It’s back to the drawing board for halibut iTags that will soon tell us more about where the fish travels than ever before.
The internal tags, which were deployed in 30 halibut two years ago, were the first to test Smart Phone geomagnetic advances to track the migrations of fish. The tags record magnetic field strength on three axes and have accelerometers and pitch and roll detectors, explained Tim Loher, a biologist with the International Pacific Halibut Commission.
“Without being able to tell whether or not your tag is horizontal, you can’t really get the axis of the magnetism. The invention of the iPhone pointed the way to make the pitch and roll detectors small enough to put in fish tags,” he said.
The geomagnetic tags, which can record data every 30 seconds for seven years, are designed to give real time, daily positions on halibut and track them without any need for light, acoustics or communication with GPS satellites – all the information will be onboard when the fishermen catch them.
But in the field tests, magnetism was the gut tags’ undoing.
“The tags had some metal components inside them that were actually picking up magnetic charges and screwing up the calibrations,” Loher said.
He added that a new metal-free version of the tags already has been developed, and will be deployed in Glacier Bay halibut later this summer by project associate Julie Nielsen, a graduate student at UAF/Juneau. Within a couple of years, the IPHC team plans to tag 1,000 or more halibut from Oregon to Attu.
“We’ve got a lot of migration issues and we are trying to set our quotas and determine exactly how to assess the stock,” Loher said. “We know the halibut are moving but we are having trouble getting refined estimates of movement by size, age and regulatory area, so hopefully this will help nail that down. It’s going to be a really powerful experiment.”
The IPHC will pay a $500 reward for the return of any geomagnetic tags (which are accompanied by external wire tags). Rewards ranging from $50-$200 also are paid for returns of halibut containing darts or wire tags.
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