Relocate nests/eggs for artificial incubation: Sea turtles
Overall effectiveness category Awaiting assessment
Number of studies: 15
Background information and definitions
Relocating eggs to artificially incubate them may be used as a way to maximise hatching success as the eggs will no longer be vulnerable to natural threats such as predation. Consideration must be given to the potential impacts of incubation conditions (for example temperature and humidity) on the sex, size, shape, colour, behaviour, movement ability and post-hatching growth of reptile hatchlings (Warner & Andrews 2002, Booth et al. 2006).
This action includes studies where eggs are incubated in artificial conditions, which ranges from controlled laboratory settings to using polystyrene boxes to incubate eggs in buildings. Studies are also included where gravid females are brought into captivity to lay eggs, but eggs are taken away from the females for artificial incubation.
Due to the number of studies found, this action has been split by species group, though no studies were found for amphisbaenians. See here for: Tortoises, terrapins, side-necked & softshell turtles; Snakes & lizards; Crocodilians or Tuatara.
For studies that discuss the effects of relocating and re-burying eggs in natural habitats to avoid threats, see Relocate nests/eggs to a hatchery and Relocate nests/eggs to nearby natural setting (not including hatcheries).
Booth D.T. (2006) Influence of incubation temperature on hatchling phenotype in reptiles. Physiological and Biochemical Zoology, 79, 274–281.
Warner D.A. & Andrews R.M. (2002) Laboratory and field experiments identify sources of variation in phenotypes and survival of hatchling lizards. Biological Journal of the Linnean Society, 76, 105–124.
Supporting evidence from individual studies
A replicated study in 1971–1973 of turtle eggs collected from Surinam, Ascension Island and Costa Rica (Simon 1975) found that at least half of green turtle Chelonia mydas eggs that were relocated and artificially incubated hatched successfully over three years. In the first year, 14,346 of 30,000 (48%) green turtle eggs hatched successfully. In the second year, 34,527 of 61,257 (56%) green turtle eggs hatched successfully. In the third year, 76,024 of 97,312 (78%) green turtle eggs hatched successfully. In 1971–1973, seven batches of green turtle eggs (14,803–63,404 eggs/batch, 1–3 batches/year) were collected from Surinam (3 batches), Ascension Island (2 batches) and Costa Rica (2 batches), placed in Styrofoam incubation boxes with sand (approximately 88 eggs/box) and relocated to open-sided wooden shelters at a turtle farm on Grand Cayman. The top layer of sand inside the boxes was periodically moistened with water and was removed 3–5 days before hatching was expected. Numbers of infertile eggs, unviable and viable hatchlings were recorded after hatchlings had emerged.Study and other actions tested
A replicated, controlled study on a sandy beach in Suriname (Mrosovsky 1982) found that artificially incubated green turtle Chelonia mydas eggs produced a lower percentage of female hatchlings compared to natural nests. The percentage of female hatchlings was lower in nest boxes (41 of 97, 42% [numbers from table]) compared to natural nests (77 of 120, 64%). Temperatures in incubation boxes may have been cooler than those in the sand of the nesting beach (box: 27.4°C; beach: 28.8°C), and average incubation periods were longer (box: 63 days; beach: 57 days), although these results were not tested statistically. Ten clutches of eggs were incubated in polystyrene boxes with around 88 eggs/box, and a further 12 clutches were left in the sand where they were laid. Temperature was measured in an additional incubation box, though the hatchlings from this box were not included in the analysis. Temperatures on the beach were taken at a depth of 80 cm, in an unshaded area where turtles nest. Temperature readings were taken at 3 h intervals in early June. Ten hatchlings from each clutch were euthanized and their gonads were dissected to determine the sex.Study and other actions tested
A study in 1979 at a sea turtle farm in the Cayman Islands (Critchley et al. 1983) found that 26–58% of green turtle Chelonia mydas eggs collected from a captive colony hatched when artificially incubated in sand-packed and foam-layered Styrofoam boxes. Results were not statistically tested. In a small-scale trial, hatching success of eggs incubated in foam-packed boxes was 58% (undeveloped eggs: 15%, developing eggs that didn’t hatch: 27%) and hatching success of eggs incubated in sand-packed boxes was 48% (undeveloped eggs: 20%, developing eggs that didn’t hatch: 31%; egg numbers not provided). In a larger trial, hatching success of eggs incubated in foam-packed boxes was 30% (1,311 of 4,400 eggs) compared to 26% hatching success of eggs incubated in sand-packed boxes (11,004 of 42,000 eggs). In an initial trial to compare incubation approaches, nine green turtle clutches were divided, and half of the eggs were placed in Styrofoam boxes packed in sand and the other half were placed in Styrofoam boxes packed in between layers of perforated polyethylene foam (3.8 cm thick). Each box contained 56–97 eggs. Following this trial 4,400 eggs collected in 1979 were incubated in foam-packed boxes and hatching success compared to 42,000 eggs incubated in sand-packed boxes.Study and other actions tested
