Eyes in the Sky II > GIT Web Course > Module 3 > Week 12 > Exploring Ocean Data with GIS > Exploring Ocean Data with AEJEE

Week 12: Comparing Geospatial Tools

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Exploring Ocean Data with AEJEE

An olive ridley sea turtle, named Shadow Dancer, with her satellite telemetry device attached. She was the first sea turtle tagged for the Project Migration 2008 nesting season. Image Source: Whalenet.

Olive ridley sea turtles (Lepidochelys olivacea) are named for their olive colored shell or carapace. They look very similar to the closely-related Kemp's ridley sea turtle. Adult olive ridley turtles can weigh up to 110 pounds and are approximately 24 to 30 inches long. Hatchlings, or baby turtles, weigh only a few ounces. It is believed that olive ridleys have lifespans averaging around 50 years in the wild. While olive ridleys are the most abundant sea turtle species in the world, they are currently classified as endangered.

Like other sea turtles, they do not breed until 10 to 15 years of age. At that time, they return to the beaches of their own youth to lay their eggs. They lay hundreds of eggs in each nest. The peak nesting season for olive ridley turtles in the Eastern Pacific is during the months of September and October. These turtles have adapted a nesting strategy of safety in numbers. Typically, they arrive at their nesting sites in large groups. The turtles gather offshore and come ashore as a group to nest, an event called an arribada, which is Spanish for arrival. Often, hundreds of thousands of turtles will nest at the same location and time. While this provides some safety against predators, it also makes the turtles vulnerable to environmental disasters, such as oil spills and predation by humans. No other turtle has been observed nesting in such a synchronous manner as the olive ridley. After females lay their eggs, they return to the sea and continue to forage. Hatchlings migrate to the ocean around 60 days after the eggs are laid.

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Download the Compressed File of GeoTiff Images and Data about Ridley Turtles

  • Right-click (Win) or control-click (Mac) the link below to download the zipped file of data and images.
    RidleyTurtlesAE.zip (Zip Archive 2.6MB May3 10)
  • Unzip the file. A folder called RidleyTurtlesAE will be created.
  • Move the entire RidleyTurtlesAE folder into the Data folder inside the AEJEE folder. (Path: ESRI/AEJEE/Data/RidleyTurtlesAE)

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Launch AEJEE and Add Data Layers

AEJEE_logo
  • Launch AEJEE by double-clicking its icon on your desktop or by clicking its icon in the dock (Mac) or Launch Bar (Win).
  • To add a September 2008 Sea Surface Temperature image, click the Add Data add layer button button. Navigate to the RidleyTurtlesAE folder. Click once on Sept2008SeaSurf.TIF to select the image. Then click OK.
  • Repeat the procedure to add the Sept2008Chlorophyll.TIF image.
  • Uncheck the 2008 Sea Surface Temperature layer to turn it off and make sure that the Chlorophyll layer added. Then turn the 2008 Sea Surface Temperature layer back on.
  • Last, click the Add Data add layer button button and navigate to the World folder. Click once on country06.shp to select it. Then click OK.
    1. Click the Add Data add layer button button.
      1 add data 1
    2. Navigate to the Data folder.
      2 add data
    3. Navigate to the RidleyTurtlesAE folder.
      3 add data
    4. Click once on Sept2008SeaSurf.TIF to select the image. Then click OK.
      4 add data sst 9 2008
    5. Repeat the procedure to add the Sept2008Chlorophyll.TIF image.
      6 add sept 2008 chlorophyll
    6. Both images are now on the map. The Sept2008SeaSurf.TIF image has been turned off to view the Sept2008Chlorophyll.TIF image.
      7 sept 2008 chloro displayed
    7. Click the Add Data add layer button button and navigate to the World folder.
      navigate to world folder
    8. Click once to select country06.shp. Then click OK.
      choose country 06

  • Move the country06.shp layer to the top of the list and edit its properties to display it with a light gray fill and a dark gray outline.
    1. Right-click (PC) or contro-click (Mac) on the name of the layer (country06.shp) and select Move layer > Move to Top.
      8 move country layer to top
    2. Right-click (PC) or contro-click (Mac) on the name of the layer (country06.shp) and select Properties.
      9 edit properties of country 06
    3. In the Properties window, choose Light Gray for the fill color and Dark Gray for the outline color. Then click OK.
      10 edit properties of countries menu

The map now shows countries of the world layered onto the 2008 sea surface temperature and chlorophyll images.


