Plenty of Fish in the Sea?
Part A: Exploring Biodiversity Maps
People have been catching fish from the ocean for thousands of years. It was only recently (in the 1950's) that anyone started keeping records of the numbers and types of fish they caught. In 2005, scientists gathered as much of this data as they could and used it to produce global maps of fish distributions over time. One of these maps showed the distribution of two large predator fish species, tuna and billfish. Further analysis of the datasets showed that the concentration of tuna and billfish was a good indicator of overall marine biodiversity, or variety of life in the oceans. The map data were reinterpreted to show species density. We can now use these maps to see how marine biodiversity has changed over time.
- Click on the thumbnail image below of the global marine biodiversity map for the 1960s. Familiarize yourself with the color codes and identify one place on the map where species density is especially high and one where species density is particularly low.
The species density index reflects the expected number of species per 1000 fishing hooks for a given area of ocean.
- Download the 1960s map, keeping the default image name when saving the image to your computer.
- Click on the thumbnail to open the image of the 1970s map. Are there any obvious differences between this map and the 1960s map?
- Download the global marine biodiversity maps for the 1970s, 1980s, and 1990s, again keeping the default image names.
- Open the four biodiversity map images as a chronological sequence using ImageJ.
- From ImageJ's menu bar, choose File > Import > Image Sequence... and navigate to the folder where you stored the downloaded biodiversity maps. Select the "1960sbiodiversity" image and click Open.
- A Sequence Options dialog box will appear. In the box next to Number of Images: enter the number "4". In the box next to File Name Contains: type in the word "biodiversity". Leave all other boxes with their default values and click Okay.
- Look at the color scale below the map to figure out where the greatest concentrations of fish are.
NOTE: This step puts all four images into a single window named Stack. You can flip between the images by dragging the slider button along the bottom of the stack window, or by pressing the greater than ">" or less than "<" keys on your keyboard.
- Use the < and > keys to flip through the stack of images to examine them one at a time.
- From ImageJ's menu bar, choose Image > Stacks > Animation Options....
- In the box next to Speed (0.1-100 fps): enter the number "2". Check the box next to Start Animation. Make sure the box next to Loop Back and Forth is not checked. Click Okay.
Stop and Think
1: How does the overall color of the map change over time? What does this imply about the overall diversity of fish in the sea?
2: Can you identify any "hotspots" or areas with larger concentrations of species diversity than the surrounding ocean? Do they persist over time?