Action

Relocate nests/eggs to a nearby natural setting (not including hatcheries): Sea turtles

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (12 STUDIES)

  • Reproductive success (12 studies): Four of 12 controlled studies (including three replicated, randomized studies) in the USA, Suriname, US Virgin Islands, Costa Rica, Ascension Island, Brazil and Cape Verde found that relocated sea turtle nests had lower hatching success than natural nests in six of seven years, in 26 of 29 years, or lower hatching success than nests laid above the tidal zone, or that nests relocated >10 days after being laid had lower hatching and emergence success than natural nests or nests relocated within 12 hours. One of those studies also found that relocating nests within 12 hours had mixed effects on hatching and emergence success compared to natural nests. One study also found that two different egg collecting methods resulted in either more dead early stage or late-stage embryos. Four of the studies found that relocated sea turtle nests had similar hatching and emergence success or hatching success compared to natural nests and specifically compared to those laid in safer parts of the beach or above the high tide line. One of those studies also found that relocated nests experienced similar levels of predation by ghost crabs as natural nests. One of the studies also found that fewer relocated nests failed completely due to tidal flooding compared to natural nests. One of the studies found that relocated loggerhead turtle nests had higher hatching success than natural nests. One of the studies found that relocated leatherback turtle nests had higher hatching success compared to natural nests that were washed over by sea swells, but similar hatching success compared to natural nests that were not washed over by sea swells. The other two studies found that relocating sea turtle nests had mixed effects on hatching or hatching and emergence success compared to natural nests. One of those studies also found that in years when leatherback turtle nests were relocated, fewer were lost to erosion than when no relocations took place.
  • Condition (1 study): One replicated, randomized, controlled study in the USA found that hatchlings from relocated loggerhead turtle nests were a similar size to hatchlings from natural nests.

BEHAVIOUR (0 STUDIES)

OTHER (1 STUDY)

  • Offspring sex ratio (1 study): One replicated, randomized, controlled study in Suriname found that relocated leatherback turtle nests produced all female hatchlings, whereas 30–100% of hatchlings from naturally incubated nests were female.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated, controlled study in 1980–1982 on a sandy beach in Suriname (Dutton et al. 1985; same experimental set-up as Whitmore & Dutton 1985) found that moving leatherback turtle Dermochelys coriacea nests to above the tideline produced all female hatchlings, whereas natural nests produced mixed sex ratios and artificially incubating in Styrofoam boxes produced all male hatchlings. Leatherback turtle hatchlings reburied in the sand on the same beach produced 100% female hatchlings, compared to 30–100% of female hatchlings in natural nests and 100% male hatchlings in Styrofoam-box-incubated nests. In 1982, leatherback turtle eggs from two clutches laid below the tide line were reburied elsewhere on the beach. Ten hatchlings were randomly selected 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 five clutches in 1980 and 10 clutches in 1982 incubated in Styrofoam boxes (45–60 eggs/box).

    Study and other actions tested
  2. A replicated, controlled study in 1982 on a sandy beach in Suriname (Whitmore & Dutton 1985; same experimental set-up as Dutton et al. 1985) found that leatherback turtle Dermochelys coriacea nests reburied above the tide line had similar hatching success but lower predation rates than natural nests not washed over by sea swells. Results were not statistically tested. Average hatching success of leatherback turtle eggs reburied above the tide line was 69% compared to 33% in natural nests washed over by sea swells and 62% in natural nests not washed over by sea swells. Embryonic mortality in reburied nests was 23% compared to 35% and 13% in natural nests washed over and not washed over by swells respectively. Predation rates were 6% in reburied nests compared to 27% and 17% in natural nests washed over and not washed over respectively. Nesting turtles were surveyed <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 further up the beach above the spring high tide line (13 leatherback clutches, 50 eggs/clutch reburied together in 60 cm deep cavities 1 m apart). Relocated and natural nests (10–12 nests occasionally washed over by sea swells, 13–16 not washed over by sea swells) were excavated after emergence to evaluate hatching success.

    Study and other actions tested
  3. A replicated, controlled study in 1984 on a sandy beach in Florida, USA (Wyneken et al. 1988) found that relocating loggerhead turtle Caretta caretta nests to other locations on the beach or for artificial incubation resulted in higher hatching success compared to nests left in place (but protected from predation). Hatching success was higher for relocated nests (1,054 of 1,151 eggs, 92% hatched from 10 nests) compared to nests left in place (2,400 of 2,796 eggs, 87% hatched from 24 nests). Hatching success did not differ for relocated nests that were reburied (543 of 588, 92% hatched from 5 nests) or artificially incubated (511 of 563 eggs, 91% hatched from 5 nests). Six nests left in place were lost to the tide or vandalism. Ten nests at risk from predation or tides were reburied in another part of the beach (five clutches) or were incubated in polystyrene boxes with sand (38 x 38 x 19 cm). A further 31 nests were screened to prevent predation and left in place. Hatching success was assessed following emergence of hatchlings.

