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Gaining an understanding of the movements of marine turtles is far from
a simple task: turtles spend most of their life at sea below the surface
and tend to migrate long distances among disparate developmental, breeding
and adult feeding habitats. For decades the main tool used to gain insights
into the distribution and migration in sea turtles was flipper tagging,
with important insights gained. However, recent technical advancements
and the use of satellite transmitters have greatly increased our knowledge
of marine turtle migrations.
| Essentially these
are radio transmitters that transmit a signal that that can be detected
by polar orbiting satellites. Depending largely on the number of signals
received from an individual tag by a satellite in any given overpass,
locations with different levels of accuracy can be assigned. In addition
to generating positional information, other data from onboard sensors
can also be transmitted, giving information of a range of parameters
such as temperature, depth and dive profiles as well as swim speed.
Because transmitters can be attached to turtles and the data collected
can be recovered by satellite even if the turtle swims hundreds or
thousands of kilometers away from where it was released, the technique
holds great potential for unlocking many secrets of marine turtle
behaviour and ecology. |
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At the current time, all satellite tags that are commercially available
function through the ARGOS system. For a complete overview over this system,
you are referred to the websites of:
Using satellite tags it has been possible to detail the post-reproductive
migration routes of adult females and males, and to ascertain the location
and use of foraging grounds in both neritic and pelagic areas by adults
and juvenile sea turtles. Satellite transmitters yield data that could
not otherwise be obtained. Nevertheless, there are two main disadvantages
associated with them: 1. their limited lifespan (most satellite tag deployments,
with exceptions, have yielded data for less than one year); 2. their cost
(each tag including satellite time is likely to cost more than US$3000
USD, although if you want to collect more kinds of information with the
tag, it can cost more than US$6000 per animal). An additional point that
must always be considered is the possibility of any attached device might
affect the behaviour of the animal being studied. For instance, it could
be that large satellite tags might increase hydrodynamic drag of the turtle
that in turn could affect its migration speed and route. Nevertheless,
in most cases those sea turtles that receive satellite tags are large
animals and technological advances have resulted in reasonable satellite
tags that are <1% of the bodyweight of the turtle and have a relatively
little hydrodynamic impact. An additional point that should be borne in mind is that the data generated
by satellite tags are exciting and have great potential for raising awareness
and increased education. SEATURTLE.ORG is committed to making the most
of such projects and in collaboration with the MTRG has designed a tracking
website which hosts near real-time tracking data from a number of turtle
projects.
If your aim is to locate the migratory routes and foraging areas of adults
after they have left the breeding area then undoubtedly satellite tracking
is the technique for you. However, given the power and design of the satellite
tags that are currently available, this might not be best technique for
describing fine short-range movements, although please note that useful
short-range data have been gathered using satellite tracking of juvenile
turtles (e.g., see Polovina et al 2000, Godley et al 2003 in the tagging
bibliography). Another consideration is where the turtles will be during
the study. At the current time, satellite coverage over the equator is
limited relative to more extreme latitudes. As a result, you may get fewer
reliable locations from satellite transmitters on turtles that remain
in the tropical waters close to the equator. It is hoped that in the future
more satellites will be available to increase coverage across the globe.
Overall, you should be prepared to accept that some location data collected
are not very precise or accurate. As always, care must be taken when interpreting
the data.
Assuming the technique is for you and you have the available resources,
the two main steps are:
- Setting up an ARGOS program through ARGOS.
This is carried out through CLS (http://www.cls.fr/html/argos/welcome_en.html)
or, in North America, Argos Inc (http://www.argosinc.com/).
Some nations, such as UK, have a co-operative buying group for satellite
time where different research organizations combine their bids for the
coming year that allows satellite time to be obtained at reduced prices.
Contact CLS or Argos to enquire if this is a possibility for you.
- Selecting and buying hardware.
Only a certain number of suppliers are licensed to produce satellite
transmitters. These are listed at (http://www.argosinc.com/documents/list_manufs.doc).
