Initial Publication Date: August 12, 2008

Plenty of Fish in the Sea?

Part B: Interpreting Species Density Graphs

The contrast in the level of biodiversity 50 years ago with that of today is striking. By looking at this data over a long time period, scientists were able to differentiate changes in fish population density due to climate change from those due to fishing practices. While environmental changes have been known to visibly diminish the size of fish communities from year-to-year, declines over longer timescales appear to be primarily driven by overfishing.

  1. Examine the graphs below comparing species density and total long-line catch of tuna and billfish by ocean.
  • Look carefully at what is being plotted on each axis of the graphs.
  • Note that the y-axis scales are not the same for total catch in each ocean.



Checking In

Answer the following questions to check your understanding of the information provided in the species density graphs above.
  • Which ocean experienced the largest decline in species density between 1960 and 2000?
  • Which ocean experienced the largest percentage increase in total catch of tuna and billfish between 1960 and 2000?

  • To get a better understanding of why decreased species diversity in the oceans is such a critical issue, read the article Why is Marine Biodiversity Important?.
    • Click on "Vocabulary Help" below for definitions of a few new terms you will encounter in the article. As you read, keep track of any other unfamiliar words you come across. Look up their meanings in the Fisheries Glossary, in a dictionary, or by doing an Internet search.


    Stop and Think

    1: Why is it important to have species diversity in the oceans?

    2: Why do you think large predatory fish are important for maintaining the balance of marine ecosystems? Why are they important to the sustainability of the fishing industry?



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