When is the Right Time to Build a Semi-Natural Nest/Hatchery?
Ideally, sea turtle eggs should be allowed to hatch in their natural nests. Egg relocation activities should only be done as a last resort if protection of the natural nest (in situ) is not possible. In some cases, relocating turtle eggs only yields positive results when the mother turtle lays eggs in dangerous places, for example: the nest is too close to the shoreline, too close to artificial light (lamps), the nest is behind a concrete seawall (which will make it difficult for the hatchlings to reach the sea), the nest is in an eroding area, or the nest is near roads or sidewalks (where the nest and hatchlings could be stepped on). However, in many cases, hatching (in situ) is the best option.
In many places worldwide, egg theft by humans or predation by domestic animals has such serious consequences that it can result in up to 100% egg loss. If humans are the main predators, sea turtle eggs should be relocated, and a semi-natural hatchery should be monitored at all times.
However, it should be noted that the process of relocating sea turtle eggs to a semi-natural hatchery often poses greater risks than those arising from predation by natural predators. Therefore, conservationists should seriously weigh the pros and cons of the egg relocation program compared to letting the turtle nests hatch naturally.
In some areas, predation by domestic animals (which are not natural predators of turtle eggs/hatchlings) can be very serious, thus allowing for semi-natural hatchery programs. These animals include dogs, cats, and pigs. Additionally, some animal species may experience population booms due to human presence. This situation can occur when humans compete with natural predators of turtle eggs (such as civets, rats, and eagles) for food, or even eliminate the natural enemies of these predators. In such cases, eradicating natural predators can be considered an alternative to using hatcheries.
Disadvantages of Semi-Natural Hatcheries
Because semi-natural hatchery programs have several weaknesses, a thorough evaluation must be carried out, setting aside manipulative, impractical, or ineffective options. Before implementing a hatchery program, several factors should be considered, as follows:
- Semi-natural hatchery programs are very costly and require many human resources to collect and care for each relocated egg.
- The effectiveness of this program depends heavily on skilled personnel and reliable staff. However, the available budget often only allows for minimal wages or full reliance on volunteers.
- The success rate of hatching in a semi-natural hatchery is usually very low compared to hatching in natural nests, even with the involvement of professionals.
- The sex ratio (gender ratio) is often imbalanced, depending on the conditions in the semi-natural hatchery.
- Unnecessary release methods increase the risk of hatchling death. When hatchlings are regularly released in the same spot, it encourages fish to form a “feeding station,” causing predator fish to memorize the release points. Moreover, hatchlings released (usually in the morning) are often exhausted from their futile attempts to find their way to the sea. Hatchlings typically hatch a few hours after sunset and may wander aimlessly around the hatchery throughout the night. There’s a significant risk that hatchlings will be eaten by ants, crabs, birds, rats, cats, dogs, or small mammals.
- A semi-natural hatchery program designed to reduce hatchling mortality may cause over-dependence on human intervention, which is unrealistic to sustain continuously and long-term.
- The semi-natural hatchery program also has significant negative impacts on human psychology. It requires a large human workforce, and program managers often promote their efforts as doing more for turtles than they actually have. As a result, more effective natural programs, which are politically less appealing, may be overlooked.
Recommended Semi-Natural Hatchery Methodology
Construction and Placement of the Semi-Natural Hatchery
A semi-natural hatchery should be built as close to the beach as possible to minimize physical trauma during the egg transportation process and to shorten the time between when the turtle lays the eggs and when they are placed in the semi-natural hatchery. Placing the hatchery near the beach also provides the opportunity for embryos and hatchlings to undergo imprinting (learning the surrounding environmental conditions). To maximize the diversity of environmental conditions where the eggs are planted, multiple hatcheries should be built if possible—the more, the better. The semi-natural hatchery should be built to closely resemble a natural nest. It is important to remember that the temperature in the semi-natural hatchery should replicate the temperature of a natural nest.
All turtle species lay eggs above the high-water mark on the beach. The surface of the semi-natural hatchery should be at least 1 meter above the highest tide line to avoid flooding by rising tides, which would cause the eggs to rot. Avoid placing the semi-natural hatchery in areas affected by waves or too close to unpredictable river mouths, as this could damage the hatchery. The hatchery should be fenced and covered with mesh wire. To protect the eggs from crabs or other tunneling animals, the mesh wire should be buried at least 0.5 meters deep in the soil. Additionally, to prevent fungi or bacteria, the sand in the semi-natural hatchery should not be used to hatch turtle eggs for more than one egg-laying season.
In beaches experiencing erosion at certain points or human disturbance (not exploitative), nests under threat may be selectively relocated to safer areas on the same beach. If predators and humans are not serious threats, it is better not to build a semi-natural hatchery but instead protect the nest with a cylinder net. This way, the hatchlings do not become dependent on human intervention to reach the sea.
How Many Eggs Need to Be Relocated?
Many conservationists believe that to maintain a healthy nesting population, at least 70% of eggs/nests should be protected or secured. However, in some over-exploited areas, 100% protection is needed. In places with consistent weather patterns, hatchlings may hatch as males one season and as females the next. To ensure a balanced sex ratio, hatchery programs should be run continuously throughout the season in sufficient numbers.
