Fishing & Overharvesting
- Explain the tragedy of the commons using fisheries as an example
- Describe overfishing, bycatch, and the promise and problems of aquaculture
- Apply the concept of maximum sustainable yield to a fishery
The tragedy of the commons
The tragedy of the commons explains why shared resources get overused. When a resource — like an ocean fishery — is open to everyone and owned by no one, each user gains the full benefit of taking more (one more boatload of fish) while the cost of depletion is spread across everyone. So each individual is rewarded for taking as much as possible, and the collective result is that the resource is exhausted. Fisheries in international waters are a textbook case: no single nation has an incentive to hold back.
Overfishing and bycatch
Overfishing means harvesting fish faster than they can reproduce, driving populations toward collapse — as happened to the Atlantic cod off Newfoundland, which crashed in the 1990s and has never fully recovered. Industrial methods worsen the damage: trawling drags heavy nets across the seafloor, destroying habitat, and bycatch — the unintended catch of non-target species like dolphins, turtles, and juvenile fish — kills enormous numbers of animals that are simply discarded. Removing top predators can also trigger cascading changes throughout the marine food web.
Aquaculture: solution and problem
Aquaculture — farming fish and shellfish — is the fastest-growing form of food production and can relieve pressure on wild stocks. But it has its own impacts: crowded pens spread disease and require antibiotics, concentrated fish waste and feed pollute surrounding water and can cause eutrophication, farmed fish that escape can disrupt wild populations, and many farmed species are carnivorous, so they must be fed wild-caught fish — sometimes consuming more fish than they produce. Managing fisheries sustainably means fishing at or below the maximum sustainable yield.
A fish population of 100,000 adds about 20,000 new fish through reproduction each year. A fleet begins harvesting 30,000 fish per year. Explain what will happen to the population over time.
- 1.Identify the replacement (recruitment): the population gains 20,000 fish per year.
- 2.Compare the harvest to the replacement: the fleet takes 30,000 per year, which is 10,000 more than are replaced.
- 3.Each year the population therefore falls by about 10,000 (harvest minus replacement).
- 4.Sustained harvesting above the replacement rate drives the stock downward toward collapse — this is overfishing.
Several nations fish the same unregulated stretch of open ocean. Each keeps increasing its catch even though everyone knows the stock is declining. This situation best illustrates:
The tragedy of the commons hinges on two features: the resource is shared/open-access and depletable. Solutions all work by removing one of those — assigning ownership or rights (fishing quotas), or regulating access (catch limits, protected areas). Look for those in answer choices.
Which of the following is an environmental drawback of aquaculture (fish farming)?
For maximum sustainable yield questions, compare the harvest rate to the reproduction (replacement) rate. Harvest ≤ replacement is sustainable; harvest > replacement causes decline. Numbers make it concrete — always state whether the catch is above or below the yearly recruitment.
Answer the 2 checkpoints as you read.
Sign in to save your progress