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

Week 12: Comparing Geospatial Tools

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Exploring Ocean Data with ArcGIS

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 the link below to download the zipped file of data and images.
    RidleyTurtlesAM.zip (Zip Archive 5.7MB May7 10)
  • Unzip the file. A folder called RidleyTurtlesAM will be created.
  • Move the entire RidleyTurtlesAM folder into the Data folder inside the ArcGIS folder. (Path: c://eyesintheski2/week12/RidleyTurtlesAM)

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Launch ArcGIS ArcMap and Add Data Layers

Shortcut1
  • Launch ArcMap by double-clicking its icon on your desktop or by clicking its icon in the Launch Bar.
  • To add a September 2008 Sea Surface Temperature image, click the Add Data 5205 Add Data Button button. Navigate to the RidleyTurtlesAM folder. Click once on Sept2008SeaSurf.TIF to select the image. Then click Add.
  • Repeat the procedure to add the Sept2008Chlorophyll.TIF image.
  • Uncheck the Chlorophyll layer to turn it off and make sure that the 2008 Sea Surface Temperature layer added propertly. Then turn the Chlorophyll layer back on.
  • Last, click the Add Data 5205 Add Data Button button and navigate to the World folder. Click once on country06.shp to select it. Then click Add.
    1. Click the Add Data 5205 Add Data Button button.
      01 Add Data Interface
    2. Navigate to the Week12 folder.
      02 Navigate to Tif
    3. Navigate to the RidleyTurtlesAM folder.
      04 Navigate RidleyAM Folder
    4. Click once on Sept2008SeaSurf.TIF to select the image. Then click Add.
      5 SeaSurf Temp
    5. Repeat the procedure to add the Sept2008Chlorophyll.TIF image.
      6 Chlorophyll Image
    6. Both images are now in the project. Turn the Sept2008Chlorophyll.TIF image on and off to compare the Sept2008SeaSurf.TIF image with the Sept2008Chlorophyll.TIF image.
      7 SeaSurf Temp On
    7. Click the Add Data 5205 Add Data Button button and navigate to the RidleyTurtleAM folder.
      9 Navigate to Ridley Turtle Data
    8. Click once to select cntries07.shp. Then click Add.
      8 Countries Shapefile

  • Edit the properties of the cntries07.shp to display it with a light gray fill and a dark gray outline.
    1. Right-click on the name of the layer (cntries07.shp) and select Symbology tab and then click on Symbol.
      11 Symbology Symbol
    2. Choose Fill Color to be Gray 10%.
      1 Choose 10 gray
    3. Choose Outline Color) to be Gray 60%. Click OK and then OK again.
      13 Outline Color Gray 60

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


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Add X/Y Data for Ridley Sea Turtles

Add ridley turtle data from 2008

To map the 2008 Ridley Turtle tracks using Longitude and Latitude coordinates, choose Tools > Add XY Data. The Add XY window opens. Click the Browse 15 Browse Button button to navigate to the file named RidleyTurtles08.csv. (Path: c://eyesinthesky2/week12/RidleyTurtlesAM/RidleyTurtles08.csv). Choose Longitude for the X Field and Latitude for the Y Field. Draw the XY points using symbols that are White Circles with a point size of 5. The options in the Add XY window are as follows:

  • Table: c://eyesinthesky2/week12/RidleyTurtlesAM/RidleyTurtles08.csv
  • X field: Longitude
  • Y field: Latitude
  • The Output Directory defaults to the current folder that you opened the Turtle file from. Accept this default.
  • Click OK.
  1. Select Tools > Add XY.
    16 Tools add XY
  2. The datasets are within the RidleyTurtlesAM data folder. Click the Browse 15 Browse Button button.
    17 Tools Add XY Window
  3. Navigate to the RidleyTurtlesAM data folder.
    18 Navigate to Ridleyturtles 08
  4. Click once on the file named RidleyTurtles08.csv to select it. Then click Add.
    19 Open Ridley Turtles
  5. In the Add XY Data window define which column in the data base contains the coordinates.
    • Table: Applications c://eyesinthesky2/week12/RidleyTurtlesAM/RidleyTurtles08.csv
    • Select X field: Longitude
    • Select Y field: Latitude
    • Click OK.
    • Click OK for Table Does Not Have Object – ID Field.
    • 20 Add XY Window

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Convert XY data to shapefile


To get full functionality from your XY points, it is necessary to convert your XY point layers to shapefiles. It is a simple two step process.
  • Right click on the RidleyTurtles08.csv Events layer. Click on Data > Export Data.
    21 DataExport Data
  • Navigate to project folder and give Ridley Turtle points a name and click Save.
    22 Name Shapefile
  • Click OK and click Yes to add exported data to your map as a layer.