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Add Event Theme Data for Ridley Sea Turtles

Add Ridley Turtle data from 2008

To map the 2008 Ridley Turtle tracks using Longitude and Latitude coordinates, choose View > Add Event Theme. The Add Event Theme window opens. Click the Browse browse button button to navigate to the file named RidleyTurtles08.csv. (Path: ESRI/AEJEE/Data/RidleyTurtlesAE/RidleyTurtles08.csv). Choose Longitude for the X Field and Latitude for the Y Field. Draw the events using symbols that are White Circles with a point size of 5. The options in the Add Event Theme window are as follows:

  • Table: ESRI/AEJEE/Data/RidleyTurtlesAE/RidleyTurtle.csv
  • X field: Longitude
  • Y field: Latitude
  • Draw event using symbol with:
    • Style: Circle
    • Color: White
    • Size: 5
  • The Output Directory defaults to the current folder that you opened the Turtle file from. Accept this default.
  • Click OK.
  1. Select View > Add Event Theme.
    13 view > add event theme
  2. The datasets are within the RidleyTurtlesAE data folder. Click the Browse browse button button.
    14 click browse button
  3. Navigate to the RidleyTurtlesAE data folder.
    17 nav to data 3
  4. Click once on the file named RidleyTurtles08.csv to select it. Then click Open.
    18 nav to data 4
  5. In the Add Event Theme window, define the coordinates and set the color and the size of the map symbols for the new features.
    • Table: Applications/ESRI/AEJEE/Data/RidleyTurtlesAE/RidleyTurtles08.csv
    • X field: Longitude
    • Y field: Latitude
    • Draw event using symbol with:
      • Style: Circle
      • Color: White
      • Size: 5
    • The Output Directory defaults to the current folder that you obtained the turtle file from. Accept this default.
    • Click OK.
    20 editing fields of csv

  • The 2008 olive ridley turtles will now be displayed on the map as white dots.
    21 turtles on map in white

Note: If you enter the X and Y fields incorrectly, the data will either not project or will project incorrectly. Also, remember that when AEJEE imports and projects a tabular dataset onto a map, it automatically creates and saves a corresponding shapefile. The next time you want to see this dataset on your map as a layer, just click the Add Data button and look for the shapefile of the same name as the original table in the Ridley Turtles folder. For the 2008 Ridley Turtles data, you will find a file called RidleyTurtles08.shp, that has a .shp extension.

  • Click once on RidleyTurtles08 to make the Ridley Turtle layer the active layer. Then click the Zoom to Active Layer Zoom to Full Extent button.

  • Save your project file.
    1. Choose File > Save As ...
      24 file save as
    2. Give the project a name like Ridley and save the new project in the Ridley Turtles folder.
      25 put in turtle folder

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Explore the Attribute Table of RidleyTurtle08

  • Open the Attribute Table of RidleyTurtle08 and inspect the fields in the table.
    1. Right-click(PC) or control-click(Mac) on the layer name RidleyTurtle08. Choose Attribute Table from the drop down menu.
      open attribute table 1
    2. The Attributes of RidleyTurtle08 table opens. Scroll across the table or stretch it to make it larger so you can view all the fields.
      Ridley_table

  • Sort the table in ascending order by MONTH.
  • Right-click(PC) or control-click(Mac) on the column header, MONTH. Then choose Sort Ascending.
    sorting attribute table
  • During what months was the data collected?
  • The data was collected in the months of August through December. This is the nesting period.
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Analyze the Data By Querying and Symbolizing

