnally active during normal conditions, but repeatedly switch to nocturnal activity in the days following heavy rain. Rhythm switches like this are rather uncommon in nature, but are a great example of the adaptations required to persist in estuaries. More details can be in the full paper found here.
Not too hot, not too cold: optimum temperatures for flathead activity
19th June 2014
Dusky flathead Platycephalus fuscus inhabit estuaries throughout winter and summer from southern Victoria all the way up to northern Queensland, and therefore experience a large range of water temperatures. Accelerometry tags deployed in wild flathead near Sydney revealed that they are most active when the water is around 23°C, and much less active during both cooler and warmer temperatures. Interestingly, the temperatures that are so cold and hot that they don’t move at all in Sydney are similar to the minimum winter temperature and maximum summer temperature at the southern and northern (respectively) limits of their range. This suggests temperature may play a large role in limiting the geographical range of flathead. More details can be found in the full paper here.
Quiet week? Boating activity reduces foraging intensity of mulloway
25th December 2014
Mulloway Argyrosomus japonicus are an economically important fish species in Australia, and a common target of recreational fishermen in estuaries throughout NSW. By measuring activity levels of mulloway in an estuary south of Sydney via accelerometers, we found that these fish are less active on weekends than during the week. This interesting finding was supported by stomach content analyses, which showed that mulloway consume less than half the amount of food on weekends than they do on weekdays. Boating activity is far higher on weekends than weekdays throughout most of Australia, and mulloway have long been considered sensitive to the sound of boat engines. This study in as example of the various ways that human activity can impact fish populations – it’s not just about over-fishing, habitat degradation and climate change! More details can be found in the full paper here