A replicated, randomized, controlled study in 1980 and 1982 on a sandy beach in Suriname (Dutton et al. 1985) found that artificially incubating leatherback turtle Dermochelys coriacea nests in Styrofoam boxes produced all male hatchlings whereas natural nests produced mixed sex ratios and reburied nests produced all female hatchlings. Leatherback turtle eggs incubated in Styrofoam boxes produced no female hatchlings, compared to 30–100% of female hatchlings in natural nests and 100% female hatchlings in reburied nests. Incubation duration was 70–73 days in Styrofoam boxes and 60–66 days in natural nests (results not statistically tested). Leatherback turtle eggs from five clutches laid in 1980 and 10 clutches laid in 1982 were incubated in Styrofoam boxes (45–60 eggs/box). In 1980, ten embryos were sampled and sexed prior to hatching. In 1982, ten hatchlings were randomly selected from each box after emergence, euthanised and sexed. Sex ratios were compared to 10 hatchlings/clutch of two naturally-incubated nests laid in 1980, six naturally-incubated nests laid in 1982 and two clutches laid in 1982 below the tide line that were reburied elsewhere on the beach.Study and other actions tested
A replicated, controlled study in 1982 on a sandy beach in Suriname (Whitmore & Dutton 1985) found that leatherback Dermochelys coriacea and green Chelonia mydas turtle nests incubated in Styrofoam boxes had comparable hatching success to natural nests not washed over by sea swells, but greater incidences of embryonic mortality and deformity than natural nests. Average hatching success of turtle clutches relocated to Styrofoam boxes was 60–73% compared to 33–67% in natural nests washed by sea swells, and 62–82% in natural nests not washed by sea swells (results were not statistically tested). Embryonic mortality and deformity occurred more often in eggs incubated in Styrofoam boxes (mortality: 26–33% of eggs, deformity occurred in 50–88% of clutches) than natural nests (mortality: 8–21% of eggs, deformity: 10–20% of clutches). No eggs incubated in Styrofoam boxes were predated whereas in natural nests 17–27% of leatherback and 11–12% of green turtle eggs were predated. Some leatherback turtle nests were reburied further up the nesting beach for comparison (see original paper, or “Relocate eggs/nests away from threats”). Nesting turtles were surveyed at least once/week in March – August 1982 on a 12 km long beach. Nests laid below the spring high tide line were relocated the next day to a hatchery for incubation above ground in Styrofoam boxes (11 leatherback clutches, 45 eggs/box; 8 green turtle clutches, 88 eggs/box). Relocated and natural nests (~35 green turtle and ~30 leatherback nests) were excavated after emergence to evaluate hatching success.Study and other actions tested
A replicated study in 1983–1984 on two sandy beaches in Florida and Georgia, USA (Wyneken et al. 1988) found that loggerhead turtle Caretta caretta nests relocated to incubators had similar hatching success compared to eggs reburied in an on-beach hatchery. Hatching success was similar for artificially incubated eggs (135 of 163, 83% of eggs hatched) and eggs relocated to a hatchery (3,608 of 5,100, 71% of eggs hatched). An additional five nests from another beach had similar hatching success (543 of 588, 92% hatched from 5 nests) (result was not statistically tested). Nine of 50 relocated clutches (18%) were partially destroyed by ghost crab Ocypode quadrata predation, cold weather or drifting sand. In 1983, all loggerhead nests on one beach (53 nests) were relocated due to risk of total failure (predators, storm tides, poachers). Three clutches were placed in glass-fronted polystyrene incubators (38 x 38 x 19 cm) and 50 clutches were reburied in hand-dug nests in a fenced area on a nearby dune. In 1984, five nests from a second beach were relocated for artificial incubation. Hatching success was assessed following emergence of hatchlings.Study and other actions tested
A replicated, randomized study in 1986 on one sandy beach in Rantau Abang, Malaysia (Chan 1989; same experimental set-up as Chan & Liew 1995) found that relocating leatherback turtle Dermochelys coriacea eggs for artificial incubation in Styrofoam boxes resulted in similar hatching success compared to eggs that were relocated to an on-beach hatchery. Hatching success was similar for eggs from Styrofoam boxes (52–100%) and eggs from the hatchery (13–92%). In addition, careful handling of eggs during the first five days of incubation did not affect hatching success (handled eggs: 70–100%; non-handled eggs: 52–100%). Eggs were collected from four natural nests (only yolked eggs of normal size) and four groups of 23–25 eggs each were incubated in Styrofoam boxes with egg handling during the first five days; Styrofoam boxes with no handling; or in an on-beach hatchery (98 eggs/treatment). Eggs in the on-beach hatchery were buried 60 cm deep, and the nests were surrounded with chicken mesh after 50 days to capture emerging hatchlings. Half on the Styrofoam boxes were kept in a well-ventilated shed, and the others were kept in an enclosed laboratory. Hatching success was measured by counting the number of hatchlings that emerged.Study and other actions tested
