ea turtles not only have hard shells, they also have hard-to-understand, complex lives. They guard age-old secrets, even from dedicated scientists.

Every few years, each adult female green turtle migrates to a remote nesting beach to breed and lay eggs. When her first clutch of about 100 eggs is developed, she climbs up the beach and digs a nest for depositing her eggs, a process that takes about an hour or two. After she has successfully laid the eggs, she goes back to the sea. She lays eggs at two-week intervals three to five times in a nesting season, over a period of several months. After the last clutch is laid, she disappears back into the ocean, not to be seen again for several years. Only the nesting females come out on beaches, so the lives of the males and young turtles are even more mysterious.

The Turtle Islands Heritage Protected Area (TIHPA) is a wonderful place to learn about sea turtles, at least during those few hours of their life when they are on the nesting beach. Malaysia's Sabah Parks and the Philippines' Department of Environment and Natural Resources (DENR) have managed to protect much of this magnificent turtle rookery, which is unique in Southeast Asia. Sea turtles are completely protected within the TIHPA, although egg collection is allowed in five of the Philippine Turtle Islands.

But what happens once the turtles leave the safe shores? What hazards have man and nature put in their way out in the vast ocean? Where do the turtles travel? Where would we find them again? What threats do they encounter as they migrate to and from their sanctuary in the Turtle Islands? What can we do to make their lives as safe as possible during their migration, and wherever they end up?

DENR ranger puts flipper tags on the foreflippers of a green turtle after the turtle finished nesting on Baguan Island (Stuewe, Oct. 1998)

The Pawikan Conservation Project (PCP) tagged 8,071 turtles with flipper tags on the Philippine Turtle Islands from 1984 to 1998. De Silva (1996) and De Veyra (1994) reported that many turtles tagged on the Malaysian Turtle Islands were recovered in Philippine waters and most of these were actually recaptured on the neighboring Philippine Turtle Islands. Similarly, most of PCP's reported returns come from the Malaysian Turtle Islands, while only a couple of turtles with tags were recovered in other parts of the Philippines.

But could it be that large numbers of tags are recovered in some places because people in those places are more helpful at reporting the information? Just because there are no tag returns from some places is no proof that the turtles are not migrating there -- it only means that there are no reports from those places!

Recapture locations of green turtles tagged after completion of nesting in the Philippine-Sabah Turtle Islands between 1972 to 1994 (Sabah Parks: Development and Management Plan for Turtle Islands park, 1996; De Silva, 1996). (Click image to enlarge)

From the tag returns we know that Turtle Islands turtles can go to very distant places.

But how do they travel to these distant places? Do all turtles take the same route? Do they go more often to some places than others? Are those places safe?

How can we solve these puzzles? 

This is where satellite tracking comes in. The US National Oceanographic and Atmospheric Administration's Tiros satellite originally designed for gathering meteorological information has a special instrument on board that oceanographers and wildlife biologists around the world use to track buoys and animals. The animals are fitted out with transmitters that relay their location and some other data to the scientists via the satellites.

In October 1998, we put satellite transmitters on two green turtles nesting on the Turtle Islands.

You usually have only one shot at marking a turtle with satellite transmitter. Once she disappears in the ocean, you may never get your hands on the transmitter again.

Before we attached the transmitters to the turtles, therefore, we wanted to make sure the transmitters were working. We let them transmit signals from a table on the beach to check whether they could correctly locate the PCP field station on Baguan Island. They worked as expected.

Jack Frazier puts the last coat of green, anti-fouling paint on one of our satellite transmitters, while it is being tested on the beach at Baguan Island (Stuewe, Oct. 1998)

Location of the transmitter test site in front of the PCP field station on Baguan Island (IPAS, 1991)

Once everything was ready, the DENR's tagging team spent the following nights carefully observing Baguan's beaches to find a nesting turtle that had been recorded on the beach earlier that year. We really wanted a female that had already nested on this beach several times this season and was ready to start her migration. We reasoned that a turtle that would hang around the islands for a long time to wait for more clutches of eggs to mature would be likely to spend weeks resting under the sharp corals around the islands. That meant there was a pretty good chance that the corals would break the antenna. Even worse, perhaps she would be caught by one of the trawlers or on a long-line and never be able to start her migration.

We compared the turtles' flipper tags with PCP's database of this year's nestings. When our taggers finally found the right turtle, we stopped her just before she finished nesting. Quickly the marking team assembled. We put some tough Epoxy glue on the bottom of the transmitter, then immediately cleaned the turtle's carapace of any sand and other obstructions.

