Remix clone Hacker News

Salmon have no "genetic memory" - if you release baby salmon from a hatchery that were bred from adults caught elsewhere, they remember where they were released- not where they are genetically from-, and swim back to the area of the hatchery. It appears to be regular memory learned from experience. It is believed to be mostly chemical sensing, e.g. specific smells that they are remembering and returning to.

Salmon are not 100% effective at making it back to their birthplace, and some small fraction stray randomly- which is what allows them to populate new areas and re-populate others where they were wiped out. This article isn't about a lot of salmon - only hundreds, so this is probably the amount that would naturally stray to this region from others, with or without a healthy returning population.

For example, some ~120k chinook salmon returned to the Columbia river this year, so if 0.01% of them strayed to the Klamath river, you'd get about this many.

▲

soulofmischief 4 days ago | parent [-]

Salmon have also displayed possible geomagnetic navigation capabilities, similarly to homing pigeons.

https://royalsocietypublishing.org/doi/10.1098/rsbl.2017.075...

▲

tyre 4 days ago | parent [-]

This is how sea turtles do it, too, and why sea turtle release has to happen on the beach despite the higher risk of predators.

They get sand up their nose and calibrate based on the magnetism of the iron, iirc

▲

PittleyDunkin 4 days ago | parent [-]

Humans may be capable of geomagnetic sensing as well. As a human myself, I've got to imagine this is extremely difficult to control for sensing vs other forms of navigation (sun, stars, moon, wind, animal migration, etc.)

▲

soulofmischief 4 days ago | parent [-]

Well for example we've shown that red foxes have strong preference to pouncing in a north-eastern direction, and in other directions their accuracy plummets. It's believed that this is due to geomagnetic sensing.

We've studied how the blue photoreceptors in our retinas are actually magnetoreceptive, meaning in the right conditions, suspended in a fluid, they'll align the the Earth's magnetic field just like a compass needle.

I'd read before that this technique was theorized to be used in fruit flies, with the photoreceptors suspended in a fluid in the eye. But more recent studies have failed to replicate the geomagnetic sensing capabilities of fruit flies.

It's still nuts to imagine what that might look like. Distortions in your vision from magnetic sensing sounds so neat.

▲

wbl 3 days ago | parent [-]

So when will prey evolve to always face southwest?

▲

soulofmischief 3 days ago | parent | next [-]

Oh well that's the funny thing, Southwest is the next best direction given that it's on the same axis as northeast.

> a large majority (74%) of successful attacks in high cover were confined to a cluster centred about 20° clockwise of magnetic north with a small (15%) secondary cluster at due south, while attacks in other directions were largely unsuccessful.

https://pmc.ncbi.nlm.nih.gov/articles/PMC3097881/ (there's a nice little chart showing angular preference.

The researchers also mention a previous study they'd worked on in the first paragraph of the introduction, dealing with the geomagnetic alignment of grazing cattle. I hadn't read this one before so I took the time, and it's equally fascinating. https://pmc.ncbi.nlm.nih.gov/articles/PMC2533210/

▲

wbl 3 days ago | parent [-]

If the fox jumps northeast preferentially prey facing that way will see the fox more often. There is some equilibrium here I can't calculate but that was the thinking behind my joke.

	▲	soulofmischief 3 days ago \| parent [-]
		Oh, yeah that went over my head, that's actually pretty funny.

▲

noworriesnate 3 days ago | parent | prev [-]

This is actually a common tenant of rabbit religions FYI