A replicated, randomized study in 1986 on one sandy beach in Rantau Abang, Malaysia (Chan & Liew 1995; same experimental set-up as Chan 1989) found that relocating leatherback turtle Dermochelys coriacea eggs for artificial incubation in Styrofoam boxes resulted in all male hatchlings. Of the hatchings that were sexed, 29 of 29 were male. Eggs were collected from natural nests (only yolked eggs of normal size) and three groups of 25 eggs were incubated in Styrofoam boxes (temperature range 27–29°C). Temperatures were monitored three times/day (0900, 1200 and 1500 h) with a mercury thermometer inserted horizontally through a hole in the side of the box. A sample of 9, 9 and 11 hatchlings from each box were selected for sexing. These hatchlings were euthanised in chloroform and sex was determined by removing and examining the gonads.Study and other actions tested
A study in 1995–1996 on a sandy beach on the southeastern coastline in Virginia, USA (Cross et al. 1998) found that most loggerhead turtle Caretta caretta eggs artificially incubated in plastic planter pots with predator proof cages hatched. Hatchling success of three loggerhead turtle nests artificially incubated in plastic planter plots was 94%, 88% and 42% (numbers of eggs not provided). In 1995–1996, three late loggerhead turtle nests were relocated with their nesting chamber sand to large plastic tree planter pots (depth: 67 cm, top diameter: 76 cm) lined with burlap and damp sand (see original paper for details). Nests were covered with predator-proof nest cages and placed in enclosed heated building. Hatchlings were released on the natal nesting site for imprinting and released in the ocean.Study and other actions tested
A replicated, controlled study in 2007–2010 on 12 sandy beaches in Saona Island, Dominican Republic (Revuelta et al. 2013) found that artificially incubating hawksbill turtle Eretmochelys imbricata nests in boxes had similar hatching and emergence success compared to nests left in situ. Artificially incubated hawksbill turtle nests had similar hatching success (72–81%) and emergence success (69–80%) compared to nests left in situ (hatching success: 72–78%; emergence success: 67–72%). In 2007–2010, hawksbill turtle nesting activity was monitored on 12 beaches (0.01–2.10 km long) and nests deemed vulnerable to predation or harvesting were removed for artificial incubation in plastic boxes filled with sand and polyurethane foam (see original paper for details). Artificial incubation boxes were placed in a facility near one of the beaches (4 m long x 3 m wide) with a sand floor and wire mesh and corrugated metal walls. Hatching and emergence success was determined for clutches that were artificially incubated (20–41 nests/year, 119 total nests) and left in situ (7–21 nests/year, 49 total nests).Study and other actions tested
Referenced paperRevuelta O., León Y.M., Aznar F.J., Raga J.A. & Tomás J. (2013) Running against time: conservation of the remaining hawksbill turtle (Eretmochelys imbricata) nesting population in the Dominican Republic. Journal of the Marine Biological Association of the United Kingdom, 93, 1133-1140.
A study in 1993–2010 on four sandy beaches in a single bay in Nayarit, Mexico (Hart et al. 2014) found that at least half of artificially incubated olive ridley turtle Lepidochelys olivacea nests hatched successfully each year. Over 18 seasons of artificially incubating olive ridley turtle nests, hatching success was 50–59% in two years, 60–69% in five years, 70–79% in three years, 80–89% in six years and >90% in two years. Number of hatchlings released varied between 2,555 in 1997 and 23,467 in 2006. Four turtle nesting beaches (2–8 km long) were monitored during the peak nesting season (July–November) for two nights/week in 1993–1999 and seven nights/week in 2000–2010. Nests were collected (1.4 nests/day) and artificially incubated in polystyrene boxes (40 x 30 x 50 cm, wall thickness: 2 cm; see original paper for details) in an indoor facility on one of the beaches. Hatching success was evaluated once 20 hatchlings had emerged by calculating the proportion of live and dead neonates.Study and other actions tested
A replicated, controlled study in 2006–2010 on five sandy beaches in southwest Dominican Republic (Revuelta et al. 2015) found that leatherback turtle Dermochelys coriacea nests relocated for artificial incubation tended to have lower hatching rates than nests left in situ on a beach that was patrolled by park rangers. Results were not statistically tested. Over two years, nests relocated for artificial incubation tended to have lower hatching success (east hatchery: 51–58%; west hatchery: 34–43%) than nests left in situ (74–85%). In March–August 2008–2009, nests were relocated from three beaches in the east (35 nests) and two in the west (31 nests) of a national park (1,374 km2). On western beaches, which had limited human access, 43 nests were left in place and monitored to hatching. Eggs from relocated nests were placed polystyrene boxes with sand and moved to nearby hatcheries (one in the east, one in the west, enclosed wooden barracks with concrete floor and metal roof). On the western beaches where nests were left in situ, nightly patrols were carried out by government rangers 2–3 nights/week in April–May.Study and other actions tested
Referenced paperRevuelta O., León Y.M., Broderick A.C., Feliz P., Godley B.J., Balbuena J.A., Mason A., Poulton K., Savoré S., Raga J.A. & Tomás J. (2015) Assessing the efficacy of direct conservation interventions: clutch protection of the leatherback marine turtle in the Dominican Republic. Oryx, 49, 677-686.
