"Markets" only work when there is a seller, and neither helium nor tuna have a seller.

The price of Tuna is set of "how expensive is it to produce a can of tuna" rather than "how many tuna are left in the ocean". In fact, the lower the production cost of tuna fishing, the higher the risk that we empty the ocean of all the tuna.

It's really a problem of the Tragedy of the commons. There is no cost of tuna in the ocean, except the cost of fishing it. So it's a commons, and it will be overexploited.

http://en.wikipedia.org/wiki/Tragedy_of_the_commons

also: be sure to understand http://en.wikipedia.org/wiki/Collapse_of_the_Atlantic_northw...

If those harvesting tuna had to meet the full cost, ie they had to replace the tuna, then tuna would be more expensive. The price doesn't reflect the cost because the planet/ecosystem is being robbed.

If I sell fruit but I get it by stealing it from a neighbour then I'll be able to afford to sell the fruit at a far lower cost than the cost of manufacture and still get a profit.

Partly because 59% of the tuna Americans eat isn't actually tuna: http://www.theatlantic.com/business/archive/2013/02/59-of-th...

There are lots of different types of tuna, some much more expensive than others. The tuna people talk about that is running out and that is used for things like high end sushi is Bluefin tuna which is very expensive. The stuff you get in cheap cans is either Skipjack tuna or Bonito (which are not technically tuna fish) both of which are cheap and relatively plentiful.

AFAIK just big tuna is expensive, like a large whole fish. What you get in the cans are small tuna.