    Study and other actions tested
  4. A controlled, before-and-after study in 1981–1994 on a sandy beach in St Croix, US Virgin Islands (Boulon et al. 1996) found that relocating leatherback turtle Dermochelys coriacea nests away from erosion-prone areas lead to fewer nests being lost to erosion compared to when no nests were relocated, and variable hatching success in relocated compared undisturbed nests. Results were not statistically tested. In years when nests were relocated, 1–30% were lost to erosion (of 82–355 nests), whereas 48 of 119 (40%) were lost in the year in which no relocations took place. Hatching success was lower in relocated nests (51–69%) compared to undisturbed nests (57–76%) in 10 of 13 years. In 1982–1994, all nests in erosion-prone areas were relocated to stable parts of the beach immediately after laying. In 1981–1994 the beach was patrolled hourly between 20:00–05:00 h every night from 1st April until no new nests had not been discovered for 10 days. Nests were excavated several days following emergence to record hatching success.

    Study and other actions tested
  5. A replicated, controlled, before-and-after study in 1999–2004 on a sandy beach in Guanacaste Province, Costa Rica (Piedra et al. 2007) found that relocating leatherback turtle Dermochelys coriacea nests to safe locations on the beach or a hatchery resulted in similar hatching and emergence success compared to nests left in situ. Results were not statistically tested, and no distinction was made between nests relocated to the beach or hatchery. Hatching and emergence success were similar for relocated nests (hatching: 19–52%; emergence: 14–32%) and nests left in situ (hatching: 30–69%; emergence: 9–57%). In October–March 1999–2004, beaches were searched nightly for nesting females. In 2001–2004, nests considered to be at high risk (such as being within tidal zone, in areas of high pedestrian traffic, in vegetation or close to estuary) were relocated to safe places on the beach or a hatchery (86 nests), and others were left in situ (220 nests). Two days after emergence of the first hatchling, or 60 days after laying, nests were excavated to determine hatching and emergence success.

    Study and other actions tested
  6. A replicated, randomized, controlled study in 2006 on a sandy beach on Ascension Island (Pintus et al. 2009) found that relocating green turtle Chelonia mydas eggs from nests in the tidal zone resulted in lower hatching success compared to in situ nests laid above the tidal zone. Hatching success was lower for relocated nests (66% and 67%) compared to natural nests laid further up the beach (86%). One relocation method (collecting eggs during laying process) resulted in more early-stage dead embryos compared to in situ nests (22 vs 9/nest) and the other method (nest excavation) in more late-stage dead embryos (17 vs 7/nest). In March–April, a 1 km stretch of beach was searched for nesting females. Nests in the tidal area (doomed nests) were relocated close to one of 23 natural nests laid further up the beach (23 locations further up the beach, with 2 relocated nests and 1 natural nest/location). Eggs were relocated by excavating the nest following completion of nesting; or by removing eggs from the chamber during the laying process. After hatchling emergence nests were excavated to assess hatching success.

    Study and other actions tested
  7. A replicated, randomized, controlled study in 2005–2006 on a beach in Georgia, USA (Tuttle & Rostal 2010) found that relocating loggerhead turtle Caretta caretta nests to areas above the high-tide resulted in higher hatching success compared to nests laid above and below the high-tide that were left in place. Hatching success was higher for relocated nests (81%) than natural nests overall (above and below high tide line; 61%) but was statistically similar to natural nests laid above the high tide (72%). Overall, hatching success was higher above the high tide (79%) than below (54%). There was no significant difference between relocated and natural nests for incubation duration (relocated: 55 days; natural: 54 days) or hatchling size (relocated: 45 mm; natural: 45 mm). In May–August 2005–2006, turtle nests were randomly selected to be relocated (34 nests) or left in place (35 nests). Relocated nests were reburied above the high tide line in nests dug to match the dimensions of the original. All nests were covered with a metal screen to prevent predation. Following hatchling emergence, hatching success was determined and 20 hatchlings were selected for measuring.

    Study and other actions tested
  8. A replicated, controlled study in 2004–2011, along 100 km of sandy beach in Rio de Janeiro State, Brazil (Lima et al. 2012) found that relocating loggerhead turtles Caretta caretta nests to nearby locations on the beach resulted in lower hatching success compared to nests left in situ. Hatching success was lower for relocated nests than for nests left in situ in six of seven seasons (relocated: 57–69%; in situ: 73–81%). In addition, hatching success was also lower for nests relocated to an on-beach hatchery in six of seven seasons (61–66%) compared to in situ nests. In the nesting seasons of 2004–2011 beaches were patrolled daily, and nests were transferred to a safe location on the beach (24–172 nests/season); moved to an on-beach hatchery (231–1,015 nests/season); or left in situ (8–316 nests/season). Those nests not taken to the hatchery were covered with a wire mesh screen. After hatchling emergence, nests were excavated to assess hatching success.

