Prevolio
Game theoryClassroom · multi-user

Tragedy of the Commons — The Fishery

A shared fishery everyone harvests from: each round, decide how much to catch and watch whether the stock survives the class or collapses.

You’ll learn: Feel the conflict between individual gain and collective sustainability, and why rules or quotas exist to manage shared resources.

Teacher guide

Students will learn to

  • See how a shared resource everyone draws on gets depleted when each person acts in their own interest.
  • Feel the tension between catching more now and leaving enough for the stock to regrow.
  • Understand why rules, quotas, or communication (Ostrom) are needed to avert collapse.

Before the session — ask

  • If a lake's fish regrow slowly, what happens if everyone fishes as much as they want?
  • Whose interest is it in to hold back — and why might no one actually do it?

After the session — discuss

  • Did the stock survive the rounds, or collapse? What drove the outcome?
  • How much could the class have sustainably harvested each round versus what it actually took?
  • What rule — a quota, a tax, a shared agreement — might have kept the fishery alive?

Timing

  • Briefing & the rules3–5 min
  • Six harvest rounds8–12 min
  • Debrief & discussion8–10 min

Run it with your class

Students join with a code or QR — no account needed. Teachers start a session from the dashboard.

Join with a codeFor teachers

What is the tragedy of the commons?

The tragedy of the commons describes how a shared resource that no one owns tends to be overused and destroyed, even though everyone would be better off preserving it. Picture a fishery that a whole community harvests from. Each fisher who takes one more fish gets the full benefit of that catch, but the cost — a smaller, less renewable stock — is spread across everyone. Because the private gain is concentrated and the cost is shared, each individual is drawn to harvest more, and when everyone follows that logic the stock is depleted below the level that would regenerate — overharvesting past the sustainable yield. The resource collapses, and all are left worse off than if they had restrained themselves. This is a negative externality problem tied to a common-pool resource: rivalrous (my catch leaves less for you) but non-excludable (no one can be kept out). It explains overfishing, deforestation, groundwater depletion, and pollution. The classic remedies change the incentives — assigning property rights, setting quotas or taxes, or building community rules and monitoring — so that the cost of overuse is felt by whoever imposes it, letting a shared resource survive.

How the simulation shows it

Each round you and the class decide how much to catch from a shared fishery, and watch whether the stock regenerates or collapses. Choosing your own harvest while everyone else fishes hard makes the conflict vivid: catching more helps you now, but if all do it the stock crashes and everyone loses.

Common misconceptions

Frequently asked questions

What is the tragedy of the commons?
The tendency for a shared, unowned resource to be overused and depleted because each user gains fully from taking more while the cost of depletion is shared by all.
Why does the resource collapse?
Because each individual's incentive is to harvest more — they get the full benefit while the cost falls on everyone — so collective harvesting exceeds the sustainable yield and the stock crashes.
What is a common-pool resource?
A resource that is rivalrous (one person's use leaves less for others) but non-excludable (no one can easily be kept out) — like a fishery, forest, or aquifer, which makes it prone to overuse.
How is this a negative externality?
Each extra unit harvested imposes a cost — a smaller future stock — on everyone else that the harvester doesn't bear. That uncounted cost is why the resource is overexploited.
How can the tragedy be avoided?
By changing incentives: assigning property rights, setting quotas or taxes, or building community rules and monitoring, so the cost of overuse falls on whoever causes it.

Related concepts