Egg Collection and Transportation
To reduce embryo mortality, all eggs should be planted/buried within 2 hours (no egg should be left exposed for more than 5 hours). Technically, workers are allowed to catch the eggs with both hands right after the turtle lays them, then gently place them in a bucket filled with sand. Another method is to place a large plastic bag under the turtle’s cloaca. It’s important not to disturb the nest or the turtle, and ensure that the eggs fall directly into the plastic bag without sand sticking to them (this is preferable). Workers must be quick to remove the eggs from the bag before the mother buries them. The bag is then placed in a bucket. However, in other situations, the eggs can only be collected after the mother turtle returns to the sea. All eggs should be handled very gently, and if transported by vehicle, care should be taken to cushion the eggs to prevent them from colliding with each other.
Handling Older Eggs
Eggs older than two hours require special attention (for example, eggs found in the morning or those that are halfway through incubation but are threatened by erosion). The soft membranes of older eggs can easily rupture if flipped or rotated. Mark the top side of the egg with a pen to ensure it is placed correctly. For transportation, non-elastic containers such as buckets should be used (do not use plastic bags) to prevent eggs from being squeezed or flipped.
Planting Turtle Eggs
The conditions in the semi-natural hatchery should closely resemble the natural nest environment. Each semi-natural nest should be spaced at least one meter apart to prevent interference with other nests and provide enough space for workers to safely move around the hatchery. The nests should be shaped like a bottle or jar, rounded at the bottom and straight up to the surface. The depth of the semi-natural nest should mimic that of a natural nest.
If digging the semi-natural nest encounters obstacles, such as collapsing walls (especially during the dry season), water can be sprayed on the sand before continuing to dig. Eggs should be placed in the nest gently, and they should be no older than two hours. The moist sand should be used to cover the eggs with a thickness of 8-12 cm. Dry sand should not touch the eggs directly and should only be used to cover the top layer of the nest. Each nest should be marked according to the recording data.
Cylinder Nets
Some conservation managers suggest placing a cylinder net over each nest. The net should be made of nylon with holes smaller than 1 cm. Chicken wire should not be used because the hole size is too large and could injure the hatchlings as they pass through. The nylon net should be cut to a height of 40 cm and a width of 195 cm to form a 60 cm diameter cylinder. A 0.25 cm metal rod is used to secure the ends of the nylon cylinder and to anchor it into the ground. The net should be buried at least 10 cm deep to protect the nest from underground animals such as crabs. A mosquito net or another nylon cover can be placed over the cylinder to protect it from predators, depending on the level of predator threat.
This method has the advantage of allowing hatchlings to be counted, recorded, and data to be collected precisely. However, the downside is that hatchlings may become exhausted and less agile, or even face death from predators.
Releasing Hatchlings
In natural conditions, hatchlings would enter the water at random points at unpredictable times. Ideally, hatchlings from semi-natural nests should be released into the sea immediately after they emerge from the sand. However, it’s better to wait briefly for other hatchlings to emerge from the sand to form a larger group. To create random release points (to avoid predators from memorizing release locations), each release point should be several hundred meters apart.
Special Techniques
Special hatching techniques have been used with varying success in different locations. In the Philippines, Sabah’s turtle island, Pacific beaches in Guatemala, and other places, “hot” semi-natural nests have been suspected of producing all-female hatchlings. Therefore, some semi-natural nests have been shaded with coconut leaves. In Malaysia, dividing a nest into two parts with a 60:40 ratio, each planted in separate semi-natural nests, has resulted in successful hatching.
In Natal Beach, South Africa, successful hatching was carried out in a nylon cylinder net, then planted in a semi-natural nest inside a basket. However, when the same technique was applied in Malaysia, it led to 100% egg mortality during embryo and hatchling stages.
Literature Cited
Chan, E.-H. and H.-C. Liew. 1996. Decline of the leatherback population in Terengganu, Malaysia, 1956-1995. Celonian Conservation and Biology2:196-203.
Godfrey, M. H. and N. Mrosovsky. 1994. Simple method of estimating mean incubation temperatures on sea turtle beaches. Copeia 1994:808-811.
Harry, J. L. and C. J. Limpus. 1989. Low-temperature protection of marine turtle eggs during long-distance relocation. Australian Wildlife Research 16:317-320. Mortimer, J. A., A. Zaid, K. Safee, M. Dzuhari, D. Sharma and S. Aikanathan. 1994. Evaluation of the practice of splitting sea turtle egg clutches under hatch- ery conditions in Malaysia, p.118-120. In: B. A.
Schroeder and B. E. Witherington (Compilers), Proceedings of the Thirteenth Annual Symposium on Sea Turtle Biology and Conservation. NOAA Technical Memorandum NMF
Research and Management Techniques for the Conservation of Sea Turtles Prepared by IUCN/SSC Marine Turtle Specialist Group
Edited by Karen L. Eckert
Karen A. Bjorndal
- Alberto Abreu-Grobois
- Donnelly