A controlled study in 1979–2014 on sandy beaches in the Gulf of Mexico, Texas, USA (Shaver & Caillouet 2015) found that artificially incubated kemp’s ridley turtle Lepidochelys kempii nests had higher hatching success than nests left in situ. Results were not statistically tested. Emergence success of artificially incubated kemp’s ridley turtle nests was 82% and hatching success of in situ nests was 62%. The authors reported that many in situ nest hatchlings did not make it to the sea successfully. Over the 37-year programme, 130,847 artificially incubated hatchlings emerged successfully and were released. In 1979–2014, the majority of kemp’s ridley turtle nests laid in the USA were collected for artificial incubation (1,606 nests) and a small number hatched in situ (61 nests). Hatching rates were assessed for 26 in situ nests laid in 1979–2008.Study and other actions tested
A randomized, controlled study in 2012–2013 on sandy beaches on the pacific coast of Mexico (Hart et al. 2016) found that relocating olive ridley turtle Lepidochelys olivacea nests for artificial incubation resulted in similar hatching success, but mixed effects on hatchling size and behaviours, compared to nests moved to on-beach hatcheries. Hatching success was similar for eggs artificially incubated (89% success) and placed in beach hatcheries (82% success). Polystyrene-box incubated hatchlings had smaller straight carapace length (39 mm) and slower crawl speeds (0.01 m/second) than those from beach hatcheries (length: 41 mm; crawl speed: 0.02 m/second). Carapace width, hatchling weight and righting response time were similar between polystyrene box and beach hatchery nests (see original paper for details). Eggs from 49 nests were moved to one of two treatments: embedded in sand in polystyrene boxes (16) or buried in an on-beach hatchery (33). Upon emergence and movement, 10 hatchlings were randomly chosen from each nest (489 individuals in total) for measuring, weighing and to take part in fitness tests.Study and other actions tested
A replicated, randomized, controlled study in 2015 in laboratory conditions in Costa Rica (Williamson et al. 2017) found that olive ridley turtle Lepidochelys olivacea eggs artificially incubated in normal oxygen conditions had better hatching success, but were more vulnerable to being inverted, than eggs initially artificially incubated in low oxygen (‘hypoxic’) conditions. Hatching success of olive ridley turtle eggs initially incubated in any one of three hypoxic conditions was lower (Perspex box with nitrogen: 23 of 75 eggs; zip lock bag with nitrogen: 14 of 71 eggs; vacuum-sealed plastic bag: 34 of 79 eggs) than eggs incubated in normal oxygen conditions (53 of 78 eggs). Hatching success in hypoxic-maintained eggs was similar whether or not eggs were inverted during the incubation process, whereas when eggs were incubated in normal oxygen conditions, inverting eggs lowered hatching success (see original paper for details). For three days after collection, olive ridley eggs collected from six nesting females in October–November 2015 were either kept in normal oxygen conditions in a sand-filled incubator (78 eggs), or in one of three ‘hypoxic’ containers: a Perspex box filled with nitrogen (75 eggs), a plastic bag filled with nitrogen (71 eggs), or a vacuum-sealed bag (79 eggs; 13–24 eggs/hypoxic container, four containers/type). A subset of eggs from each treatment (normal oxygen: 10 eggs; Perspex box: 10 eggs; zip lock bag: 7 eggs; vacuum-sealed bag: 10 eggs) were inverted 180° horizontally after three days and compared to equivalent numbers of eggs/treatment that were not inverted. After experimental treatments, eggs were either buried in a hatchery or maintained in incubators and hatchlings were counted on emergence.Study and other actions tested