Signals from the Atlantic salmon highway( For years scientists have struggled ...)

For years scientists have struggled to understand the decline and slow recovery of Atlantic salmon, a once abundant and highly prized game and food fish native to New England rivers. Biologists agree that poor marine survival is affecting salmon in the U.S. and Canada, but specific causes are difficult to determine in the ocean. Small acoustic tags and associated technology may provide some answers.

Thirty of 150 Atlantic salmon smolts tagged by NOAA's Northeast Fisheries Science Center (NEFSC) in Maine's Penobscot River and released in Brewer, Maine in mid-May have crossed a line of underwater receivers off Halifax, Nova Scotia, the first fish to be tracked using the new global Ocean Tracking Network. The concept is similar to an EZ pass for highway toll booths, but for fish.

"The tracking system is deployed and working, which is great news," said John Kocik, who is leading the tagging project with colleague James Hawkes at the NEFSC's Maine Field Station in Orono, Maine. "We started ultrasonic tagging programs in Maine in 1997 and have learned much about salmon ecology in the estuaries and bays of the Gulf of Maine," Kocik said. "Our team is really excited that fish from our most recent work in the Penobscot River have been detected so far along on their migration northward. The first data provided valuable information about how long it took Atlantic salmon from the Penobscot River to reach Halifax."

The acoustic transmitters or tags, which are about the size of the silver eraser holder on a pencil, were surgically implanted in May in salmon smolts that were each six to seven inches in length. The surgeries, done at the Eddington Salmon Club, take less than seven minutes. After a brief recovery, the smolts were released at the nearby Brewer Boat Ramp.

Each tag has a unique identification code that transmits an ultrasonic signal every few seconds. To detect these tags locally, NEFSC maintains a network of more than 80 aco
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