News Archive

Is the world's largest fish getting smaller?

It's a controversial question and a difficult one to answer, but Dr Mark Meekan of the Australian Institute of Marine Science (AIMS) believes that the average size of whale sharks congregating at Ningaloo has indeed been dropping.

Dr Meekan addressed the issue at a public talk in August, as part of a series presented by the Oceans Institute and AIMS to celebrate the International Year of Biodiversity.

Data from satellite tracking and photographs suggest that the biggest whale sharks have been disappearing from Ningaloo since the 1990s. Dr Meekan believes that shipping collisions are at least partly responsible, and there are a few reasons why giant whale sharks are the most vulnerable.

"The larger you are, the more likely you are to get in the way of a ship, and the longer you'll take to get out of the way," says Dr Meekan. "You're also more likely, over time, to encounter a ship."

Poaching is another problem, as the whale shark fishing industry still exists in some parts of south-east Asia. Their remarkably soft flesh lends them the nickname ‘tofu fish', and a single individual can fetch up to $200,000.

One of the key messages of Dr Meekan's talk was that small-scale ecotourism in countries like Indonesia will be critical for securing the whale shark's future by "developing alternative livelihoods for traditional fisherman."

The public lecture series - designed to broadly address the current state of our oceans - also featured talks by Winthrop Professors Gary Kendrick and Malcolm McCulloch.

W/Prof. Kendrick illustrated the remarkable diversity and endemism of Australian marine life, with a specific focus on seaweeds and seagrasses. Seagrasses differ from seaweeds in that they evolved from land plants which recolonised the ocean.

Both are seriously threatened by climate change and eutrophication, amongst other things. W/Prof. Kendrick argued that their future survival depends on their ability to adapt quickly, and the way that the threats will compound and interact with one another.

W/Prof. Malcolm McCulloch addressed the topic of coral reefs, posing the question: "Will they survive climate change?"

On a global scale, coral reefs are confronted by sea level rise, ocean acidification, and coral bleaching. Locally, reefs are threatened by agricultural runoff, over-harvesting, and introduced marine pests.

As with seaweeds and seagrasses, the question of whether coral reefs will survive depends on the combined effect of global and local stressors, and the ability of corals to adapt and migrate.

Page 12: The UWA Oceans Institute December Newsletter

Media references

Maryann Evetts (The UWA Oceans Institute), (+61 8) 6488 8116