Bulletin

Issue: July 2005

Research in Action

Tracking the energy needs of Southern Bluefin Tuna

A team from La Trobe University’s Department of Zoology believes it has overcome the problem that has plagued devices used to record the bodily activities of animals.

It has developed the ‘iLogR’, a tiny ultra-smart thumbnail sized data logger that for the first time allows scientists to track the metabolic rate of active free ranging wild animals.

Working with the Head of La Trobe Zoology, Dr Peter Frappell, top left, and researcher Mr Tim Clark, right, the Department’s electronic engineer, Mr Brian Taylor, has developed the first miniature tag that does not use electro-cardiograph (ECG) technology.

As part of a $1.6 million research project aimed at increasing the production of Southern Bluefin Tuna, the La Trobe team developed the 20x20x10 mm iLogR. For fish or any other free ranging wild animal it will give readings of heart rate, body temperature, depth and other activity every minute for an entire year.

Previous devices designed to provide such real time information have been plagued with problems because ECG technology relies on picking up and transmitting information using electrical impulses.

This is fine when the animal is at rest or moving slowly, but when a very muscular animal, like a full-grown 200 kg two metre-long Southern Bluefin Tuna swims rapidly, the electrical impulses from its intense muscle activity blots out the ECG signal.

‘ILogR detects heart rate by using non-electrical signals as opposed to electrical signals – and is hardly affected by muscle activity,’ Mr Taylor says.

Constant muscle activity is the essence of the Southern Bluefin Tuna’s well-being. They must keep moving at least their body length every second to ensure a water flow over their gills, and their body shape and heart muscles have evolved to ensure the high speed needed to catch their prey.

Juvenile tuna are netted in the wild in the Southern Ocean, transferred to cages and towed slowly to Port Lincoln, South Australia, where they are raised in massive cages submerged in the sea.

Early trials of iLogR at La Trobe’s Melbourne campus at Bundoora on Murray Cod make the scientists confident that it will be effective when used in Southern Bluefin Tuna.

The La Trobe team is working with colleagues at the University of Adelaide and the South Australian Research and Development Institute (SARDI) to increase the productivity of the Southern Bluefin Tuna industry. Mr Clark has just completed a PhD in Zoology at La Trobe and started as a postdoctoral fellow at the University of Adelaide.

The industry is worth $350 million a year with most fish going to the Japanese ‘Sashimi’ market.

There are quotas on the numbers of fish that can be taken so any further expansion of the industry must come from more efficient growth of the quota-limited fish supply.

There have been recent developments including new kinds of food for the tuna, but there is still much work to be done collecting information on metabolic physiology to enable more efficient practices such as larger cage carrying capacities, more efficient feeding strategies and pollution control.

Collecting data including heart rate, body temperature, depth and other activity, and predicting the energy requirements of the fish at any given moment, will help the industry develop such strategies.

The La Trobe and Adelaide teams will use the first iLogRs on several caged Southern Bluefin Tuna at Port Lincoln in July and hope to deploy at least 100 at the start of the main tuna raising season next January.

Dr Frappell says to predict the energy requirements of tuna during different activities such as feeding and swimming requires establishing a relationship between the tuna’s heart rate and rate of oxygen uptake which is a measure of metabolic rate. This will be achieved in conjunction with their Adelaide colleagues by using the iLogRs on tuna housed in a large, specially designed floating enclosure at Port Lincoln in which the tuna’s oxygen uptake can be measured at the same time as heart rate.

He says that fitting the device takes less than five minutes, researchers are in the process of reducing that time, and several overseas universities have already expressed interest in the device as it can be used in a wide range of conservation studies. •

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