The goal of the Bermuda
Turtle Project is, "to promote the conservation of marine turtles
through research and education". The project team has made notable
progress to date and has exciting plans for expanding research and
The Bermuda Turtle Project has assembled important data sets on size
and maturity status, growth rates, sex ratios, residency, site
fidelity, genetic diversity, and movement patterns in immature green
turtles in Bermuda waters. We have assembled similar, but much
smaller, data sets for Bermuda hawksbills.
Our findings show that Bermuda serves as a year-round habitat for
immature green turtles and hawksbills, providing a 'developmental'
feeding ground for nesting beach populations that are located mostly in the Caribbean,
but may exist as far away as Cyprus in the Mediterranean.
Our data show that green turtles arrive at Bermuda at a size of
about 25 centimeters (10 inches) and leave by the time they have grown
to approximately 75 centimeters (30 inches). Stranding records show a similar distribution of sizes, with a very
small number of turtles that are smaller than the minimu size of
turtles caught in the net.
Green turtles are about the size of a silver dollar when they hatch,
and take about thirty to fifty years to reach maturity.
Thus, it is easy to see how a project such as this one, which has been
gathering data since 1968, is so valuable. It takes years to collect
enough data to understand life history patterns.
The gaps at either end of the size distribution graph for green
turtles in Bermuda represent the epipelagic phase that
follows hatching, previously known as the 'lost year,' and
the large but still immature sub-adults that have departed to the
adult resident habitat.
During the years 1990
through 1992, most turtles captured by the project were laparoscoped.
In this procedure, a small incision is made through the body wall of
the turtle and the gonads are viewed using a surgical scope to
determine sex and maturity status. By examining 138 immature turtles, we were able to establish that none were mature
and to calibrate a hormone assay that allows us to determine a green
turtle's gender from a blood sample.
Caldwell and Mowbray wrote in 1954 that green turtles in Bermuda were
probably itinerant and were delivered to the island annually by the
Gulf Stream. By sampling year round, we were able to show
that green turtles are year round residents. We actually found a density in January matching, if not surpassing, that of the
summer months. This is possible because Bermuda waters do not drop drastically in
temperature during winter months. Bermuda
waters stay as warm as those of the SE coast of Florida.
Information from local recaptures has shown that young green turtles
in Bermuda establish specific feeding areas. Even if displaced, they
usually return to these particular sites and may stay there for many
The greatest number of times that a single individual turtle has
been captured in Bermufa is seven. This turtle was captured on the same grass flat
each time. The longest period of time over
which we know that an individual has remained in Bermuda waters is 14
years. Based on the size at first capture, these 14-year residents were probably in Bermuda for a few
years before their first capture and probably stayed a few more
years before departing. So, we expect a maximum residency time of about
twenty years for green turtles.
Using a Geographic Information System (GIS) we can visualize
patterns of habitat use that may be related to seasonality, turtle
size, sex, and other biological and physical characteristics of
the habitat. Analysis of turtle distribution data with GIS will be of
great benefit to management authorities in identifying critical habitat.
Blood samples are taken
from each turtle to determine gender and genetic identity. Serum samples are sent to Dr. David Owens at the Grice
Marine Laboratory, College of Charleston, SC, where the amount of
testosterone in the blood is determined. These data are used to
determine the sex of immature animals. A second blood sample is preserved in a
buffer which stablizes the DNA so that it can be used to determine genetic identity.
We have been compilng and analyzing genetic sequence
data from Bermuda turtles since 1996. Our studies show that Bermuda green turtles
match gene sequences of green turtle populations from Florida,
Mexico, Costa Rica, Cuba, Aves Island (near Dominica), Suriname, Cyprus,
and either Ascension, Brazil or Guinea Bisseau in the South Atlantic.
As of 2005, 88 green turtles caught and tagged in Bermuda have been
found overseas in Venezuela, Colombia, Nicaragua, Panama, Cuba, the
Dominican Republic, Saint Lucia, the U.S. and Grenada. This information, along with genetic results, highlights the regional
significance of Bermuda to the green turtle. It also confirms the need
for international cooperation in sea turtle conservation. Unless
green turtles are protected on the nesting beaches and in their adult
Bermuda may lose its feeding aggregation, in spite of efforts to
in Bermuda waters. To date, the project has recorded only one
recapture of a hawksbill turtle. The animal was captured with a spear
gun off the east coast of Grenada eleven years after being tagged in
Between 1996 and 2008, we deployed eight satellite transmitters
attached to Bermuda green turtles. These transmitters transmit
messages to satellites when the turtles surface to breathe. Data
(latitude, longitude, location accuracy, dive frequency and duration,
and temperature) are uploaded to the satellite. Positions of the turtle
are plotted using the Geographic Information System developed for the
project. One of these transmitters sent data for fifteen months. Most
positions recorded were centered on the capture area, and it is
believed that the turtle did not travel any significant distance.
However, one of the seven turtles fitted with a transmitter did
make a significant journey.
In August 1998, a 78.6 - cm green turtle carrying a satellite
transmitter departed the Bermuda Platform about two weeks after
attachment. We were able to record her remarkable journey of
approximately 1,500 kilometers (932 miles) which took her south to
the Dominican Republic and then west to Cuba. This turtle, named
"Bermudiana," was originally captured on August 5th with a net on the
seagrass flats off the northwestern end of Bermuda. Location and dive
data were received for the turtle on a daily basis. The turtle was just
north of the coast of the Dominican Republic as Hurricane Georges
passed by, but there were no observable effects. Several days later,
however, transmissions changed dramatically and eventually stopped. We
believe that Bermudiana was captured off the eastern tip of Cuba, near
the town of Baracoa (map shown).
Starting in 2011, we attached transmitters that can take GPS location data, in addition to standard Argos data. These will allow a much more precise understanding of how young green turtles use Bermuda waters. Results from these transmitters can be seen here.
The Bermuda Turtle Project serves as a useful vehicle for public
outreach and education. In addition to the many volunteers
who join the field efforts each year, teachers, school classes, and
eco-tour groups are educated about the plight of the endangered green
turtle through slide shows and lectures. Guest scientists
contribute nearly annually to the project, the associated course, and
to public outreach via lectures. The project has benefitted greatly by
visits from Robert George, Tierry Work, Brendan Godley, David Owens,
Marydele Donnelly and Robert van Dam.
The Bermuda Turtle Project hosts an International Course on the Biology and Conservation of Sea Turtles
each year. The two-week course consists of lectures, class discussions
of assigned readings, a necropsy session, and extensive field work
capturing immature green turtles.
Some of the basic findings of the project appear in a Bulletin of the American Museum of
Natural History. This publication is available online at: http://digitallibrary.amnh.org/dspace/handle/2246/6126
The Bermuda Turtle Project looks forward to sharing our new discoveries with you!
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