Only a subset of these suppliers produces equipment suitable for attachment
to marine turtles. It is recommended that you look at the manufacturers'
websites, read the scientific literature and communicate with those
who have already used different kinds of satellite tags before you conduct
your study. Note that manufacturers usually ask to be paid in full before
building the satellite tags and, depending on current orders, there
is often a significant delay between when you place your order and when
you receive your satellite tags. Be sure to plan carefully and budget
enough time for delays when ordering!
Most manufacturers supply a range of options that vary in price. The
prices are constantly changing but in general, cost increases with battery
life and with complexity of data collected and transmitted. There is
undoubtedly considerable variation in the performance of tags depending
on make and model used, size and species of turtles, location of deployment,
season and attachment method. However, attachment methods, transmitter
design and satellite sensitivity all have been changing simultaneously.
These factors compounded by the small numbers deployed in different
projects make it difficult to rigorously compare among the different
manufacturers and models. There is probably a role for all available
transmitter models, depending on the questions being asked, the data
required and the budget in hand. For example, if you simply need to
know where turtles are going then it makes more sense to have a larger
sample size of individuals and buy basic (and cheaper) Sirtrack or Telonics
units. If however, you are interested in diving behaviour then you will
need to consider more advanced (and more expensive) Telonics, Wildlife
Computers or Sea Mammal Research Unit models.
The table below briefly outlines some of the benefits and drawbacks
of the capabilities of the product ranges of the main manufacturers
that have been used to date on sea turtles. If you have points that
you feel are of particular concern then let us know at tagging@seaturtle.org
and we will post them in our TIPS section.
| Manufacturer |
Main benefits |
Main drawbacks |
| Sea Mammal Research Unit, UK |
Unsurpassed data collection on individual dive profiles, swim
speed. Resilient antenna. |
Most expensive. Moderately large and only suitable for larger
turtles. Only one model and no custom designs of hardware. |
| Sirtrack, New Zealand |
Relatively inexpensive. Range of sizes. Resilient antenna. Streamlined
molds available. |
Only location with no data collection regarding diving. |
| Telonics, USA |
Range of sizes. Data collection options including dive statistics
and temperature on more expensive models. |
Moderately expensive for all but the most basic units. |
| Wildlife Computers, USA |
Range of sizes, Data collection options including dive statistics
and temperature. Self programmable options in data collection. |
Moderately expensive. |
Above all, be sure to contact the manufacturers directly to discuss
your project needs and objectives. The technicians of each company have
been helpful and willing to modify their equipment to meet the concerns
of different groups working on sea turtles.
These manufacturers all have websites available on the Internet:
In addition, the following sea turtle workers have experiences with
the equipment of the different manufacturers and may be contacted for
advice:
Sea Mammal Research Unit:
Sirtrack:
- J. Frazier, Smithsonian Institution, USA <kurma@shentel.net>
- B.Godley/A.Broderick, MTRG, University of Exeter in Cornwall, UK
<mtrg@seaturtle.org>
- K Pendoley, Perth, Australia <pendoley@newton.dialix.com.au>
- Alan Rees, Archelon, Greece <alan@archelon.gr>
- J. Shepherd, James Cook University, Australia <James.Sheppard@jcu.edu.au>
Telonics:
- G. Balazs, National Marine Fisheries Service, Hawaii, USA <gbalazs@honlab.nmfs.hawaii.edu>
- Luis Cardona, University of Barcelona, Spain <carreras@ub.edu>
- S. Eckert, Duke University Nicholas School of the Environment and
Earth Sciences Marine Laboratory, USA <seckert@widecast.org>
- B.Godley/A.Broderick, MTRG, University of Exeter in Cornwall, UK
<mtrg@seaturtle.org>
- P.Luschi, University of Pisa, Italy <luschi@discau.unipi.it>
- W.J. Nichols, Wildcoast, USA <wjnichols@wildcoast.net>
- J. Shepherd, James Cook University, Australia <James.Sheppard@jcu.edu.au>
Wildlife Computers:
-
To have a duty cycle or not?
