OceanWorld

Topic: Fisheries
Theme: Change

Key Concepts:

Adverse Effects of Human Activity

  • Pollution is the addition of substances to or the alteration of the ocean ecosystem in a manner that is deleterious (harmful) to the ocean ecosystem or its resources.
  • Pollution includes discharge of harmful waste, activities such as overfishing, construction of structures, and other harmful human activities that adversely affect ocean ecosystems by changing currents, distribution of dissolved substances or heat, or sediment transport patterns.
  • Contaminants with large quantities of suspended particles (turbidity) can block the light needed for photosynthesis.
  • Eutrophication occurs when excessive nutrients are present as a result of sewage discharge.
  • Alterations of marine habitats by dams, bulkheads, levees, etc., can alter current patterns, affect sedimentation and prevent some sea life from migrating. Marine diversity is usually limited as a result.

Climate Oscilllations

  • Most of the open ocean has low productivity, the exception being certain high latitude regions and the equatorial upwelling band across the eastern Pacific.
  • High productivity in subtropical and tropical oceans is limited to areas of upwelling.
  • Year to year and several-year oscillations of climate that are related to ocean-atmosphere interactions also have an impact on fisheries. These oscillations involve temperature changes in ocean water that in turn has an effect on upwelling. Two such examples have been studied in the Pacific Ocean.
    • One is related to the vast North Pacific Ocean where surface waters become slightly warmer or cooler than normal for a period of years.
    • The other is called El Nino, which originates in the tropical Pacific Ocean and is associated with climate changes over much of the globe.
  • With the onset of El Nino, water temperatures offshore Peru rise noticeably, nutrient levels drop, phytoplankton populations plummet, and anchoveta (anchovies) become scarce. Some of the larger fish migrate to cooler water. Many birds and mammals suffer from lack of food resources and die of starvation.