sockeye salmon spawning in a river
sockeye salmon spawning in a river

How a Mineral Mine Could Disrupt Salmon Migration for Generations

January 25th, 2021

A Q & A With Dr. Nathan F. Putnam

Wild Alaskan Company is funding new research to examine the relationship between mineral deposits, magnetic fields, and how wild salmon navigate the world — including how they return to their natal waters, sometimes traveling thousands of miles, in order to spawn and complete their life-cycle.

The new research comes as developers of the proposed Pebble Mine, one of the largest mineral deposits in the world, have committed themselves to not taking any step that would impact the delicate life-cycle of local salmon. Pebble Mine is located in Bristol Bay, which happens to be home to the largest sockeye salmon spawning ground on the planet. 

Led by Dr. Nathan F. Putnam, this study will specifically investigate the relationship between magnetically disruptive human activities — such as mining — and the successful migration of wild salmon. Dr. Putnam is one of North America’s leading experts on how animals use magnetic fields for migratory navigation, particularly marine species that swim long distances.

Wild Alaskan Company chatted with Dr. Putnam to learn why this research project may be critical to protecting the health of salmon populations, and how its findings may help us to better understand the complex migration habits of wild salmon and other animals who rely on magnetic cues to navigate the globe.

Just to summarize, this study is designed around the idea that juvenile salmon have magnetic cues imprinted on them before they go to sea, where magnetic information is critical to their migration. 

Yes, that’s one of the important premises here. Although the salmon are using magnetic information in the open ocean, it’s linked back to where they grow, where they rear, where they develop. That’s probably an important calibration point for them that sets the stage for how they perceive the magnetic information later in life. 

If magnetic material — like a mineral deposit — is removed or disturbed from their natal waters during their life cycle, this could disturb their migration patterns?

It depends on the magnitude. There are a lot of open questions in terms of the sensory biology of salmon [and their migration patterns] — what cues they’re using, how they weight different cues, whether those are visual or auditory or olfactory or magnetic. 

It’s only been in some ways relatively recent that we have gotten definitive evidence that salmon are quite sensitive to magnetic fields, and sufficiently sensitive to them that it appears that they can use Earth’s magnetic field as a kind of map, sort of like a GPS that tells them where they are. 

So how does something like the proposed Pebble Mine relate to animals' use of magnetic maps?

When you’re mining, you’re extracting an awful lot of material from the ground. And a lot of that material might be magnetic; in fact, that’s why we’re so keen on, as humans, mapping out magnetic anomalies and things like that, it gives you a sense of where certain mineral deposits are.

So, what we’re thinking about with this mining business — and this is, to give appropriate credit, Arron Kallenberg (founder, Wild Alaskan Company)’s idea, something that he thought about after he had come across my work in terms of looking at salmon using magnetic cues to navigate. He was the one who put together the question: As you mine that resource, as you extract it, might that alter the magnetic environment in the vicinity of that resource? A place like Pebble Mine that is near rearing sites of salmon... as the material is removed, does that change the magnetic topography of the landscape in a way that could confuse the salmon? It’s not really been asked ever, so it’s a question worth pondering. 

Whenever you have something in nature that is more difficult and less efficient, that usually means bad things. That usually means mortality is more likely, or finding your foraging grounds is more difficult, or more energy is expended on it so you’re not able to grow as big and fat and healthy… which might mean, for the salmon, you are less likely to have offspring. Or for the fisherman, it means you might be a less valuable catch. 

How consequential would magnetic disruptions caused by mining be to salmon populations, in relation to other disruptions caused by mining?

What we’re imagining tying [our research] to is not so much, “Is this a bigger consequence than copper poisoning?” There’s already plenty to know about mines to know that they’re not great for salmon. You have wastewater running through and silt flowing down, and you completely keep salmon eggs from getting oxygen and they all die off because of runoff from the mine. That’s pretty big, right? And that will get rid of all of them. 

The goal for this is to consider things from a slightly different avenue… to ask the question of, “Even if things go absolutely perfectly, will [removing minerals] fundamentally change an aspect of the salmon’s environment that is important to them?” A good part of this project is presenting that in a way that is that spurs additional research, that spurs additional questions. You’re just adding that bit of information into the things that folks at the EPA or the resource managers [could consider when] assessing potential impacts. Those are the things that should be added to the list.

Arron has posed the question of whether it’s a coincidence for Bristol Bay to be the location of one of the largest mineral deposits as well as one of the largest sockeye salmon spawning sites in the world. What are your thoughts on this? 

Throughout the Pacific Northwest and into Northern Europe, mining sites for obvious reasons might be situated near rivers that salmon use and that fishermen depend on, and so it does seem like there could be this intrinsic conflict between mines and salmon in terms of co-localization, in that both being a good place for a mine, a good place for salmon. Certainly this is likely to be non-random from an economic perspective in terms of mining near a river where you can ship material to and from sites.

An interesting thing to look into would be if [mining sites] are associated with magnetic anomalies — these crustal deposits of iron — it’s conceivable that those could be also places that are consistently navigable from a salmon’s perspective, that maybe those spots could serve as navigational beacons during their freshwater movements. 

At this point in your research, what do you think the likelihood is that mining is significantly disruptive to an animal’s ability to use magnetic cues to complete its migrations?

As the data are coming in, so to speak, it’s probably too early to say anything definitive. My sense is that for the most part the effects will tend to be very localized, and so widespread disruption might not be the thing that you would necessarily predict because of mining, either widespread disruption of the magnetic field or impacts to animals that use it. 

That said, for particular places, for particular species, those impacts might exist and might be of some concern. Namely, if you have the wrong amount of material removed from the wrong location, then those effects could add up to something significant, especially if we’re looking at a system that’s delicately balanced — if the salmon system is a delicate balance in terms of being able to use an already somewhat shifting magnetic map that is tricky to get right under the best conditions, and things [like mining] might tip them one wrong way or another. 

Humans are very disruptive to the natural magnetic environment, and it’s likely that salmon need a fairly clean, pristine magnetic environment the same way that they need clean pristine waters. It’s a different aspect of their life; you need your clean pristine waters to be able to get enough oxygen to breathe, you need a clean pristine magnetic environment so that you can complete your long distance migration

So, as we’re thinking about being better stewards of our world, better stewards of our resources, I think it will take thinking about things from a slightly different perspective than just how can we efficiently and “safely” extract resources, and think more about what in the environment are animals using, what in the environment do salmon need to thrive.