Once you have decided which manufacturer purchase from, most transmitters
have a series of programming options. You can consult with the technical
help desk of the manufacturer for advice about what programming options
are best suited to your needs. One consideration is determining the
power cycle or duty cycle of the transmitter. Transmitters come with
salt-water switches that conserve the battery life by ensuring that
transmissions are made only when the turtle is at the water surface.
However, you can conserve the battery power even more by programming
some transmitters to turn off during certain times e.g. 24 hours on,
48 hours off. Although these cycles have the capacity to increase the
longevity of the tag, they also reduce the rate of receipt of locations
and/or successful transmissions of data. Note that many deployments
fail before the end of battery life of the transmitter, therefore in
some cases it may be beneficial to program the satellite tag to maximize
transmission at the cost of the battery life. Overall, each project
(and its objectives) is different, so it is up to you to decide whether
reducing the resolution of data collection is worth the chance of increased
duration of monitoring.
-
Restrain your subject animal
 Once
you have decided to attach a satellite tag to a turtle, you must have
some way of restraining a turtle. If you are working on juvenile sea
turtles, you can probably move them to a large plastic box or tub that
will keep them from moving around too much. If you are working outside
during the day, be sure to provide some shade so that the turtle does
not overheat. For nesting females, you should wait until after the turtle
has finished laying her eggs. Some workers have attached transmitters
to green turtles and leatherback turtles without additional restraint
during the normal nest covering/descent behaviour but it is probably
best to restrain the turtle's movement in some way.  One
way of doing this is by assembling interlinking wooden barriers on all
four sides around her, forming an uncovered "box." Once the box is secured,
it is easy to reach over the top of the box to work on the carapace
of the turtle, in order to attach the satellite tag. Once you are finished,
the sides of the box are easily lifted and the turtle can continue on
her way to the ocean. See photographs from satellite tracking projects
at Bald Head Island and Cayman Islands.
- Attach the satellite transmitter to the turtle.
There are a variety of ways you can attach satellite transmitters to
turtles. The methods used to date have include gluing them directly
to the carapace and the horny plates covering the head, joining them
by tether to a small hole through the carapace, attaching them first
to a harness that is then fitted around the turtle, or by attaching
the transmitter first to a plate which is fastened to the tissue of
the turtle using orthopedic screws. Please note that in some countries
or states, there may be specific rules related to attachment of transmitters
to sea turtles. Be sure to check with the appropriate regulatory agencies
in your area to ensure that you are using an acceptable method.
- Attachment by gluing. Usually this is done by two-part epoxy,
fiberglass resin/bondo, or a combination of the two. Before you use
any attachment method, be sure to test the amount of heat that is produced
by the epoxy or fiberglass resin. If the heat of the curing glue is
too hot for your hand, it is probably too hot for the turtle. The carapace
of the turtle must be cleaned and dried in advance of attachment. You
should gently remove any barnacles or other epibionts with a scraper
or pliers. Then clean the entire carapace with a soapy solution and
steel wool (e.g. Brillo Pads). Once you have thoroughly cleaned the
carapace with the steel wool and soap, rinse with water (either fresh
or seawater), dry with towels, and then lightly sand the carapace with
medium grade sandpaper. This sanding will further clean the carapace
and gently score the surface of the carapace. After sanding, you should
rinse off the carapace with water, dry with towels and then wipe again
with acetone to ensure the carapace is thoroughly clean, dry and ready
to receive the satellite transmitter. Remember to cover the turtle's
head lightly with a towel to protect it from accidental splashes of
soap or acetone. In some situations the turtle's carapace may be heavily
fouled, and it may be necessary to repeat each step several times. The
specific details about gluing the transmitter on the carapace vary among
different projects. To learn how to attach a satellite tag, the best
thing to do is to visit another project where transmitters are being
attached, to gain firsthand experience. There is also a detailed example
of attachment by epoxy available here (Hard Shell Sea Turtle PTT Attachment Protocol).
