"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.
Tuna from the ocean at large may be a "commons", sure, but helium comes from natural gas deposits, which tend to be in areas where one nation or another claims exclusive rights to said deposits, treats them like property, and seeks to maximize the value they can extract from them (while still competing with other resource-holders in a market).
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.
Fishing, at a low enough volume, it is sustainable, which humans have been doing for dozens of millennia.
The problem comes when the threshold is reached and passed. That is specifically the tragedy of the commons. It's a fractal problem - i.e., even if one country fixes the issue through regulation/taxes/prohibition, another country may still overfish a shared body of water.
The "full cost" wouldn't need to be replacing each fish caught. It would be a fee/tax to ensure a sustainable fish population - this could still result a reasonable market for fish.
>The "full cost" wouldn't need to be replacing each fish caught. It would be a fee/tax to ensure a sustainable fish population - this could still result a reasonable market for fish. //
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.
