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

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Launch AEJEE and Add Data Layers

AEJEE_logo

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:

  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

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.

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Explore the Attribute Table of RidleyTurtle08

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Analyze the Data By Querying and Symbolizing

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

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Symbolize the turtle data 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.

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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.

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Measure the distance traveled by a single turtle

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Measure the distance from the shore to the farthest point from land that a turtle travels

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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.

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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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