A new fish-tagging system was developed by scientists from Richland's Pacific Northwest National Laboratory to study young salmon. They found that the behavior of the young fish seem contrary to earlier theories.

PNNL ecologist Geoff McMichael and his colleagues worked in a span of more than 10 years to complete the new fish-tagging system called the Juvenile Salmon Acoustic Telemetry System. It is very advanced that is was able to gather an immense amount of important data on young salmon behavior.

The researchers concentrated on monitoring fish as they go downstream towards the vast ocean. They tagged 8,000 migrant fish with battery-operated transmitters before releasing them into the ocean from 140-245 miles upstream. Receivers and detectors were spread out close to the floor of the ocean, in intervals of 1.5 miles.

The miniscule transmitters, which is less than a centimeter thick, gives off high-pitched bleeps several seconds at a time, which then produce sound ripples that could be received and distinguished by the receivers among the various oceanic sounds.

Their salmon-monitoring set up successfully detected 1,701 fish which swam in the proximity of 100 square miles north or south of the ocean. According to McMichael, majority of the fish swim to the north of the ocean but they could not confirm how far they went in other directions before swimming north.

Previous methods of fish-tagging used cheaper and smaller integrated transponders. It needs the fish to swim closer to the detectors, requiring more to be receivers to be laid on the ocean floor.

McMichael explained that their interest in the young salmon's first few weeks in the ocean is very important because it tells much of the fish survival and mortality. He wrote, "Much of their health and the success of their later runs upstream to start the next generation are dictated by those first few weeks in the ocean."

The study was published in the Dec. 2 issue of Animal Biotelemetry.