Tragedy of the Commons and Overfishing

The tragedy of the commons

A commons is a resource that nobody owns but everybody can use: the open ocean, the air, a public pasture, a river. Two features make a commons risky. Anyone can use it, and one person's use leaves less for everyone else.

The logic is simple. Each fisher thinks: "If I don't catch these fish, someone else will." Each one's gain is private. Each one's cost is shared. So everyone takes more, and the resource collapses.

Real examples include overfished oceans, overgrazed public rangeland, and groundwater pumped from a shared aquifer. Air and water pollution are the same problem in reverse: each polluter gets a cheap place to dump waste, and everyone pays.

Overfishing and bottom trawling

Overfishing means catching fish faster than the population can reproduce. The open ocean is a classic commons. The Atlantic cod fishery off Newfoundland collapsed in the early 1990s, and fishing communities in New England have also faced severe cuts to cod catches.

A fish population can replace itself only up to a point. The maximum sustainable yield (MSY) is the largest harvest that a population can replace each year. To keep the math simple, the example below assumes the population can replace 10% of itself per year, and that rate sets the sustainable harvest. A harvest at or below the sustainable level can be replaced, and a harvest above it cannot.

Bottom trawling drags a large weighted net along the ocean floor. It catches shrimp and groundfish, but it:

• scrapes and destroys habitats such as corals and sponges,

• stirs up sediment,

• causes bycatch: unwanted fish, sea turtles, and marine mammals caught and thrown back, often dead.

Managing fisheries and forests

If the problem is that nobody controls access, the solution is to add rules.

Fishers often resist these rules because they cut income in the short term. Over the long term, though, a healthy fishery keeps jobs. Catch per boat is a useful measure: if the total catch stays high but each boat catches less, boats are working harder for fewer fish, which signals a shrinking population.

Forestry

Clearcutting removes all the trees in an area. It is cheap and fast, but it exposes the soil. Rain washes it away (erosion), and sediment and nutrients flow into nearby streams, making them cloudy and warmer, which harms fish. Habitat is lost, and the forest takes decades to regrow.

Selective cutting removes only some mature or chosen trees. Roots hold the soil, shade remains, and wildlife habitat survives. The disadvantage: it is slower and more expensive, and building roads for access still causes damage. Sustainable forestry harvests no faster than trees regrow and often replants.

Mining and its impacts

Mining removes minerals and fuels from the ground. The material containing the valuable mineral is ore. The rock and soil removed to reach it is overburden. The waste left after the mineral is separated is tailings.

Surface mining is used when the resource is near the surface.

• Open-pit mining: a huge pit, as in copper mines in Arizona.

• Strip mining: the overburden is removed in long strips to reach a flat layer, such as coal.

• Mountaintop removal: explosives blast off the top of a mountain to reach coal seams, and the debris is dumped in nearby valleys. It is common in Appalachia.

Subsurface mining reaches deep resources through shafts and tunnels. It disturbs less land but is more dangerous for miners and more expensive.

Environmental impacts

• Land: habitat destruction, erosion, large piles of waste rock and tailings.

• Water: rain on exposed rock carries sediment and metals into streams. Acid mine drainage forms when water and oxygen react with sulfur-containing minerals such as pyrite, producing sulfuric acid. The acidic water dissolves heavy metals and can kill aquatic life for decades.

• Air: dust and emissions from machinery and blasting.

Reclamation means restoring mined land by regrading the surface, replacing topsoil, planting vegetation, and treating water. It reduces erosion and runoff, but it rarely restores the original ecosystem: soil structure, species mix, and groundwater flow are hard to rebuild.

Summary

Back to the start: on the open lake, the fix is rules everyone follows, such as quotas and protected areas, so that one person's extra fish no longer comes at everyone else's expense.