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.- 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.
- Which ocean experienced the largest decline in species density between 1960 and 2000?
To determine how much species density declined in each ocean between 1960 and 2000, use the following formula:
decline in species density (%) = species density (%) in 1960 - species density (%) in 2000
Example: The decline in species density in the Indian Ocean between 1960 and 2000 was 30% (80% - 50%). - Which ocean experienced the largest percentage increase in total catch of tuna and billfish between 1960 and 2000?
To determine the percentage increase in total catch for each ocean between 1960 and 2000, use the following formula:
% increase = 100% x (catch in 2000 - catch in 1960)/catch in 1960
Example: The percentage increase in total catch in the Pacific Ocean between 1960 and 2000 was 233% (100% x (500 - 150)/150). - 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.
- polysaccharide
- A complex carbohydrate such as cellulose, starch, or glycogen.
- sessile
- Attached directly by the base, and not raised upon a stalk (e.g., a sessile leaf); Permanently attached or established, not free to move about (e.g., sessile sponges and coral polyps).
- phyletic
- Of or relating to evolutionary change in a single line of descent without branching.
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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