Why So Many Turtle Eggs Never Hatch: The Hidden Reproductive Challenges in Testudines

Turtles and tortoises (Order Testudines) are facing serious population declines worldwide, with over 50% of species currently threatened^1,2,3. While habitat loss and climate change are well-known concerns, low hatching success has emerged as another major challenge affecting both wild populations and captive breeding programmes. 

Studies have reported poor hatch rates in several threatened species, including Leatherback turtles, Olive Ridley turtles, and Green turtles. However, recent research suggests that many failed eggs may not actually be “unfertilized” as commonly assumed. 

Fertilization Failure vs Early Embryo Death 

Traditionally, undeveloped eggs are often classified as infertile based on visual examination alone. But researchers now emphasize that hatching failure can occur due to two very different reasons¹: 

• Fertilization failure  

• Early embryonic death  

This distinction is important because both conditions point toward different underlying problems. 

Unfertilized eggs may indicate¹: 

• Poor sperm production  

• Failed copulation  

• Behavioural incompatibility  

Meanwhile, embryo mortality is more commonly associated with¹: 

• Incubation temperature stress  

• Microbial or fungal infections  

• Genetic abnormalities  

• Pollution exposure  

• Poor nest conditions  

As Hemmings, West, & Birkhead (2012) noted, identifying the actual cause of egg failure is essential for improving reproductive success in threatened species⁴. 

Climate Change Is Affecting Reproductive Success 

Temperature plays a critical role in turtle embryo development. Many species require incubation temperatures between 25–34°C for viable development¹. 

Rising global temperatures may therefore increase embryo mortality in some populations. In addition, many turtle species have temperature-dependent sex determination, where warmer nests produce more females. Over time, heavily female-biased populations could reduce fertilization rates and genetic diversity. 

Captive Breeding Programs Face Similar Problems 

Low hatch rates are not limited to wild nests. Captive breeding programmes may also experience: 

• Male infertility  

• Low reproductive hormone levels  

• Copulation issues  

• Nutritional deficiencies  

• Stress after translocation  

The review also highlights the case of the Yangtze giant softshell turtle, where eggs from the last remaining female showed no developmental signs despite conservation efforts and artificial insemination attempts¹. 

New Microscopic Techniques Are Changing Understanding 

One of the most important findings from the review is that many undeveloped eggs previously labelled as infertile were actually fertilized. 

Researchers used microscopic methods to detect: 

• Sperm attached to the perivitelline membrane (PVM)  

• Embryonic nuclei in the germinal disc  

Among successfully examined undeveloped eggs, nearly 75% were confirmed to be fertilized. This suggests that traditional visual assessment methods may significantly overestimate infertility while underestimating early embryo death¹. 

The methods were successfully applied in both captive and wild species, including Hawksbill turtles, Green sea turtles, Galapagos giant tortoises, and Aldabra giant tortoises. 

Why This Matters for Conservation 

The review highlights an important gap in current reproductive investigations. Many studies still fail to differentiate between infertility and embryo mortality, making it difficult to identify the true cause of hatching failure. 

Improved fertility assessment methods may help conservation programmes better understand reproductive barriers, improve hatch success, and support long-term survival of threatened Testudines species. 

Reference 

1. Lavigne A, Bullock R, Shah NJ, Tagg C, Zora A, Hemmings N. Understanding early reproductive failure in turtles and tortoises. Animal Conservation. 2025 Jun;28(3):353-64. https://zslpublications.onlinelibrary.wiley.com/doi/pdfdirect/10.1111/acv.12986 

2. Lovich JE, Ennen JR, Agha M, Gibbons JW. Where have all the turtles gone, and why does it matter?. BioScience. 2018 Oct 1;68(10):771-81. https://academic.oup.com/bioscience/article-pdf/68/10/771/26119354/biy095.pdf 

3. Stanford CB, Iverson JB, Rhodin AG, van Dijk PP, Mittermeier RA, Kuchling G, Berry KH, Bertolero A, Bjorndal KA, Blanck TE, Buhlmann KA. Turtles and tortoises are in trouble. Current biology. 2020 Jun 22;30(12):R721-35. https://www.cell.com/current-biology/pdf/S0960-9822(20)30636-9.pdf 

4. Hemmings N, West M, Birkhead TR. Causes of hatching failure in endangered birds. Biology letters. 2012 Dec 23;8(6):964-7. https://royalsocietypublishing.org/rsbl/article/8/6/964/49316