The Use of Geographic Information
Systems (GIS) in Marine Turtle Research
|
The Use of Geographic Information
Systems (GIS) in Marine Turtle Research
|
|
There are five living genera and six species of
marine turtle in the world (2). Of these six species, five (loggerhead,
green, hawksbill, olive and kemp's ridley, and leatherback) inhabit North
American waters. All five of these species are now protected  under
the Endangered Species Act due to a variety of causes world (2). All sea
turtles exhibit a variety of life history  characteristics
that make them particularly susceptible to human disturbance. Marine turtles
grow slowly, breed infrequently, undertake long migrations, and utilize
many habitats that expose them to human-induced mortality (2). Most detrimental
to marine turtle populations have been harvest of mature turtles and turtle
eggs for food, destruction of feeding and nesting grounds, and mortality
as bycatch in nets and long-lines aimed at other species (7). Faced with
so many threats, marine turtles have been the focus of prolonged research
efforts aimed at reducing mortality and better understanding their life
histories. Recently, Geographic Information Systems (GIs) along with a variety
of remote-sensing techniques have revolutionized sea turtle research. The
use of GIs in marine turtle research can basically be split up into three
categories: 1) using GIs and remote sensing to track long-distance movement
of turtles and establish population dynamics within species, 2) Tracking
short-distance movements of turtles to analyze key habitat areas and evaluate
causes of turtle mortality, 3) Analyzing turtle habitat to implement sound
conservation measures. |
| Using GIs and remote sensing to track long distance movements
of marine turtles: Until recently, long-distance movements of marine turtles and large scale population structure of turtle species remained unknown. It was known that different regions hosted different age structures of turtles and that certain nesting beaches served turtles from large geographic areas, but the dynamics of turtle populations and even which areas represent separate populations remained unclear. The development of sophisticated remote sensing equipment in recent years has allowed researchers to begin unraveling the mysteries of marine turtle migration. Particularly important has been the use of satellite transmitters in tracking turtles over long distances.  Researchers
across the globe have tagged turtles of several species in an effort to
discover turtle migration patterns and delineate populations. In these studies
a tag is attached to the
shell of the turtle and the turtle is released. Each time the turtle surfaces,
the tag sends a signal to satellites in orbit around the earth. The signal
conveys data on position, position accuracy, dive frequency and duration,
and temperature (1).
When this data is entered into a GIs the path of the turtle can befollowed
over long periods of time (in some cases more than a year). Although these
technologies are still young and expensive, they have already yielded some
very enlightening results. For example, Nichols et al. tracked a captive
raised adult loggerhead turtle over 11,500 km from Santa Rosaliita, Baja
California, Mexico to Sendai Bay, Japan, confirming that loggerhead turtles
in the eastern and western Pacific constitute one population (6). This study
also allowed the prediction of a loggerhead migration corridor between 25
degrees and 30 degrees N in the pacific (6). Similarly, a team in Bermuda
tracked a young adult green turtle from nursery grounds in Bermuda across
the Caribbean to the Dominican Republic and Cuba, proving that green turtles
in Bermuda are part of a larger Caribbean population (1).
Other studies have focused on determining the mechanisms of sea turtle navigation.
A study by Papi et al., for example tracked, by satellite, control turtles
and turtles that were fitted with magnets designed to obscure the earth's
magnetic field on migration between Brazil and the Ascension Islands (8).
They found no significant differences between control and experimental turtles,
leaving the mechanisms of turtle navigation a mystery (8). (Pictures from
NMSF-Galveston Laboratory http://galveston.ssp.nmfs.gov/galv/turtles/tracking.htm
(permission pending). |
|
 |
 |
| Track of a Kemp's Ridley off the Gulf Coast of Texas tracked by satellite (http://galveston.ssp.nmfs.gov/galv/turtles/tracking.htm permission pending) | Track of a "Bermudiana" a Green Turtle tracked from Bermuda to the Caribbean ( http://www.cccturtle.org/bermuda/discoveries.htm permission pending) |
| Short-distance tracking of turtles to determine habitat
use and identify areas in need of protection: In efforts to minimize marine turtle mortality and protect areas that are especially important to turtle biology it is necessary to study turtle movements on a small scale. This  research
has typically been carried out using Global Positioning Systems (GPS) remote
sensing equipment. Turtles are tagged either with a buoy or with  a
radio tag. The turtle is then followed by boat plane and its location marked
at specific time intervals using a handheld GPS unit , (5,
7). The NMFS-Galveston Laboratory has even set up a series of ground station
receivers that allow for triangulation of a turtle's position when weather
does not allow boat or air travel (5).
The data gathered in this type of study is used to identify specific areas
where turtles spend large amounts of time. These areas can then be targeted
for protection. One such study has been started in Magdalena Bay, Baja California
to determine key feeding areas for juvenile green turtles in the bay (7).
By following individual turtles for periods of up to 72 hours, many key
habitat areas have been identified and are now targeted for a community-based
marine turtle reserve (7). Similar studies have been performed along the
Gulf Coast of Texas and in Bermuda  (9,
5)
. (Pictures from NMSF-Galveston Laboratory (permission pending) http://galveston.ssp.nmfs.gov/galv/turtles/tracking.htm.
|
| Analyzing habitat in order to implement sound conservation
measures: There is much to be learned about marine habitats and how the affect the lives of turtles. GIs has been invaluable in viewing this kind of data and analyzing it in relation to sea turtle abundance and movement. The uses of these types of technology are so wide and varied that imagination is virtually the only limiting factor. Some studies have focused on analyzing ocean and climatic conditions and how that effects turtle movement (5). Another, study by researchers working at the Duke University Marine Laboratory in North Carolina used GIs to plot shrimp fishing intensity and marine turtle abundance along the Gulf Coast of the United States. When analyzed together these data was used to pinpoint areas where fisheries closures would be most beneficial as well as areas that should be targeted for use of turtle excluder devices (TED's) in shrimp nets (4). |
|
|
A)
 |
B)
 |
|
C)
 |
|
|
GIs representations of A) Shrimping
Intensity along the Gulf Coast of the United States B) Turtle Abundance
C) Shrimping Intensity and Turtle Abundance. With Permission form C. J.
McDaniel http://www.consecol.org/vol4/iss1/art15.
|
|
| On a larger scale, the Convention of Migratory Species (CSM) has used data from many sources to compile an interactive GIs map of marine turtle nesting sites in the Indian Ocean (3). This map is an amazing tool available to the public on line and even allows the overlaying of protected areas, coral reefs, and mangrove areas. This is an example of how GIs will allow the sharing of data between researchers to better understand species like marine turtles that utilize huge geographic areas over the course of their lives. | |
 |
 |
|
GIs view of Sea turtle nesting areas in the Indian Ocean.
From http://www.wcmc.org.uk/marine/mturtle/instructions.htm
|
Close up view of Green Turtle nesting areas in a small
section of Southeast Asia, showing protected areas (in red)
From http://www.wcmc.org.uk/marine/mturtle/instructions.htm
|
Citations:
E-Mail me | Imaging the Earth Home | Reptile and Amphibian Conservation