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Background of the Study
Six of the seven species of sea turtles are listed as Endangered or Critically Endangered. In the Pacific region, leatherbacks turtles are heading for extinction and in the Mediterranean, green turtle numbers have plummeted. Sea turtles appear to have the potential to reproduce abundantly by females can lay hundreds of eggs in one nesting season. But even under natural conditions, relatively few young turtles will survive during their first year of life.
The sea turtle hatchling phase is believed to be the life stage at highest rate of mortality, as scientists estimate that only a few per thousand hatchlings manage to survive to reach sexual maturity (Limpus, 1985). In some extreme cases, the figure may be only a few per ten thousand (Frazer, 1986). Thus, research on sea turtle hatchlings, particularly investigating factors that may influence their chances of survival is crucial for sea turtle conservation.
Sea turtle hatchlings are particularly vulnerable to predation, both during the crawl (from the nest to the sea) and in the initial phase of their swim away from the beach when they cross shallow, predator rich near-shore waters (Salmon and Wyneken, 1987; Pilcher et al., 2000; Gyuris, 2000). The initial swimming phase lasts for approximately 24 hours (Wyneken and Salmon, 1992) and it is characterized by almost continuous 'frenzied' swimming, which facilitates the rapid movement of hatchlings away from shallow near-shore areas (Wyneken, 2000). Factors which confound or delay the completion of this phase may significantly increase hatchling mortality (Whelan and Wyneken, 2007).
Hatchlings that do succeed in reaching the sea after suffering a prolonged period in the nest or prolonged periods on the beach due to disorientation have been shown to compromise the frenzied swim offshore. Lorne and Salmon (2007) reported hatchlings that have completed seaward crawls were able to orient away from shore in the absences of wave cues; whereas those placed in the sea after two hours of disorientation were unable to do so. Furthermore, hatchling activities and swim speed are known to decrease with increased retention time after emergence (Pilcher and Enderby, 2001).
During the first year, many species of sea turtles are rarely seen. This first year is termed as the "lost year" to emphasize this gap in sea turtle life history information. From this moment on, observation becomes extremely difficult to the researchers. Carr (1952) claimed that the location of hatchling and post-hatchling turtles go and what they do during their 'lost' years as critical for the restoration of green turtle populations. Carr (1952) also pointed out the hopelessness of conservation and restoration of sea turtles until the basic biology of the species is better known.
Taking all these circumstances into account, it is very importance to make every hatchling entering the water column. These hatchlings have to be as healthy as possible and had higher chances to survive the long swim ahead. If hatchlings are compromised during this crucial stage they will have a decreased chance of reaching adulthood.
Throughout the world, green turtle (Chelonia mydas) population have experienced significant declines over the past 100 years, especially due to habitat degradation (alteration or destruction) among other reasons as reviewed by Lutcavage et al. (1997). Hence, the green turtle is currently recognised internationally as species of conservation concern and in 2002 was placed in the IUCN (World Conservation Union) Red List of Threatened Animals. Thus, there is active management of sea turtle rookeries in many regions of the world, including movement of whole clutches of eggs into hatcheries. However, the relocation of clutches should be undertaken only if by leaving the clutches in-situ (undisturbed), will resulting their destruction (Mortimer, 1999).
1.2 Justification of the Study
There are two methods used to incubate eggs clutches of sea turtle in Malaysia which are the in-situ and ex-situ practices. The first method, known as in-situ method, is a practice where the nest is marked and left undisturbed to incubate naturally after laid by females. Once hatched the hatchlings from in-situ nests crawl downhill towards the water line.
The second method was the relocation of egg clutch immediately after egg laying known as the ex-situ method. This method is usually applied to protect clutches from inundation of sea water if the nest is located too close to the high tide mark, or from predation by humans or other animals. Relocated eggs will be buried in a protected beach hatchery or in a styrofoam boxes. Upon emergence, hatchlings will be collected and released at a certain point on the nesting beach.
Majority of the sea turtle conservation in Malaysia are practising ex-situ egg incubation method. Sea turtle nests are transferred in a protected beach hatchery. In some cases, the nests will be incubated in styrofoam boxes. Even though ex-situ is not recommended in sea turtle conservation, in certain cases this method is used when some circumstances occurred that do not allow the use of the hatchery. For example, Cherating Turtle Sanctuary in early 2009, the hatchery was still under renovation, resulting in the use of styrofoam boxes. In the Geliga and Kemaman sanctuaries, they had to incubate eggs in styrofoam boxes because insufficient funds were available to manage the hatchery.
In the meantime, only Redang Island sanctuaries keep practising in-situ incubation method. Three nesting beaches in Redang Island are Mak Kepit and Mak Simpan managed by Department of Fisheries Terengganu and Chagar Hutang managed by the Sea Turtle Research Unit (SEATRU) of Universiti Malaysia Terengganu (UMT). Most of the time they are practising in-situ method but during north-east monsoon season (October and December) they switch to the styrofoam box incubation method.
Although different methods are used to incubate clutches of eggs in sanctuary management, the quality of hatchlings (in terms of locomotors performance and morphological characteristic) produced by these different methods is unknown, and needs to be investigated. More than half a million green turtle hatchlings have been released to the sea annually from whole sea turtle sanctuaries in Peninsular Malaysia (east and west coast) over the last decade as recorded by Department of Fisheries in 2009. However, we are worried if these sanctuaries are producing poor quality of hatchlings and resulting to the relatively small contributions of sea turtle population in the future.
In order to test whether incubation method influences the quality of hatchlings, hatchling crawling and initial swimming performance were measured as an index of hatchling quality. Both these performance measures are likely to affect the predation rate of hatchlings as they proceed down the beach and swim off into the relative safety of deeper off-shore waters. As mentioned previously, hatchlings have to be as healthy as possible and this will give the best chance for them to survive during swimming across the predator rich near-shore waters.
Previous studies in Malaysia only address the hatched success of sea turtle hatchlings by comparing the usage of different incubation methods. Hence, the question appears here whether our hatchlings in reality survive during early swimming or we are bringing them into high risk of predation. Results from this study will lead to the reassessment of the usage of these three incubation methods from different perspective which is in term of hatchlings morphological characteristic and their locomotors performance. It is hope that, this study will provide information to improve our conservation efforts towards more quality hatchlings production.
The major aims of this study were:
To assess the temperature profiling of in-situ and ex-situ eggs incubation methods;
To compare swimming performance and crawling speed of green turtle hatchlings incubated in the in-situ and ex-situ;
To determine the relationship between eggs incubation temperature and morphological characteristics of hatchlings with the hatchlings' locomotors performance.