Swimming with the big fish, studying the small

Imagine trying to track in the open seas the migration of fishes that are only a few millimetres to a centimetre long.

By Rebecca Hancock

Imagine trying to track in the open seas the migration of fishes that are only a few millimetres to a centimetre long, almost transparent and bearing little resemblance to their adult forms.

The challenges of studying larval fish

It's a challenge that Dr Jeff Leis and his research team† have met over the years by donning their diving gear and following larval fishes through the water, painstakingly observing them with the naked eye. It is an essential part of Jeff's research to understand how and how far the fishes of the Great Barrier Reef disperse in the first weeks to months of their lives, during their 'pelagic larval stage'.

Larval fish don't just drift

Previous research by Dr Leis has shown that rather than being weak swimmers at the mercy of ocean currents, larval fishes can swim faster than currents and they know where they are going. They are able to hear the 'sound' of the coral reefs, and use this ability to navigate. They may even take cues from the angle of the sun.

Testing new technology

Now, thanks to a new drifting observational device, known as DISC (for Drifting In Situ Chamber), designed by colleague Dr Claire Paris from the University of Miami, the task of tracking larval fish has become a lot easier. DISC is fitted with a camera, and photographs are taken at regular intervals enabling the orientation of the larvae to be detected and quantified while naturally influenced by factors in the open ocean (such as salinity, temperature and current). The apparatus also makes it possible to study smaller and younger larvae than before.

In recent months, Drs Leis and Paris have been testing the DISC and gathering new data on the behaviour of Damselfish larvae at the Australian Museum's Lizard Island Research Station in the northern part of the Great Barrier Reef.

Improved marine planning

'The DISC, as well as other means of studying larval-fish behaviour help us better understand just what influences the dispersal of larval fish and how far they will travel before they settle on a final reef home,' said Dr Leis.

'This research will provide new inputs to biophysical larval dispersal models to make them more accurate. The modelling results will in turn be used to help identify marine areas that need to be protected so that fish populations can survive and thrive,' Dr Leis added.

Drs Leis and Paris plan to present the results of their findings at the Indo-Pacific Fish Conference conference in Perth this June.

* Jeff's research team includes current Museum staff Michelle Yerman, Amanda Hay, Brooke Carson-Ewart and Matt Lockett, and collaborators from several other Australian and overseas institutions.

Acknowledgment of Support

This research is supported by the Hermon Slade Foundation and the Marine and Tropical Sciences Research Facility. Dr Paris received an Australian Museum Visiting Research Fellowship.