    Study and other actions tested
  9. A controlled study in 2008 on a sandy beach in Boa Viste, Cape Verde (Marco et al. 2015) found that loggerhead turtle Caretta caretta nests relocated away from the shoreline experienced a similar amount of predation by ghost crabs Ocypode cursor and had similar hatching success compared to natural nests left in situ. Ghost crab predation rates were similar in nests that were relocated away from the shoreline (41%) and nests that were left in place (55%). Hatching success was also similar in nests that were relocated away from the shoreline (42% success) and nests that were left in place (33% success). Turtle nests were excavated, eggs counted and reburied in another part of the beach (20 nests) or left in the same place without any protection (20 nests). Nests were monitored daily until emergence and hatchling tracks were counted. All nests were excavated after last emergence and remaining eggs counted for analysis.

    Study and other actions tested
  10. A replicated, randomized, controlled study in 2002–2007 on two sandy beaches in Georgia, USA (McElroy et al. 2015) found that relocating loggerhead turtle Caretta caretta nests resulted in similar hatching and emergence success and fewer nests being flooded compared to nests left in situ. When accounting for nest elevation, hatching and emergence success were similar for relocated nests (hatching: 70–73%; emergence: 67%) and nests left in situ (hatching: 76–80%; emergence: 68–78%). Fewer relocated nests failed completely than in situ nests (relocated: 13 of 168, 8%; in situ: 44 of 212, 21%; not statistically tested) and more relocated nests avoided tidal flooding (relocated: 94–98%; in situ: 71–81%; not statistically tested). Two stretches of beach (3 and 7 km) were searched daily during May–October 2002–2007. Nests were either relocated to the top of a nearby dune (85 with a plastic screen; 83 no screen) or were left in situ (75 screened; 137 with no screen). Data from 2004 were excluded due to tropical storms. Nests were excavated five days after hatchling emergence began and the numbers of hatched and unhatched eggs and live or dead hatchlings were counted.

    Study and other actions tested
  11. A controlled study in 2007 on a sandy beach in Florida, USA (Ahles & Milton 2016) found that relocating loggerhead turtle Caretta caretta nests more than 10 days after being laid reduced hatching and emergence success. Loggerhead turtle nests relocated >10 days after being laid had lower hatching (52%) and emergence success (47%) compared to nests relocated within 12 hours to native sand (hatching success:79%; emergence success: 68%) or restored beach (hatching success: 90%; emergence success: 87%), or compared to nests left in situ (hatching success: 85%; emergence success: 84%). Nests relocated within 12 hours to restored beach and native sand had statistically similar hatching success to nests left in situ, but emergence success of nests relocated to native sand was statistically lower than nests left in situ or relocated to restored beach. In May-June 2007, as part of post-storm beach restoration, 12 loggerhead turtle nests (1,429 eggs) were moved 10–38 days after being laid to a section of the beach with native sand. All new nests that were laid in the restoration zone were moved within 12 hours of deposition to native sand beach (63 nests; 7,563 eggs) or restored beach (43 nests; 5,155 eggs). Nests laid on the beach after restoration was complete were left in situ (86 nests; 9,921 eggs). All nests were monitored for hatching and emergence success.

    Study and other actions tested
  12. A replicated, controlled study in 1982–2010 on a sandy beach in St Croix, US Virgin Islands (Garner et al. 2017; continuation of Boulon et al. 1996) found that relocated leatherback turtle Dermochelys coriacea nests had lower hatching success than nests left in situ in 26 of 29 years. In 1982–1994, hatching success was lower in relocated nests (51–69%) compared to undisturbed nests (57–76%) in 10 of 13 years (result not tested statistically). In 1995–2010, hatching success was lower in relocated nests (37–66%) than nests left in situ (43–69%) every year. In 1982–2010, all nests in erosion-prone areas were relocated to stable parts of the beach immediately after laying. The beach was patrolled hourly between 20:00–05:00 h every night from 1 April until no new nests had been discovered for 10 days. Nests were excavated several days following emergence to record hatching success.

    Study and other actions tested
  13. A replicated, controlled study in 2016 on one sandy beach in Alabama, USA (Ware & Fuentes 2018) found that relocating loggerhead turtle Caretta caretta nests higher up the beach resulted in similar hatching success, but lower emergence success compared to undisturbed nests. Hatching success was similar for relocated (66%) and undisturbed nests (66%), but relocated nests had lower emergence success (relocated: 76%; undisturbed: 84%). Seven measures of flooding and wave wash-over were similar at the locations of relocated nests, original nest locations and undisturbed nests. In May–August 2016, twenty nests discovered 0–22 m from the high-tide line were relocated higher up the beach. Seventy-four nests (3–50 m above high-tide line) were left undisturbed. Nest locations were monitored for up to 75 days and the fate of eggs was checked three days after hatchling emergence, or 75 days after laying occurred.

    Study and other actions tested
Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

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Reptile Conservation

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