September 23, 2014


This is Fish Radio. I’m Laine Welch — Its back to the drawing board for halibut iTags. More after this –


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A project that uses Smart Phone technology to track halibut is being retweaked. The internal tags, which are the first to test geomagnetism to track fish migrations, were implanted in 30 halibut over two years ago. The iTags record magnetic field strength on three axes and have accelerometers and pitch and roll detectors. But it turns out, magnets were the tags undoing.


The early version of the tags we deployed in 2011 had some metal components inside that were actually picking up magnetic charges and maintaining those charges and screwing up the calibrations by the time we got them back there was no way to really track the fish.


Tim Loher is the tag team project leader with the International Pacific Halibut Commission.


  It’s complex. In short, you’ve got an electronic tag that you’re trying to detect magnetism, and magnetism and electricity are pretty much the same sort of thing. So it’s difficult to develop a tag that doesn’t interfere with itself. It’s really easy to do when you’ve got a magnetometer that’s the size of a suitcase but when you try to miniaturize it down into a tag, it take some time.


The problem has been fixed, Loher says, and a new version will be tested next month at Glacier Bay.  The geomagnetic tags can record data every 30 seconds for seven years. They give real-time positions on halibut, and track them without any need for light, acoustics or GPS satellites.


They demonstrate that we can track fish within 50 miles or so, and from a management perspective is the kind of resolution that will work great for us. We can tell when fish are moving among regulatory areas and when they are migrating on or offshore, and that is exactly the kind of stuff we are looking to get eventually.


Loher says it’s likely to be a few more years before the iTags are deployed on 1,000 or more fish from Oregon to Attu. He says it will provide more information on halibut travels than ever before.


  The depth information tells us when fish are moving on or offshore, but with geomagnetism we can track fish among regulatory areas and for fish that are moving downstream as they age we can track their progress as they go from their nursery areas toward their adult feeding and breeding grounds. It’s going to be a really powerful experiment.


Returned iTagged halibut are worth $500 to fishermen. Fish with external darts or wire tags pay out at $100 or $200 along the Aleutians.   The IPHC wants to know where the halibut was caught, and would love to get the ear bones to age the fish. Find links at

Fish Radio is also brought to you by Ocean Beauty Seafoods – who  salutes and says thanks to  the men and women fishing across Alaska for their hard work and dedication.  In Kodiak, I’m Laine Welch.