What are the forces that influence ocean currents? Describe their role in fishing industry of the world. (UPSC 2022)

Ocean currents are large-scale movements of seawater driven by a mix of external forces and internal ocean conditions. They redistribute heat, nutrients and marine life across the seas, and therefore shape major fishing zones of the world.

• Forces influencing ocean currents:
  • Solar heating creates temperature differences and slight sea-level slopes, setting water in motion.
  • Prevailing winds are the main force for surface currents, especially in the top 100 metres.
  • Coriolis force deflects currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
  • Gravity moves water down slopes formed by piling up of water or differences in density.
  • Density differences caused by temperature and salinity drive deep currents and the global ocean conveyor.
  • Continental barriers and seabed relief guide and redirect currents along coasts and basins.

• Role in fishing industry:
  • Mixing of warm and cold currents creates nutrient-rich waters and abundant plankton, which attract fish.
  • Upwelling zones bring cold, nutrient-laden deep water to the surface and support very high fish catches.
  • Best fishing grounds occur where currents meet, such as the Grand Banks, off Japan, Peru, California, Canary and Benguela coasts.
  • These eastern boundary upwelling systems occupy a tiny share of the ocean but contribute a large share of global marine catch.
  • Climate events like El Niño weaken upwelling, reduce plankton, and cause sharp falls in fish harvests.

Thus, ocean currents are both a physical and economic force. They control marine productivity, determine the location of rich fishing grounds, and make fisheries highly vulnerable to climate change and overfishing.