Exploring ecosystems takes plenty of guts

Sydney Morning Herald
By Nicky Phillips
June 7, 2012

At the headquarters of the Secretariat of the Pacific Community in Noumea, Elodie Vourey pulls the stomach of a bigeye tuna from a large plastic bag and puts it on a white tray.

With tweezers in one hand and a scalpel in the other, the laboratory assistant carves a deep incision into the fleshy organ, revealing the fish’s last meal. Inside, a few partially digested fish are mixed with squid and other morsels too mangled to identify without a microscope.

The stomach is one of more than 7000 Vourey and her supervisor, Valerie Allain, have extracted from marine creatures, including sharks, dolphin fish and tuna, then examined, catalogued and frozen. The extensive gut collection forms the basis of Allain’s decade-long project to better understand the ecosystem that houses the region’s $6 billion-a-year tuna industry.

”If you’ve got a healthy ecosystem, you’ve got healthy tuna stocks,” says Allain, who collects fish that are too damaged to be tagged by the SPC or specimens that have been collected by boat observers.

To measure the state of an ecosystem, scientists must understand how species interact, which generally boils down to who eats whom.

The research by Allain and others has shown a fish’s biggest predator is not the fisherman but its peers. ”The number of fish eaten by other fish is three times higher than all the fish we catch,” says Allain, a senior fisheries research scientist.

She has also shown that near-shore reef fish make up a significant proportion of a tuna’s diet. While predation by other fish is part of a balanced ecosystem, overfishing can tip that balance, she says.

The data Allain collects feeds a mathematical model that tests how the ecosystem and tuna stocks react to changes in fishing intensity, as well as weather patterns such as El Nino and La Nina, and global warming.

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