5.2 World Fisheries

2026 📋 Syllabus Objectives

By the end of these notes, you should be able to:

  1. Outline the distribution of major ocean currents
  2. Explain the distribution of major marine fish populations
  3. Describe the El Niño Southern Oscillation (ENSO) phenomenon and its effects on fisheries along the Pacific coast of South America
  4. Identify the position of major cold and warm ocean currents on a map (you do not need to remember their specific names)

📖 Main Content

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1. Distribution of Major Ocean Currents

What is an ocean current?

An ocean current is a continuous, directed movement of seawater flowing through the ocean — think of it like a river flowing inside the sea. These currents move enormous amounts of water across the planet and have a huge impact on climate, weather, and marine life.

What causes ocean currents?

Ocean currents are driven by two main forces:

  • Wind — Strong, consistent winds at the surface of the ocean push the water along, creating surface currents. These affect the top layer of the ocean (roughly the top 100–200 metres).
  • Differences in temperature and salt content — Cold water is denser (heavier) than warm water, and salty water is denser than less salty water. This means cold, salty water sinks and moves along the ocean floor, while warmer, lighter water rises to the surface. This is called thermohaline circulation (thermo = temperature, haline = salt).

Warm and Cold Currents

Ocean currents are classified as either warm or cold:

  • Warm currents flow away from the equator (towards the poles). They carry warm tropical water towards cooler regions. They generally flow along the eastern coasts of continents in the northern hemisphere and the western coasts in the southern hemisphere.
  • Cold currents flow towards the equator (from the poles). They carry cold polar water towards warmer tropical regions. They generally flow along the western coasts of continents in the northern hemisphere and the eastern coasts in the southern hemisphere.

General Pattern of Ocean Currents

Ocean currents follow large circular patterns called gyres. These are giant loops of moving water:

  • In the Northern Hemisphere, gyres move in a clockwise direction.
  • In the Southern Hemisphere, gyres move in an anti-clockwise direction.

This means:

  • Warm currents generally travel from the tropics up the eastern sides of ocean basins (for example, up the east coast of North America, or up the east coast of Asia).
  • Cold currents generally travel from polar regions down the western sides of ocean basins (for example, down the west coast of South America, or down the west coast of southern Africa).

🗺️ Key Exam Tip: You do not need to remember the names of specific currents (like the Gulf Stream or the Humboldt Current). You just need to be able to identify on a map whether a current is warm or cold, and roughly where it is located.

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