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Symbolize by color

In the Properties window, click on the symbol button. In the Symbol Selector window, change the color of the turtles to Whitewith no outlines and size 5. Select the following options:

  • Draw features using: Single Symbol
  • Style Circle1
  • Color White
  • Size 5
  • Click OK and Click Apply
  1. Click on the symbol dot below the RidleyTurtles08 layer name in the Table of Contents.
    23 Turtle Dot
  2. When the Symbol Selector window opens, click on the black Circle1 symbol.
    24 Symbol Selector Window
  3. Under Options, click on Color and change the color to White by selecting it from the Color Palette.
    25 Change Color Under Options, click on Size and change the size to 5.
    26 Change Size

  • The 2008 Ridley Turtles will now be displayed on the map as white dots.
    27 Map with White Turtle Dots
  • Note: If you enter the X and Y fields incorrectly, the data will either not project or will project incorrectly. Also, remember that when ArcGIS imports and projects a tabular dataset onto a map, it is NOT creating a shapefile. Those XY coordinates are just graphic dots and you must convert them to a shapefile to be able to perform different analytical operations on those dots. Once you convert the dots to a 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.

  • Right click once on RidleyTurtles08 layer and then click on Zoom to Layer. Make sure to turn off the Sept2008Clorophyll layer.

  • Save your project file.
    1. Choose File > Save As ...
      29 File Save As
    2. Give the project a name like Ridley and save the new project in the Ridley Turtles folder.
      30 File Save Give Name

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    Explore the Attribute Table of RidleyTurtle08

    • Open the Attribute Table of RidleyTurtles08 and inspect the fields in the table.
      1. Right-click on the layer name RidleyTurtles08. Choose Attribute Table from the drop down menu.
        31 Open Att Table
      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.
        32 Att Table Stretched

    • Sort the table in ascending order by MONTH.
    • Right-click on the column header, MONTH. Then choose Sort Ascending.
      33 Sort by Month
    • During what months was the data collected?
    • The data was collected in the months of August through December. This is the nesting period. Close the Attribute Table.
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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 Selection>Select by Attributes.
        34 Select byAttribute
      2. In the Select by Attributes window that opens, select the field MONTH by double clicking on it. Then click the "=" sign. Last choose Add All Values and double click on 9. You can also type in this equation (MONTH = 9) into the box in the middle of the window. Click OK. Open the Attribute Table to view the fifty-nine records that are selected on the map.
        35 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 the RidleyTurtle08 label in the Table of Contents. Choose Properties from the menu. In the RidleyTurtle08 Properties window, choose a unique color for each month. Select the following options:

        • Draw features using: Categories = Unique Values
        • Field for values MONTH
        • Color Scheme Random
        • Style Default
        • Size Default
        • Click Ok
        36 Unique by Month

      2. The colors in the random color scheme may conflict with colors in the images on the map. You may choose to double click on the symbol color of a month to open the color swatches and select color choices that work better with the map.
        37 Change Ind. Symbols

    • The 2008 olive ridley turtle data are now displayed so that each month of turtle paths is in a different color.
      38 Turtle Map 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 turtle name

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

    • Which turtles traveled where? To find out, make a copy of the existing turtle layer to create 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, right click the RidleyTurtles08 layer in the Table of Contents and click on the Copy menu option.
        41 Right Click Copy
      2. Click on the Paste button [thumbnail 20942 24.
        43 Two Layers
      3. To open the Properties window for the RidleyTurtle08 layer, right-click the RidleyTurtle08 layer in the Table of Contents. Choose Properties from the menu.
        44 Travel by Turtle
      4. In the RidleyTurtle08 Properties window, choose a unique color for each turtle's tracking data. Select the following options:

        • Draw features using: Categories = Unique Values
        • Field for values TurtleName
        • Color Scheme Random
        • Style Default
        • Size Default
        • Click Ok
        50
    • The 2008 olive ridley turtle data are now displayed so that each turtle's path is in a different color.
      45 Travels
    • 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 46 Measure Tool in the toolbar. From the drop-down menu choose miles as the unit for the measuring.
        47 Measure Miles
      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. When you are finished tracing the line, double click the Measure tool.
        48 Complete Measure

      In total, Esperanza traveled 889 miles.
    • Use the Measure tool to trace out the path of each turtle and find out how far each one traveled.
    • Buttercup traveled 1120 miles.
      Carmen traveled 106 miles.
      Esperanza traveled 884 miles.
      Gloria traveled 1044 miles.
      Showdancer traveled 524 miles.
      These measurements are approximate as they are based on "tracing" out the path by hand. 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 46 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.
      1. Click on the Measure tool 46 Measure Tool in the toolbar. From the drop-down menu choose miles as the unit for the measuring.
        47 Measure Miles
      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.
        49 Perpendicular Measure

    • 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 854 miles for Buttercup.

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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 5205 Add Data Button button and navigate to the RidleyTurtlesAM 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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