OceanWorld

Topic: Fisheries 
Theme: Interactions

Key Concepts:

Location of Major Harvesting

  • Fishing is best in coastal areas over the continental shelves and in areas of upwelling.
  • Of the thousands of species of marine fishes, mollusk, and crustaceans only about 500 species are regularly caught and processed.
  • The fishing business employs more than 15 million people.
  • About half of the world's commercial marine catch (1995) is taken by only 5 countries:
    • China = 22%
    • Peru = 13%
    • Chili = 7%
    • Japan = 6%
    • United States = 5%
  • Commercial fishing of the Peruvian anchoveta exceeded 12 million tons in 1971 making it, at that time, the world's largest fishery.

Upwelling, gyres, eddies, temperature, and salinity

  • Where currents encounter seafloor topographic features such as ridges, plateaus, seamounts, banks, or islands, water must flow over or around the feature and nutrient-rich deep water can be mixed into the photic zone by complex eddies and turbulence. The increased productivity caused by interaction of ocean currents with islands can be seen in the increased chlorophyll concentrations around some such islands.
  • Coastal upwelling and land runoff are the two most important mechanisms of nutrient supply to coastal photic zones.
  • Productivity is lowest in the interior of subtropical gyres in each ocean, as these areas are remote from nutrient inputs in runoff.
  • The total fish production of upwelling areas is about 1/2 of the world's total despite the very small area (0.1 percent of the total area of the ocean) in which upwelling occurs.
  • The most successful fisheries are herring, anchovy, and sardine fisheries in upwelling regions, They constitute about 25% by weight of the global catch. Because these species feed primarily on zooplankton at the second trophic level, they are extremely abundant. Their harvest represents an efficient use of ocean resources.
  • Complex interactions of ocean physics, chemistry, and biology cause variations in fish stock.
  • The average trophic efficiency is higher in coastal food webs than in open ocean food webs and is highest in food webs of upwelling areas.