Perform a database query to find out where the turtles were by month

  • Where were the turtles in September? Write and execute a query to find out.
  • The query (MONTH = 9) highlights the positions of the turtles during the month of September.
    1. Click the Query Builder... Query builder button tool or select Tools > Query Builder.
      40 click query builder
    2. In the Query Builder window that opens, select the field MONTH by clicking once on it. Then click the "=" sign. Last choose the Value 9 by clicking once on it. You can also type in this equation (MONTH = 9) into the box in the middle of the window. Click Execute. Fifty-nine records are selected on the map.
      41 Month =9

  • Where were the turtles in October? Write and execute a query to find out.
  • (MONTH = 10)
  • Where were the turtles in November? Write and execute a query to find out.
  • (MONTH = 11)
  • Where were the turtles in December? Write and execute a query to find out.
  • (MONTH = 12)
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Symbolize the turtle data by month

  • Which turtles traveled where each month? To find out, symbolize the turtle tracking data using a different color for each month.
    1. Open the Properties window for the RidleyTurtle08 layer by right-clicking (Win) or control-clicking (Mac) the RidleyTurtle08 label in the Table of Contents. Choose Properties from the menu. Move the RidleyTurtle08 Properties window so you can see it and and the map at the same time. In the RidleyTurtle08 Properties window, choose a unique color for each month. Select the following options:

      • Draw features using: Unique Symbols
      • Field for values MONTH
      • Color Scheme Random
      • Style Square
      • Size 8
      • Click Apply
      symbolize by month

    2. The colors in the random color scheme may conflict with colors in the images on the map. Double click on the symbol color of a month to open the color swatches and select color choices that work better with the map.
      selecting choices

  • The 2008 olive ridley turtle data are now displayed so that each month of turtle paths is in a different color.
    Ridley_turtles_by_month
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Perform a database query to find out which turtles traveled where

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Symbolize the data by name

Five different olive ridley turtles, (Gloria, Showdancer, Carmen, Buttercup, and Esperanza) were tracked in 2008.

  • Which turtles traveled where? To find out, add a second turtle layer and symbolize each turtle's tracking data using a different color.
    1. To have a second turtle dataset to work with, click the Add Data add layer button button and navigate to the RidleyTurtleAE folder. Select the file RidleyTurtle08.shp, and click OK.
      Add ridley turtle shape again
    2. To open the Properties window for the RidleyTurtle08 layer, right-click (Win) or control-click (Mac) the RidleyTurtle08 label in the Table of Contents. Choose Properties from the menu.
      30 edit properties right click
    3. Move the RidleyTurtle08 Properties window so you can see it and and the map at the same time. In the RidleyTurtle08 Properties window, choose a unique color for each turtle's tracking data. Select the following options:

      • Draw features using: Unique Symbols
      • Field for values TurtleName
      • Color Scheme Minerals
      • Style Circle
      • Size 8
      • Click OK
      31 edit properies of turtles by name
  • The 2008 olive ridley turtle data are now displayed so that each turtle's path is in a different color.
    Ridley_turtles_by_turtle_name
  • Carefully observe the turtle tracks. Did all the turtles travel the same path? Describe their routes.
  • Buttercup headed out to sea and seems to have traveled the farthest. Gloria and Esperanza also swam out to sea. Shadowdancer and Carmen mostly stayed near the shore.
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Measure the Distances that Sea Turtles Travel

Olive ridley turtles are omnivores; they eat algae, small fish, crabs, shrimp, rock lobsters, jellyfish, and tunicates. They are pelagic, which means they spend most of their lives swimming and foraging in deep water. Olive ridleys have been observed thousands of miles offshore. They can dive to depths of 500 feet to forage on benthic, or bottom dwelling invertebrates. However, these adaptable turtles can also be found swimming in water nearly 10,000 feet deep. Scientists who study how these animals move use satellite images showing sea surface temperature and chlorophyll concentration to look for indicators of their movement.

