Action

Head-start wild-caught reptiles for release: 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 (6 STUDIES)

  • Abundance (1 studies): One replicated, before-and-after study in the USA found that over the course of a 37-year head-start programme, the number of kemp’s ridley nests laid on the Texas coastline increased from near zero to 119.
  • Reproductive success (2 studies): Two studies (including one replicated, before-and-after study) in Mexico and the USA found that all 11 head-started Kemp’s ridley turtles bred in the wild following release and head-started turtles that were allowed to crawl to the sea before recapture began laying nests on their beach of origin 10–12 years after release.
  • Survival (4 studies): One of four studies (including two replicated and two controlled studies) in the Caribbean Sea, Torres Strait near Australia, Gulf of Mexico and Japan reported that all 11 head-started Kemp’s ridley turtles survived at least 11–19 years following release. Two of the studies reported that 1–16% of sea turtles were recaptured 10–27 month or 0.5–13 months following release. The other study found that four head-started hawksbill turtles survived at least 4–9 days, and one survived at least 10 months following release.
  • Condition (1 study): One replicated study in Thailand found mixed effects of tank depth on growth rate, size and body condition of green turtles during a head-starting programme and no effect of feed type.

BEHAVIOUR (2 STUDIES)

  • Use (1 study): One replicated study in the Caribbean Sea reported that one head-started green turtle travelled 2,300 km from its release location, whereas other recaptures were within 1–14 km of the release site.
  • Behaviour change (1 study): One replicated study in the Caribbean Sea found mixed effects on swimming behaviour of released head-started loggerhead turtles at 1.5 years old compared to 2.5 years old.

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 study in 1967–1974 in pelagic waters in the Caribbean Sea near Bermuda (Burnett-Herkes 1974) found that some head-started and some accidentally-caught immature green turtles Chelonia mydas survived at least several months after release in the wild. In total, 16 of 108 (15%) released head-started or accidentally-caught immature green turtles were recaptured. Nine turtles were recovered within 10 months, other recaptured turtles had spent up to 27 months in the wild. Most turtles were recaptured a few hundred metres to 14 km away from their point of release, except for one head-started turtle that was recaptured 2,315 km away from the release site after 10 months. In 1967–1971, eighty-nine green turtles were head-started in Costa Rica and released after approximately two years on the north and south coasts of Bermuda. In addition, 19 wild-born immature green turtles caught accidentally by local fisherman were tagged and released as part of the same programme.

    Study and other actions tested
  2. A replicated study in 1974–1975 in pelagic waters on the Torres Strait, northern Australia (Kowarsky & Capelle 1979) found that a small number of released head-started juvenile green Chelonia mydas and hawksbill Eretmochelys imbricata turtles were recaptured in the first year after being released. In total, 12 of 1,082 head-started green turtles and 2 of 53 head-started hawksbill turtles were recaptured 12–400 days after being released. All green turtles recaptured were released from one island, two had been released in April–June and 10 had been released in August–October. Turtles had travelled 70–570 km from their point of release. Green and hawksbill turtles were collected as eggs and hatched in captivity or as newly emerged hatchlings. Turtles were kept in captivity and were at least 1–2 years old prior to release in March–October 1974 from different islands (1,082 green turtles released in four cohorts from three islands and 53 hawksbill turtles released in one cohort from one island). Turtles were tagged prior to release. Details of monitoring were not provided.

    Study and other actions tested
  3. A replicated study in 1994–1996 in offshore waters in the Caribbean Sea near the islands of Curaçao and Klein Curaçao (Nagelkerken et al. 2003) found that released head-started loggerhead turtles Caretta caretta swimming speeds and rest frequency were similar between 1 and 2.5-year-old released turtles, but older released turtles dived more often. Swimming speed and rest frequency was similar between 1–1.5-year-old released head-started loggerhead turtles (speed: 0.4–0.7 m/second; rest frequency: 0–0.8 rests/hour) and 2.5-year-old released head-started turtles (speed: 0.3–0.9 m/second; rest frequency: 0–1.0 rests/hour). Younger turtles dived less frequently than older turtles (1–1.5-year-old: 0–2 dives/hour; 2.5-year-old: 0–4 dives/hour). In August 1993, loggerhead turtle hatchlings from a single nest were collected and reared in captivity in an aquarium for up to 2.5 years. In 1994 (13 individuals, 1–1.5-years old) and 1995–1996 (10 individuals, 2.5-years old) turtles were released onto one of four beaches and allowed to crawl to sea. Turtles were radio tagged and their swimming behaviour was observed from a boat. Turtles were tracked for 45–243 minutes post release (19 individuals).

