OceanWorld

Topic: Fisheries
Theme: Measurement

Key Concepts:

Primary Productivity

  • Plant photosynthesis converts inorganic carbon of carbon dioxide into the organic carbon of sugar, Primary productivity is the total quantity of carbon fixed by plants, expressed as grams of carbon fixed per square meter of sea surface per unit time (gC/m2/yr).
  • If plants are plentiful in the water of an area, animals will be plentiful. The absence of plants means a scarcity of animals.
  • Fish depend on primary production for their food; therefore fish are more abundant in areas where primary productivity is high.

Size of Harvest

  • Many of the major fisheries are being exploited at or near their maximum sustainable yield and many are overfished.
    • The U.S. National Marine Fisheries Service estimates that 45% of the fish stocks whose status is known now suffer from overfishing--so many fish have been harvested to the point that there is not enough breeding stock left to replenish the species.
    • Commercial extinction is the depletion of a resource species to a point where it is no longer profitable to harvest.
  • A substantial increase in world fisheries catch would be detrimental to the ocean ecosystem--especially on higher carnivores (large meat-eating fish, marine mammals, and sea birds),
  • About 40% of the global fisheries catch of all species are used as animal food.
  • It may be impossible to predict future fish stocks accurately (just as it is impossible to forecast weather accurately more than a day or two in advance).

Satellite Measurements of Chlorophyll and Phytoplankton

  • When biologist at sea take water samples or do plankton tows, the measurements are from but a small spot within the vast ocean. Other samples taken from other locations are compared and compiled to create an overall representation of the amount of phytoplankton available.
  • Coastal Zone Color Scanners (CZCS) mounted on satellites detect different bands of visible color emitted from the ocean's surface water. Variations in color reflect mainly differences in the concentrations of chlorophyll, the principal photosynthetic pigment in plants. Because chlorophyll reflects a green light, large concentrations are indicated on the images by green colors and sparse concentration in blue colors. This is an indirect measure of the abundance of phytoplankton.
  • Because satellites can cover Earth's oceans within a period of days, scientists are able to get a more complete picture or measurement of primary productivity.