The following is a list of different supplies and suppliers that might
be used when gluing a satellite tag to a turtle carapace, based on that
supplied by Dean Bagley of University of Central Florida. It is likely
that the same products or analogues will be available where you are
working:
- PowerFast is a two-part epoxy that has worked well in satellite
tag attachment. It comes in two varieties: Fastset (it cures faster)
or Slowset (it cures more slowly). If you use Fastset, you should
add the epoxy sequentially in thin layers, allowing each layer to
cure (dry) first before adding more layers, otherwise the curing
may generate too much heat. It is available here: (http://www.toolfetch.com/tools/index.html).
- Elastomer can be used as a base to "seat" the satellite tag snugly
against the carapace before the epoxy and/or fiberglass resin/bondo
are applied. One distributor is Sammons-Preston Rolyan, P.O. Box
93040; Chicago, IL 60673-8005. (630) 226-1300 (http://www.sammonspreston.com/)
- Silmar 249 Surfboard resin and catalyst (for fiberglass cloth)
if often used for attaching satellite tags, and is available here
(http://www.shopmaninc.com/polyesters.html)
- Fiberglass cloth is used with the resin/bondo to attach the satellite
tag. Use caution when working with this material, particularly when
cutting it into smaller strips, because fiberglass fibers or dust
can irritate your skin, eyes, and throat. There are many places
to purchase fiberglass, for example here http://www.shopmaninc.com/cloth.html. Note that usually 4, 5 or 6 oz weights are commonly
used when attaching satellite transmitters. Kevlar/fiberglass cloth
is stronger (and more expensive) than regular fiberglass cloth.
One supplier is available here http://www.shopmaninc.com/hybrids.html
- Other tools and equipment include small wooden tongue depressors
(for mixing resins or epoxy and also for applying resins or epoxy
to carapace and transmitter); latex or rubber gloves; garbage bags
(to collect refuse for proper disposal).
The following workers have glued many transmitters to turtles carapace
and can be contacted for further information:
- G. Balazs, National Marine Fisheries Service, Hawaii, USA <gbalazs@honlab.nmfs.hawaii.edu>
- S. Eckert, Duke University Nicholas School of the Environment
and Earth SciencesMarine Laboratory, USA <seckert@widecast.org>
- B. Godley and A.Broderick, MTRG, University of Exeter in Cornwall,
UK <mtrg@seaturtle.org>
- P. Luschi, University of Pisa, Italy < luschi@discau.unipi.it>
- C. McClellan, Duke University Nicholas School of the Environment
and Earth Sciences Marine Laboratory, USA <catherin@duke.edu>
- K. Pendoley, Perth, Australia <pendoley@newton.dialix.com.au>
- A. Rees, Archelon, Greece <alan@archelon.gr>
If you would like your details added or have any comments then please
contact us at <tagging@seaturtle.org>
- Attachment by tether. Instead of gluing the satellite transmitter
directly to the carapace, the transmitter can be attached to a tether
that is in turn attached to the carapace either by gluing or drilling
a hole. The advantages of this method of attachment are that the transmitter
is more likely to be exposed at the surface when the turtle is breathing
at the surface and hence more likely to transmit information to the
data collection satellites overhead, and they are usually simpler and
faster to attach to the turtle. The disadvantages are that it is likely
that tethered transmitters, as with all attached devices, may increase
the hydrodynamic drag of the turtles, particularly of concern in small
turtles, and also the tether could increase the likelihood of entanglement
in marine debris or underwater structures, particularly when turtles
remain in near-shore waters. The tether is usually designed to break
free if it becomes caught on something, or to break free from the turtle
after a certain amount of time (through degradation of the connecting
joints). For more information, and information regarding the possible
use of Archival Tags in sea turtle research check here (http://www.seaturtle.org/mtn/archives/mtn97/mtn97p3.shtml).