Jack Frazier (left) squirts Epoxy on the bottom of the transmitter as Rhoda de Veyra (middle) and Bian Mejino (right) carefully hold the transmitter upside down (Stuewe, Oct. 1998)

Then Jack put the transmitter onto the highest part on the turtle's carapace (top shell), pushing hard so it really stuck to the carapace.

Jack pushes the satellite transmitter firmly onto the turtle's shell (Stuewe, Oct. 1998)

We gave the epoxy a few minutes to dry and then it was just a matter of waiting until the turtle returned to the sea. The whole operation took less than 20 minutes.

Hani on the beach after being tagged. (Dumaup, October 1998)

Once the transmitters were attached, we faced an even more difficult task: how to name each turtle. This is what we ended up with:

YUMI
(pronounced like the English words "you-me")
This turtle was so quiet that we decided to call her Yumi, short for the Tagalog word Mayumi, which means demure or modest.

HANI
(pronounced like the English word "honey")
We were so fascinated by this turtle that Dr. Rhoda de Veyra, head of the DENR tagging team, decided to name her Hani, the nickname for the Tagalog Mabighani, meaning attractive or alluring.

The first transmitter was attached to Yumi on October 16, 1998 and the second to Hani the following night. We received good signals with good position information from at least one transmitter until January 29, 1999, after which the quality of the signals deteriorated (the last transmission from these first two transmitters was received on February 27, 1999). Not all signals gave accurate locations. Sometimes, the turtle was simply not on the surface long enough for the transmitter to send a clear signal to the satellite. But there were enough good locations to get a good idea of what the turtles did after returning to the sea. We put these positions on a map to show where the turtles were located by satellite after they went back into the sea.

The tracking data contain a lot of information. To get to all that information, we listed the data in different formats. We plotted the turtles' routes on maps of the Sulu Sea; we animated their movements so one can play with them in an interactive video; and we tabulated the raw satellite data so one can get an idea about the accuracy of the individual locations.

Migration path of Yumi

Migration path of Hani

We have been able to learn several interesting things from the satellite tracking of these first two pilot turtles .

Turtle Islands Protected Area Boundary
Our turtles, rather unexpectedly, stayed near the Turtle Islands for several weeks. This generated a first very intersting set of data for us: the average distance these turtles spent away from the shoreline while they were waiting for their next clutch of eggs to mature.

Map with the ideal protection range. The circle encloses the area around Baguan Island that Yumi and Hani may have used when they were waiting for yet another clutch of eggs to mature (WWF-Philippines, 1999) (click map to enlarge)

As turtles may climb up the beach up to seven times in a single nesting season to lay new clutches of eggs, they can spend a significant amount of time near the nesting beaches. These waters need to be as safe as possible so the turtles are not scooped up by trawls or caught on long-line hooks. The marine border of the protected area within which no hazardous fishing is allowed should reach far enough to include the areas where turtles rest between their successive nestings. We now have an idea how far that border should be: about 40 km based on what the satellite transmitters of our first two turtles "told" us.

Migratory Routes
The second class of information we collected was the migration routes the turtles took after leaving the nesting area.

Hani set off from the waters of Turtle Islands on 22 November, more than a month after she was tagged while nesting on Baguan. During this period she was recorded back on Baguan at least once, nesting again on November 6, 1998.

Yumi finally left on 1 January 1999, covering about 130 km in 18 hours on a fairly straight, southeasterly heading. On January 3 between 1 p.m. and 10 p.m. Greenwich Mean Time (GMT), she changed course, making a 90-degree turn north and then continuing for about 23 km over the next 8 hours. She seems to have followed a track that brought her close to whatever islands there were in this direction. From 6 January 1999 she remained in the general vicinity of Jolo and Basilan Islands in Southwestern Mindanao at about 6.5^o N and 120.5^o E.

Why did both turtles set out on the same track? Why Yumi then make this sudden turn? What did she notice? What made her stay near Jolo and Basilan? What was so exciting there? Did our turtles continue their migration after we stopped getting their satellite signals?

We don't know the answers to these questions yet. There are no cameras on our transmitters. But we are trying to find out. Of course we have been thinking about an explanation. One likely reason: seagrass beds, the favorite food of our green turtles. Maybe after all that egg laying and fasting, Yumi had a big feast before continuing with her further travels? On the other hand, maybe she will stay in the vicinity of Jolo and Basilan until she returns to Turtle Islands in a few years? More unanswered questions.

Unfortunately, the signals from our turtles started to come in less often and with poor quality position information towards the end of January 1999. Probably, the antennas had been damaged by rocks and corals under which the turtles were resting. For several months now, both Yumi and Hani have been "off the air" and we can only hope to find them again when they next come to the Baguan nesting beach.

Related story: How to track turtles by satellite.