    Study and other actions tested
  4. A controlled study in 1997–2006 in nearshore waters in the Gulf of Mexico, Mexico and USA (Shaver  & Rubio 2008) found that some released head-started female Kemp’s ridley turtles Lepidochelys kempii survived at least 11 years, nested in the wild and showed similar movement patterns to wild turtles. Eleven female head-started Kemp’s ridley turtles were found to have survived 11–19 years in the wild and bred. The authors reported that post-nesting movements and habitat use of the head-started turtles and wild female turtles were similar (data and details of statistical analysis not provided, see original paper for details). Twenty-eight female Kemp’s ridley turtles were radio tagged after nesting between 1997 and 2006. Three–six turtles were monitored each year for 9–841 days (5–563 location points/individual). Eleven turtles were released, head-started individuals (two were originally imprinted on Mexico beaches, 9 on Padre Island) and 17 turtles were wild. Head started individuals were reared in captivity for 9–11 months (10 individuals) or 3 years (1 individual) prior to release.

    Study and other actions tested
  5. A controlled study in 2005–2006 off the coast of an island in southwestern Japan (Okuyama et al. 2010) found that released head-started hawksbill turtles Eretmochelys imricata were tracked for several days after release. Four head-started turtles were tracked for 4–9 days, and a fifth turtle was tracked intermittently for 10 months. An additional five wild-caught turtles (held in captivity for 4 months) were tracked for 2–8 days, and two were recaptured 182–199 days after release. Head-started turtles either moved in random directions (four turtles) or stayed at the release site (one turtle), and wild-caught turtles tended to return to their original points of capture. Turtle eggs were collected from a nesting beach on the island and artificially incubated (29°C; >90% humidity), and hatchlings were reared for 2.5 years. An additional five wild turtles were captured and held in captivity for four months. All turtles were fitted with radio transmitters and released in April 2005 following 1 h sea-acclimation in an enclosure net (4 × 4 × 5 m). Turtles were tracked using 12 fixed receivers deployed on the ocean floor (18 m deep).

    Study and other actions tested
  6. A replicated, before-and-after study in 1978–2014 on sandy beaches in Texas, USA (Shaver & Caillouet 2015) found that some released female head-started kemp’s ridley turtles Lepidochelys kempii, that were ‘imprinted’ by allowing them to crawl to the sea before bringing them in to captivity, returned to nest on or near to the beach that they had been imprinted on at least once. In 37 years, 125 of 916 (14%) nests were laid by 53 different head-started female Kemp’s ridley turtles on the beaches where they were imprinted (turtle ages: 10–26 years old, from 12 release cohorts). The first head-started kemp’s ridley turtle nests were documented 10–12 years after the nesting females were released and 19 years after the head-start programme began. Over the 37-year programme, 9,204 hatchlings laid by imprinted head-started turtles were released and Kemp’s ridley turtle nest numbers laid on the Texas coastline increased to 119 nests in 2014, from near zero in 1979 (nest numbers fluctuated, see original paper for details). In 1978–2000, approximately 22,507 Kemp’s ridley turtle eggs were artificially incubated (1,000–2,000 eggs/year). After emergence, hatchlings were released on one of two beaches and allowed to crawl to the sea (‘imprinted’), and collected again for head-starting. In 1979–2001, imprinted, individually-marked, head-started turtles were released after 7–33 months in captivity (~23,853 imprinted head-starters released in multiple locations). Head-started nesting females were surveyed in 1986–2014 by beach patrols and satellite tracking. Eggs from all known turtle nests in the USA were collected for artificial incubation until 2014 (1,667 total nests; nesting turtles examined in 916 nests).

    Study and other actions tested
  7. A replicated study in Thailand (Songnui et al. 2017) found that captive-reared green turtles Chelonia mydas all survived for an eight-week period, and that two of five measures of growth were affected by water depth but not feed type. Survival over an eight-week period was 100%. Final body weight and growth rate were higher in tanks with shallower water (15 cm depth: body weight 107–110 g, growth 2.7–2.8% body weight/day; 30 cm depth: body weight 98–106 g, growth 2.5–2.7% body weight/day), but were not affected by feed type. Body condition, and shell size were similar across all treatments (see paper for details). One hundred and twenty turtle eggs were collected from a single female as part of a head-starting programme, and 103 hatchlings were reared in fibreglass tanks (1.5 m x 0.8 m x 0.8 m) in 15 cm of sea water for 20 days. Turtles were then moved in groups of five to tanks (0.6 x 30 m) with 15 or 30 cm deep water and provided with floating or sinking food pellets (exact number of individuals/treatment not provided).

    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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Reptile Conservation
Reptile Conservation

Reptile Conservation - Published 2021

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