Lend me your (fish) ears

By / 5th of June, 2014
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AN important key to managing the world’s fish stocks could lie with a pile of very small bones in South Australia.

In a prime example of how science informs policy, researchers from the South Australian Research and Development Institute (SARDI) are assessing not just the level of fish stocks off the coast, but also how they got to be there.

Chemical analysis of ear bones, or otoliths, can provide details of a fish’s movements over a lifetime, in much the same way as a tree’s rings tell the story of its growth.

Chemical analysis of ear bones, or otoliths, can provide details of a fish’s movements over a lifetime, in much the same way as a tree’s rings tell the story of its growth.

The distinctive natures of different bodies of water can leave distinct signals in the otoliths.

It’s not everyday work, because it is both complex and expensive, but it is a good investment if it helps provide important clues to present and future stock structures.

“For us the primary motivation is a significant change we are seeing in South Australian waters,” said SARDI’s Marine Scalefish research leader Dr Anthony Fowler.

“Spencer Gulf has long been our main fishing area but lately returns have been pretty poor, while St Vincent’s Gulf has really taken off.

“This is a major ecological phenomenon and we want to know whether it’s a coincidence, or whether the fish are actually moving from one gulf to the other.”

The project has been under way since 2011 and data analysis is expected to be completed later this year. The answers it provides will help determine whether fish stocks need to be managed at a local, regional or even wider level.

Previous work by SARDI has informed state government decisions to close or limit fishing activities to protect fish stocks and spawning grounds.

Dr Fowler said ear bones also provided more easily accessible information about a fish’s age, and this had allowed scientists to develop the first detailed picture of the growth history of snapper, some of which had been shown to live for up to 36 years.

He and his colleagues have been collecting ear bones from an Adelaide fish market every week for the past 14 years. They now have an “otolith bank” including around 30,000 snapper, garfish and King George whiting.

“Understanding fish stocks is very complex,” he said. “Fish are a moving feast living in a three-dimensional environment, and that is why it is difficult to understand their movement patterns which then determine their stock structure.”

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Key contacts

Dr Anthony Fowler Subprogram Leader Finfish Fisheries
61 8 8207 5432 anthony.fowler@sa.gov.au