FISH FACTOR: Study takes aim at magnetic fields, salmon returns
Is it a coincidence that one of the world’s largest mineral deposits is located near the world’s largest sockeye salmon spawning grounds at Bristol Bay? And if the likes of a Pebble mine removed the bulk of those deep deposits that also create the world’s magnetic field, could it disrupt the salmon’s ability to find their way home?
A study, funded by Arron Kallenberg of Homer, founder/CEO of Wild Alaskan Company and a third generation Bristol Bay fisherman, aims to find out.
“It’s not even been 10 years since we’ve discovered that salmon, sea turtles and other marine species are using the Earth’s magnetic field as a way to know where they are and to make important navigation decisions. But what is the magnetic environment that they need to thrive, and what might humans be doing that might keep them from thriving,” said Dr. Nathan Putman, a senior scientist at Texas-based LGL Ecological Research Associates and an expert on animals’ use of magnetics fields in migration who is leading the study.
“The salmon at Bristol Bay are tuned into thousands of years of experience,” Putman said. “Might removing magnetic minerals alter the magnetic landscape they have experienced, and to what extent?”
The combinations of magnetic field strength and angles give the salmon a sense of where they are, he explained.
“For instance, if a fish has left its river and finds itself in a stronger magnetic field than when it departed, it’s got a good chance of being further north of the river. And if it finds itself in a weaker magnetic field, it has a good chance of being further south. It can use that information to decide which way it should go, depending on whether it’s heading out to its foraging grounds, or if it’s matured and it’s time to head back home.”
Putman’s earlier studies on pinks revealed that salmon have multi-purpose navigational tools.
“The handy thing about the magnetic field is that it’s both a compass and a map. A compass by itself only gives you a direction. The Earth’s magnetic field gives you that direction, but for salmon it also gives a sense of where in the Bering Sea or the Gulf of Alaska they are. It’s sort of part compass, part GPS,” he explained.
Putman said it is easy to manipulate magnetic environments in the lab.
“We call them magnetic displacement experiments,” he said. “And they perform quite well. The salmon seem to know how to orient their movements when they grow up in a pristine magnetic rearing environment. But if you add something as simple as a nearby iron pipe, it distorts the field. Then you have the same family of fish, the same setup, the same sort of behavioral assays and they don’t appear capable of using the magnetic field to make navigation decisions.”
For the Bristol Bay project Putman is using a high-resolution magnetic model for 304,000 latitude/longitude points over the past 20 years, looking at the impact of mining activity on fluctuations in local geomagnetic fields. By comparing the rate of change in the geomagnetic field near mining sites to baseline background variability, he can identify potential man-made impacts of mineral extraction on field variations.
“I think it really does put some burden back on us as humans to ask how we are altering the magnetic environment around salmon, whether it’s from mineral extraction or electric cables running across or through streams. How might we be presenting salmon or other species with challenges from how we’re manipulating their habitats. That’s where we’re going with this project.”
Putman’s results should be known by this summer when the sockeye run is returning to Bristol Bay.
Want to know where most fishermen live in Alaska? Or where most Alaska fishing boats are home ported?
United Fishermen of Alaska has just released its updated Fishing Facts for every region of Alaska, plus the West Coast. The facts are updated through 2018, the most complete year available.
At a glance, they show that nearly 8,700 permit holders fished in 2018, or which 6,055 were Alaska residents. More than 21,341 crew licenses were purchased, split almost evenly between residents and non-residents.
Alaska’s seafood industry employed nearly 59,000 direct jobs, more than any other private sector. More than $172 million in fishing taxes were collected, of which $73 million went to state coffers and $51 million to local governments.
Homer is home to 615 fishing boats and nearly 20 percent of its population fishes, earning $69 million at the docks in 2018.
A total of 636 vessels call Kodiak Island home with 1,074 resident fishermen, or 17.3 percent of the population, who earned $105 million. Kodiak lays claim to 15 processing facilities, from ‘mom and pops’ to majors.
At Petersburg, nearly 24 percent of the population fishes for a living on 620 home-ported boats. Their income was pegged at $50.5 million.
Only nine permit holders fished out of Dutch Harbor/Unalaska but its 8 big processing plants helped generate $8.2 million in fishery taxes, both to the region and the state.
Just more than 6,000 Washington residents plus crew fished in Alaska in 2018. Of the total harvest of 5.7 billion pounds, 4 billion pounds was taken by Washington residents. Of the dockside value of $1.94 billion, Washingtonians pocketed $900 million.
The Fishing Facts include regional fishing, processing jobs and wages, fishery tax revenues and legislative districts.
Halibut catch limits for 2021 will be revealed on Jan. 29, the last day of the International Pacific Halibut Meetings that will convene virtually starting on Jan. 25.
A preliminary review of the 2020 fishery shows a total catch for the U.S. and British Columbia at 35.7 million pounds, down 11 percent from 2019.
Sixty-three percent was taken in commercial fisheries (22.3 million pounds). Alaska fishermen took nearly 16 million pounds, 7 percent below the catch limit.
Recreational fisheries took 17 percent (6 million pounds); 3 percent went to both subsistence and surveys/research (one million pounds each).
More than 5 million pounds of halibut was taken as bycatch in other fisheries.
Homer got the biggest chunk of the Pacific halibut landings at 18 percent (3 million pounds), followed by Dutch Harbor and Kodiak. Juneau at 1.3 million pounds narrowly outpaced Sitka for total commercial halibut landings.