Mirza Pedju and Rod Salm discuss the distinguishing features of turtle tracks. Photo: Rizya Ardiwijaya
By Dr. Rod Salm
An expedition that combined natural history exploration, visiting a new area and even some “crime scene investigation” in turtle nesting areas? I didn’t need to be asked twice!
I first came to Sumba – an island in eastern Indonesian — in 1973. Now I was back, on a part of the island I had never visited to assess the conservation values of the area.
Among several other conservation priorities, we were especially interested in the turtle nesting beaches.
We were invited by the founder of the local Nihiwatu Resort, Claude Graves, a committed investor in local community programs, to help him think through the establishment of conservation practices over the coastal and marine habitats adjacent to his resort and in the potential marine protected area lying just a mile or so southeast of his resort.
This site was identified through a Nature Conservancy study as an area of interest for conservation, though its full potential was yet to be verified.
I hardly needed my arm twisted to accompany Mirza Pedju and Rizya Ardiwijaya to explore a new area and do some real exploratory natural history. I was keen to undertake assessments of potential nesting beaches to try to ascertain:
- Did turtles nest on these beaches?
- If so, which species and in what numbers?
- Were the eggs harvested by people or predators? And
- What chances did the beaches have of surviving sea level rise?
Mirza Pedju walking alongside tracks of loggerhead turtle (alternating hind flipper impressions with wavy center track and no tail drag mark) that crosses the high tide mark and enters and exits bushes where the turtle laid its eggs. Photo: Rod Salm
This requires some forensics to determine whether the depressions high up the beach are made by turtles, dogs, pigs, or monitor lizards to determine whether in fact turtles do nest there and in what kinds of numbers, and some CSI to determine what disturbed the nests and unearthed the eggs. Here is our story.
On the Trail of Sea Turtles
First we cruised close to the beach by boat – I saw two turtle tracks on one and pointed these out. We eagerly plunged into the sea, and surfed ashore.
Once on shore, we identified the likely turtle species by its crawl track: this is relatively easy as the tracks are quite distinctive in both width and pattern.
The first track was that of a green turtle (Chelonia mydas) and easily identified. The green turtle moves up the beach in a breaststroke motion, pulling back on its fore flippers together and pushing forward with its hind flippers together.
The result is a straight track with closely spaced parallel depressions made by the hind flippers, impressions of the fore flippers that extend beyond the margin of the track, and a central straight drag mark of the tail down the center of the track.
Distinctive track of a green turtle (Chelonia mydas) moving up the beach that shows parallel depressions made by the hind flippers, straight central track with a clearly defined tail drag mark down the middle. Photo: Rizya Ardiwijaya
We followed the track up the beach and found that the turtle had crawled up above the high tide line and then turned around returning to the sea. That the track crossed the tideline indicated that it was indeed one from the previous night.
Track of a green turtle emerging, doing a U-turn and then returning to the sea without nesting. Photo: Rizya Ardiwijaya
From there we walked to the closer end of the beach and back searching the upper end of the beach and under the vegetation for old signs of nesting (large pits) and keeping our eyes open for pig, dog, monitor lizard, and people tracks. We found all but dog tracks; and the people tracks were very fresh and likely from this morning. Were people foraging for turtle eggs on this beach? We were soon to find out.
At the top of the beach and partly under the cover of the palm-like screw pine, Pandanus, we found the first pit. It was old and difficult to tell whether dug by a turtle or other natural beach scavengers.
I filtered through the upper layers of sand and some found pieces of old turtle shell. The prognosis was good as these were yellowed and not punctured by the kinds of holes made by crabs and other predators.
We marked this as a successful turtle nest from which the hatchlings had emerged. Good news.
We found another nest pit nearby, but this one had a littering of fresh white colored egg shells perforated by holes. Bad news: the nest had been dug up by predators and the eggs eaten.
We could have dug into the nest to determine whether any eggs survived, but didn’t want to disturb the nest further in case there were viable eggs still planted in the sand. In such cases, I fill in the nest cavity with sand to prevent crabs and monitor lizards from digging out the remaining eggs.
Turtle nest pit excavated by predators. The white egg cases with puncture marks are scattered across the sand.
While searching around in the brush we found two huge mounds made by the megapode or orange-footed scrubfowl, Megapodius reinwardt. As its name suggests, this is a large footed bird: the males and females work together to scrape leaf litter into a huge mound in which the eggs are laid.
The warmth produced by the decomposing leaves incubates the eggs and frees the megapodes to get on with their lives but for regular visits to maintain the mound and scrape or add vegetation to regulate the incubation temperature. This discovery was an added bonus, enhancing the conservation value of the beaches.
What About Sea Level Rise?
The ultimate test remained: would the beaches fare well in the face of sea level rise? It was clear that some beaches would not likely persist as sea levels rose because they were backed by low cliffs or steep rocky slopes. The sand would have nowhere to go but out to sea as waves bounced back from the high rocky ground behind the beaches and carved them away.
Some beaches on the other hand were backed by low-lying sandy plains or a low dune separating them from low ground. These kinds of beaches have great prospects for persisting as sea-level rises because the sand will get pushed inland, even as the beach retreats.
Assessing the prospects for turtle beach persistence through sea level rise is an important consideration in deciding our conservation priorities and managing activities that might impede this process.
We already knew turtles nested on the more accessible beaches as the resort buys eggs collected for local markets and raises them in a hatchery, releasing the hatchlings on their beach to head out to sea.
Our quick snapshot of the beaches confirmed that turtles nest in the proposed marine protected area southeast of the resort. To confirm exactly which species nest when and in what numbers would need more work.
We learnt too that some egg clutches are lost to predators and people but others hatch, and there are beaches that have good prospects of persisting through sea level rise. The prognosis is good for turtles there if the beaches are protected and predation carefully managed.
As a sequel to this story, our Savu Sea team were encouraged by our rapid assessment findings and, at their request, I have just completed a rapid turtle beach assessment protocol for them to take these assessments to other beaches around Sumba and its neighboring islands.
Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.