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Stomach contents unlock secret to tuna lifestyle

16 May, 2012, NSJ

The smell in Dr Valerie Allain’s laboratory can get quite strong at times, especially when she and her two assistants are defrosting another batch of tuna stomachs.

Two thousand frozen stomachs are stacked up in her freezer at the Secretariat of the Pacific Community (SPC) in Noumea, all waiting their turn to be analysed.[frax09alpha]

The results have demonstrated the important connection between coastal areas and the open ocean which mutually benefit from each other.

Tunafish stomach content reveals a wealth of information for oceanic food web science

Dr Allain discovered that reef organisms drifting in the open ocean play an important part in the diet of larger fish.  The stomachs collected on the tuna fishing vessels contained many small fish and crustaceans, nearly 6% of the diet of yellowfin tuna.

“This is the first time anyone has been able to demonstrate the importance of reef species in oceanic food webs at such a large geographic scale,” she says.

“An army marches on its stomach, but fish depend on a food chain which stretches from the tiniest organism to the shark.”

“By inspecting the contents of the stomachs of tuna and other large fish predators, I can tell what they have been eating and any changes in their diet.  The more we know about tuna – what they eat and who eat them – the better we can manage the whole fishery.”

The western Pacific contains an estimated 1.5 million tonnes of yellowfin tuna, and Dr Allain has shown they eat nearly 800,000 tonnes of reef prey every year.

The results of Dr Allain’s work are published in the international journal PLoS ONE today.

Analysing what tuna eat is another part of the complex process of tracking the tuna fishery in the Pacific carried out by SPC. It is a $US6 billion per year industry, of enormous importance to the 26 Pacific Island Countries and Territories (PICTS).

Dr Allain works closely with the independent observers carried on the tuna fishing vessels, who count and measure the fish.  Their role is to identify the species and the location of the catch, and log any by-catch as well as collecting stomachs, gonads and other specimens required by scientists.

Her results are based on a close examination of the contents of 8000 tuna stomachs, over a ten-year period.

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