salmon returning to same river

For no particular reason, I was wondering the other day about salmon returning to the same river/stream in which they were hatched in order to spawn. In particular, how has it been proved that this is what happens? Are there enough genetic differences between the salmon spawning in two nearby rivers that allow researchers to tell them apart with certainty? Just curious.

This report from ABC News suggests that research done showed that salmon literally smell their way to the right river. Not all salmon pick the right, “home” river, mind, but the scientists apparently tested the ielement traces within the fish to that of the home river.

Some more info here.

When I was a young strapping,sturdy chap('bout 16). I worked at a Salmon hatchery for about a week. They took a certain amount of young salmon , clipped the adipose fin(for ID when they return as adults) and a machine implanted a teeny-tiny,for lack of a better word,plug. On this plug thingy was a bar code. when the adult salmon returned they are ID’d by the missing adipose fin. They’re dissected and the bar-codded plug is examined under a microscope(for what info I never fully understood)…

Here is some information about tagging fish. I think the PIT (passive integrated transponder) tag is the same technology as ID chips used on pets. (And soon, humans.)

[semi-related anecdote]My elementary school used to participate in a program to “re-populate” a nearby river with salmon. While doing a web search for the above link I found that there has never been a salmon poulation there in the first place, or any other river this far south. :rolleyes: [/anecdote]

Thanks for the replies. I figured it wouldn’t be practical to tag the fish externally, but it never occurred to me that they’d use implants. Makes sense, though I suppose the “return” rate is quite low, due to the high percentage of the little fishies being eaten, dying of disease, and what not.

PITs for humans, you say?

PITs for humans? Yes, for example as proposed by BZ00000 in the An End to Crime thread.

As sinister as it sounds, some people think it’ll be a useful thing to have. Check out this article:,1848,55999,00.html

From a link given in that wired article, some people apparently believe it’s quite sinister indeed:

I suppose such fears could be allayed by implanting the PITs in people’s abdominal cavities, just like they do with the salmon. But then people would have to rub their bellies on ATMs in order to withdraw cash. Hmm.