  • How far, in total, did each of the turtles travel during the four months recorded on the map?
  • Which of the turtles traveled the farthest distance away from shore?
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Measure the distance traveled by a single turtle

  • Click on the Measure tool measure tool in the toolbar. From the drop-down menu choose miles as the unit for the measuring. Click, drag, click, drag, click, drag with the Measure tool as long as needed to use small segments to trace out the path of a turtle. The measure tool keeps a running total of the length of these segments.
    1. Click on the Measure tool measure tool in the toolbar. From the drop-down menu choose miles as the unit for the measuring.
      33 measure drop down
    2. Click, drag, click, drag, click, drag with the Measure tool as long as needed to use small segments to trace out the path of a turtle. The measure tool keeps a running total of the length of these segments.
      Esperanza total

    In total, Esperanza traveled 884 miles.
  • When you have finished measuring the path of a turtle, click on the Measure tool measure tool in the toolbar. From the drop-down menu choose Clear Measure Tools.
  • Use the Measure tool to trace out the path of each turtle and find out how far each one traveled. After measuring each path, be sure to choose Clear Measure Tools.
  • Buttercup traveled 1318 miles.
    Carmen traveled 205 miles.
    Esperanza traveled 884 miles.
    Gloria traveled 1056 miles.
    Showdancer traveled 518 miles.
    These measurements are approximate as they are based on "tracing" out the path by hand, with indication of order of the travels. Your numbers may differ.
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Measure the distance from the shore to the farthest point from land that a turtle travels

  • Click on the Measure tool measure tool in the toolbar. From the drop-down menu choose miles as the unit for the measuring. Click and drag a line from the shore to the point farthest from land. The line should be perpendicular to the shore. Notice the measurement in the upper left corner of the map window. After measuring each straight line distance, be sure to choose Clear Measure Tools.
    1. Click on the Measure tool measure tool in the toolbar. From the drop-down menu choose miles as the unit for the measuring.
      33 measure drop down
    2. Click and drag a line from the shore to the point farthest from land. The line should be perpendicular to the shore. Notice the measurement in the upper left corner of the map window.
      35 measuring distance from shore

  • What is the farthest distance that any of the turtles traveled in a straight line from the shore?
    The farthest that any of the turtles traveled from the shore as measured in a straight line perpendicular to the shore was 771 miles for Esperanza.

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Add Monthly Images of Sea Surface Temperature and Chlorophyll to Explore Patterns

Chlorophyll is a proxy data set for phytoplankton, which is at the base of the food web. Olive ridley turtles are pelagic, spending most of their lives swimming in nutrient rich waters where there is upwelling. They are opportunistic feeders and primarily consume shrimp, small fish, and jellyfish.

  • Click the Add Data add layer button button and navigate to the RidleyTurtlesAE folder. Add the three other months (October, November, December) of sea surface temperature and chlorophyll images to the project.
  • Turn layers on and off to investigate the relationship between the turtles' travels and these images.

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Learn More About the Threats Facing Olive Ridley Turtles Today

The historic olive ridley fishery in Mexico was, at one time, the largest turtle fishery in the world. Today, turtles are accidentally caught in shrimp trawls, longlines and gill nets. Once caught, they drown because they cannot resurface to breathe. Sea turtles also confuse trash, especially plastics such as shopping bags and even balloons, for food and die due to starvation and choking.

Today, due to several factors, the olive ridley turtle is listed as endangered by the International Union for Conservation of Nature (IUCN). These factors include the harvesting and degradation of nesting sites. Once common in Mexico, only one nesting site remains. All over the world olive ridley turtles are at risk due to the harvesting of their eggs. Additionally, tens of thousands of olive ridleys and other turtles are accidentally caught in fishing nets, purse seines, and trawls. Conservation efforts are now being implemented for the olive ridley and other turtles. These efforts include turtle excluder devices (TEDs) on fishing gear. Around the world, conservation of turtles is an important topic and priority for fishers and other concerned citizens.

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Resources

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