Impacts of Overfishing (College Board AP® Environmental Science): Study Guide

Impacts of overfishing on aquatic biodiversity & human populations

What is overfishing?

• Overfishing occurs when fish are harvested at a rate faster than they can reproduce

  • This leads to population declines

• It threatens marine and freshwater ecosystems, affecting both biodiversity and human livelihoods

Impacts on aquatic biodiversity

Decline in fish populations

• Overexploitation of key species reduces fish stocks, disrupting marine food chains

  • Example: Atlantic cod populations collapsed in the 1990s due to excessive fishing, forcing long-term fishery closures

Disruption of ecosystems

• Removing too many fish alters predator-prey relationships, causing trophic cascades

  • Trophic cascades occur when disruptions at one level of the food chain trigger indirect effects on other species and habitats

  • Example: The loss of large predatory fish (e.g., sharks) allows prey species, such as rays, to overpopulate

    This can lead to overgrazing of important marine vegetation, like seagrass beds, which serve as nurseries for many marine species

Habitat destruction

• Destructive fishing practices such as bottom trawling destroy seabed ecosystems

• Coral reefs and seafloor habitats suffer long-term damage, reducing shelter for marine life

Impacts on human populations

Food security concerns

• Overfishing reduces the availability of seafood

  • This can threaten coastal communities reliant on fish as a protein source

  • Example: Some West African nations have seen declining fish stocks due to industrial-scale overfishing, impacting local diets

Economic consequences

• Fisheries collapse leads to job losses and declining incomes for millions in the fishing industry

  • Example: The Northwest Atlantic fisheries collapse devastated economies dependent on cod fishing

Social and geopolitical conflicts

• Competition for dwindling fish stocks has led to disputes over fishing rights and illegal fishing practices

  • Example: The South China Sea dispute involves multiple countries overfishing in contested waters