Pacific salmon are fascinating to study, because their lifecycle is so interesting. They hatch in freshwater streams, at which point they are called alevin. Although they have hatched, they still have a yolk sac upon which they feed. Once they have absorbed the yolk sac, they are called fry, and they begin feeding on the plankton in the stream. They eventually mature into parr, which are also called fingerlings. After about 12-18 months in freshwater, they move to the brackish waters of estuaries, ecosystems where freshwater rivers meet the ocean. At this point, they are usually called smolts. After a few months, they venture out into the ocean, where they will spend several years growing.
The amazing part, of course, is that after spending several years in the ocean, they return to the same freshwater stream where they hatched to spawn another generation. From a scientific point of view, one of the most important questions you can ask about this lifecyle is, “After spending years in the ocean, how do the salmon know the way back to the freshwater stream in which they hatched?” It makes sense that while they are fry and parr, they get a good sense of the mix of chemicals that make up their “home stream,” but they obviously can’t follow that trail of chemicals from the ocean! So how do they get from the ocean to the correct estuary so that they can get back to the stream in which they hatched?
About a year ago, I discussed a study that gave a partial answer to that question. It showed that sockeye salmon use the earth’s magnetic field as a “map” that leads them to the proper estuary. The study suggested the salmon had other means of navigation at their disposal, but the magnetic field was a very important tool in the fish’s repertoire. How do the salmon acquire this map? In the previous study, it was suggested that the map is imprinted in the salmon’s brain as it is traveling from the estuary to the open ocean.
Well, the same research team has done a follow-up study, and they have decided that this suggestion is probably not correct. Instead, the real story is more complex and much more interesting!
In this new study, Nathan Putman and his colleagues constructed a large platform that had copper wires laid out in a grid around its edge. By running currents through the wires, they were able to produce magnetic fields that were characteristic of the magnetic fields that Chinook salmon encounter while swimming in the ocean. They then put young salmon (parr) in five-gallon buckets on the platform. They allowed the fish to acclimate to their buckets, and then they used the wires to produce a magnetic field that would be characteristic of what the salmon would encounter once they got to the ocean and reached the northern limit of their typical range. In the presence of that magnetic field, the parr preferentially oriented themselves in a southerly direction.
When they changed the magnetic field so it was characteristic of what the salmon would experience in the southern limit of their typical oceanic range, the parr preferentially oriented themselves in a northerly direction. In the presence of no magnetic field, they had no preference for their orientation. Of course, this provides even more evidence that the salmon use the earth’s magnetic field in order to navigate back to their home stream.
But remember, in the parr stage, the salmon have never been to the estuary. They have only been in their home stream. They must mature to the smolt stage before going to the estuary. So despite the fact that the fish had never seen the estuary or the ocean, they already knew how to use the magnetic fields in the ocean to guide them to the estuary! How is that possible? According to the authors:1
Even so, without the opportunity to learn gradients in magnetic intensity and inclination angle, the response to the change in magnetic field parameters must be inherited. It is particularly noteworthy that the fish tested were parr, the stream-dwelling juvenile stage. Thus, it appears that the fish possess orientation responses necessary for successful ocean navigation prior to even migrating toward the sea. (emphasis mine)
In other words, the fish actually inherit their magnetic maps from their parents!
Now the authors are quick to point out that this inherited map is probably just a “first draft” of the map they will actually use to make it home. As the fish mature in the estuary and venture out into the ocean, other environmental details are probably added to increase the accuracy of their navigational abilities. Nevertheless, the study provides strong evidence that the basics of salmon migration are not learned. They are inherited!
The more I learn about creation, the more I stand in awe of its Creator.
REFERENCE
1. Nathan F. Putman, Michelle M. Scanlan, Eric J. Billman, Joseph P. O’Neil, Ryan B. Couture, Thomas P. Quinn, Kenneth J. Lohmann, and David L.G. Noakes, “An Inherited Magnetic Map Guides Ocean Navigation in Juvenile Pacific Salmon,” Current Biology 24(4):446-450, 2014
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Hmmm. This makes me wonder.
I assume that the salmon in this study were taken from North America.
Are there South American Salmon that are born in streams feeding the Pacific Ocean, that then migrate to southern waters as adults, and then go back to their home streams to spawn?
If you did this same experiment on parr of these South American salmon species, using the magnetic fields of their typical range (different from the North American salmon) would they again orient themselves correctly?
Seems like that would be a good way to confirm this experiment, but might require more budget than they have for these experiments.
David, Chinook salmon (the same species as in the study) were brought to South America for aquiculture (raising fish for food). So there are several populations that have the same lifecyle in South American streams that feed the Pacific. Your suggestion is an excellent one and could be done. The lead author on the study is the contact person. You can click on the envelope next to his name here to send him your suggestion. If you would rather not do that, I will.
Dr. Wile, thank you for the encouragement. I just thought it would be interesting to do this experiment on salmon that had come from a different magnetic environment. I’m willing to contact them with my suggestion, if it’s Ok to tell them you sent me and link back to this blog. 🙂
Continuing my thought…
My understanding is that Chinook salmon from Oregon, Washington, and the Canadian west coast basically leave the river mouths and turn north heading for colder waters. I googled “chinook salmon migration patterns” and got this map image illustrating:
http://www.pac.dfo-mpo.gc.ca/fm-gp/species-especes/salmon-saumon/facts-infos/chinook-quinnat-eng.html
I assume that chinook salmon from South America would leave the river mouths and turn *south*, heading for colder waters in that direction. That’s a really big difference in the magnetic map they would follow, and so should be show a striking difference from their northern neighbors.
Sorry if I’m bothering you with too many posts… this subject just resonated with me, since I grew up in Oregon.
If the chinook salmon were brought to South America relatively recently, then it would be fascinating to learn how many generations it takes for the salmon to acquire a new inherited magnetic map different than the one they originally acquired from their northern ancestors.
Hmm.
Feel free to link back to this blog, David. I would have contacted him to make the suggestion, but since it was your idea, it makes sense that you should.
Remember that the authors say there are probably other evironmental cues that add to the salmon’s navigation. I suspect that when the South American salmon first hit the ocean and saw a completely foreign map, they probably used environmental cues to navigate. This was probably less efficient, causing many to not return. However, after a few generations, you would expect a new map to be produced for inheritance.
You most certainly aren’t bothering me with your comments. I enjoy discussing such things.
That’s so awesome! 😀
“If the chinook salmon were brought to South America relatively recently, then it would be fascinating to learn how many generations it takes for the salmon to acquire a new inherited magnetic map different than the one they originally acquired from their northern ancestors.”
probably wouldn’t take long…one thing’s for sure; the fish wouldn’t have to wait around for a random mutation to accidentally pop up.
That article has a comments section. Someone else commented there and Nathan Putnam himself replied. So I went ahead and posted my own suggestion there as well. It is awaiting moderation.
Excellent, David! I will be interested to see what he says.