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Fish Factor: Magnetism proves to be halibut tags' undoing

June 21st 5:44 pm | Laine Welch Print this article   Email this article   Create a Shortlink for this article

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.

HYPERLINK "http://www.iphc.washington.edu" www.iphc.washington.edu

Profiler payouts

Water column profilers that provide ocean data are still sitting on the ocean floor and scientists hope to get them back. The profilers, purchased by the IPHC with a half million dollar grant from NOAA Fisheries, were deployed four years ago at more than 1,200 halibut survey stations between Oregon and the Bering Sea. They measure salinity, temperature, pH, dissolved oxygen and chlorophyll content, and the data is shared with many users.

One profiler was lost off the east side of Kodiak; another disappeared on the south side of Adak. The 60 pound profilers are housed in a steel cage and could be snagged on the bottom or detected with depth sounders.

"Particularly the one that is off Kodiak Island," said Bruce Leaman, IPHC executive director. "It doesn't have the floats on top but it's sitting on hard bottom and you would get a little bit of a bump in there. The one that is off Adak Island, you can actually see the floats on your echo sounder if you're going by."

The IPHC will pay a $1,500 reward for the return of the profilers.

"We hope the money is incentive enough so people will actually go looking for them," Leaman said. "It's a small thing in a large area but we have some fairly precise location information and we would dearly like to get them back because they

have important data, plus they are reusable and are durable pieces of equipment."

Daily salmon tracker

You can now track Alaska salmon catches by region and species on a daily basis with ADF&G's popular Blue Sheet. Starting this season, salmon managers made the change from weekly to daily catch updates from mid-May through September.

A glance at the Blue Sheet through Monday showed that the total salmon catch had topped two million fish, most coming from the Copper River/Prince William Sound region; the remainder from the westward region.

Along with the daily blue sheet, ADF&G also provides a weekly in-season summary that graphs the progression of commercial salmon harvests and compares it with the five year averages.

More cod coming

The global cod glut is likely to continue into 2014 as quotas are expected to increase again in Norway, Russia and Iceland. Market expert John Sackton said the Barents Sea cod catch could increase to 993,000 metric tons. That is seen as a peak, based on the age structure of the stock, but when declines begin in 2015 they are not expected to be significant, Sackton said.

Iceland has announced another increase in its cod quota to 215,000 tons next year, up 10 percent. Researchers said Iceland's cod spawning stock is the largest since the early 1960s.

In Alaska, Pacific cod accounts for 11 percent of total fish landings. Harvest levels from the Bering Sea and Gulf of Alaska were set at about 320,000 tons this year and are not expected to change much in 2014.

Unlike Alaska crab or wild salmon, cod has no special brand and is lumped in as a "whitefish" commodity. A portion of the Alaska cod pack goes to US markets as fillets, but most

goes to China for reprocessing.

Visit Laine Welch's Web site at www.alaskafishradio.com.

 

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