High Early Embryo Mortality and Low Hatching Success Observed in Aldabra Giant Tortoise Populations

Area of Science:

• Conservation Biology
• Reproductive Ecology
• Herpetology

Background:

• Long-lived species often mask reproductive failure through adult census data.
• Aldabra giant tortoises (Aldabrachelys gigantea) are vital for conservation but their reproductive success is poorly understood.
• Assessing early life stages is crucial for accurate population vulnerability predictions.

Purpose of the Study:

• To present preliminary data on fertilization, embryo survival, and hatching success in Aldabra giant tortoises.
• To compare reproductive outcomes across natural and translocated populations.
• To establish baseline productivity metrics for conservation management.

Main Methods:

• Microscopic methods were used to assess egg fertility and embryo viability.
• Fertilization, embryo survival, and hatching success were analyzed across six populations (one natural, five translocated).
• Data were compared with historical estimates and correlated with a Human Modification Index.

Main Results:

• Only 16% of 317 eggs hatched; 97% of failed eggs were undeveloped.
• Complete clutch failure occurred in 67% of clutches.
• Hatching success was significantly lower in translocated populations (0%-26%) compared to the natural population (46%), and below historical rates (60%-80%).

Conclusions:

• Aldabra giant tortoise hatching success is low and variable, primarily due to embryo mortality.
• Translocated populations exhibit markedly reduced reproductive success.
• Incorporating productivity metrics into conservation frameworks is essential for effective management of threatened long-lived species.