Scientists Prove Nemo Does Come Home

A team of Australian, American and French coral reef scientists have established that Nemo-the lovable orange, black and white clownfish of movie fame-really does come home. Around 60 percent of clownfish return to their home reef after being swept into the open ocean as babies.

Working on pristine coral reefs in a marine protected area in Papua New Guinea, an international team-led by Dr. Geoff Jones and Dr. GlennAlmany of the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University-has pioneered a new way to study fish populations by tagging adult fish with a minute trace of a harmless isotope, which they then pass on to their offspring.

The tag is enabling the researchers to understand the degree to which young fish return to their home area or go off to interbreed with more distant populations.

This helps to build a picture of the extent to which fish populations are connected or isolated from one another-currently a vital missing link in the sustainable management of fish stocks.

"If we can understand how fish larvae disperse, it will enable better design of marine protected areas and this will help in the rebuilding of threatened fish populations," Almany explained.

In trials at Kimbe Bay, Papua New Guinea, researchers tagged over 300 female clownfish and vagabond butterflyfish with a barium isotope. Females pass the isotope to their offspring and it lodges in their offspring’s ear-bones.

"The isotope is stable, non-radioactive and quite harmless to the fish in these minute amounts, or to humans if it were to be used to tag a table fish," Almany explained. "It’s simply a way of telling one group offish of the same species from another."

The team later returned to confirm the tags had worked and studies how many of the offspring went back to their home reef or had dispersed to other reefs. They found around 60 percent of the juvenile fish returned to the home reef-a tiny dot in the ocean only 300 meters across-after being carried out to sea as babies.

Copyright Compass Publications, Inc. Jun 2007