The following workers have attached transmitters to turtles by tether
and should be contacted for further information:
If you would like your details added or have any comments then please
contact us at <tagging@seaturtle.org>
- Attachment by harness. Rather than attach a satellite tag directly
to the carapace of a turtle, you can attach it to a harness that is
then fitted over the turtle, somewhat like a backpack. This has proved
to be a successful technique in leatherback research as it is impossible
to successfully glue a satellite tag to the leathery skin covering the
carapace of leatherbacks. Additional advantages include that it may
be easier and quicker to attach devices to turtles by harness than by
gluing and that short term multiple deployments of the same equipment
can be made. A disadvantage is that the some harnesses are bulky and,
as for all methods to attach satellite transmitters, can possibly affect
the hydrodynamic drag and/or swimming of the turtle during migration.
If possible, you should try to check on the fit of the harness on the
turtle a few days after deployment, and make adjustments as necessary.
The following workers are among those who have attached transmitters
using harnesses and should be contacted for further information:
- S. Eckert, Duke University Nicholas School of the Environment
and Earth Sciences Marine Laboratory, USA <seckert@widecast.org>
- B. Godley, MTRG, University of Exeter in Cornwall, UK <bgodley@seaturtle.org>
- M. Guinea, Charles Darwin University, Australia <michael.guinea@cdu.edu.au>
- G. Hays, University of Wales, Swansea, UK <g.hays@swan.ac.uk>
- P. Luschi, University of Pisa, UK <luschi@discau.unipi.it>
- J. Sperling, University of Queensland, Australia <jsperling@zen.uq.edu.au>
If you would like your details added or have any comments then please
contact us at <tagging@seaturtle.org>
- Attachment by orthopedic screws. As an alternative to harnesses
and tethers, some authors have started to consider the use of technology
derived from orthopedic surgery. See (http://www.seaturtle.org/mtn/archives/mtn95/mtn95p9.shtml)
The following workers have attached transmitters using orthopedic
screws and can be contacted for further information:
If you would like your details added or have any comments then please
contact us at <tagging@seaturtle.org>
The following table overviews the relative benefits and disadvantages
of the different attachment methods. The information in the table
is not exhaustive, and we would appreciate opinions on what additional
factors that other experienced workers think are most salient. Contact
us at <tagging@seaturtle.org>
| Attachment method of satellite tag |
Main benefits |
Main drawbacks |
Other considerations |
| Gluing to carapace (by epoxy and/or fiberglass resin) |
Attachment is usually long term and secure. |
Takes longer to attach transmitter; Epoxy or resin may increase
bio-fouling, which may affect behaviour of turtle; Cannot be used
on leatherbacks. |
Use only epoxies or resins that do not produce much heat during
the curing process, to minimize the chance of thermal injury. |
| Tethering |
Easily attached to the turtle; Only slightly invasive; Can be
used on leatherbacks. |
Can increase drag on smaller turtles; Not usually appropriate
in shallow waters with submerged structures or debris; Deployment
duration may be compromised by the need to minimize chances of
entanglement; Ethical concerns if drilling used. |
Still at experimental stage. |
| Harness |
Easily attached. Can be used on leatherbacks; Has the potential
for multiple redeployment on different individuals. |
Can impede swimming behaviour; Poorly designed or ill-fitting
harness can cause abrasions; May become tangled in debris found
in nearshore waters or on the beach (if attached to a nesting
female). |
Consideration must be given to possibility that harness may
shift or body condition of animal may change. |
| Screws |
Small attachment package; Used on leatherbacks. |
Highly skilled and specialist equipment needed; Ethical concerns
over invasiveness. |
Still at experimental phase. |
Much information can be inferred from satellite tracking data regarding
the behaviour and ecology of marine turtles. Transmitters and satellite
services are constantly being upgraded and thus the field of analysis
and interpretation is highly dynamic. Keep abreast of the literature
as listed in the tagging bibliography and please let us know as new
publications are becoming available: <tagging@seaturtle.org>
If you would like to share your data with the public, or simply take
advantage of the satellite telemetry data management tools available
on seaturtle.org, contact tracking@seaturtle.org.
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