Protect habitat: Sea turtles

Overall effectiveness category Awaiting assessment
Number of studies: 4
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Effectiveness

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Background information and definitions

Legally protecting habitat may reduce its conversion and degradation by humans. This may in turn serve to maintain or slow the decline of the abundance and diversity of reptiles that make use of that habitat.

Assessing the effectiveness of protected areas is particularly difficult. For example, protected and unprotected areas used for comparison might start off with different quality habitats (protection often being granted to the best quality habitat). Protected areas are also more likely to be in remote areas, so less accessible to threats such as harvesting (Joppa & Pfaff 2009). Finally, effectiveness is best monitored over long timescales, but this increases the chance that other factors influence the ecosystem. The most reliable studies would compare similar quality protected and unprotected areas over time, and possibly correct for some of the biases.

Due to the number of studies found, this action has been split by species group. See here for all reptiles (excluding sea turtles).

^{Joppa L.N. & Pfaff A. (2009) High and far: biases in the location of protected areas. PLoS ONE, 4, e8273.}

Study locations

Key messages

Four studies evaluated the effects of protecting habitat on sea turtle populations. One study was in each of Costa Rica, the Seychelles, Belize and the USA.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (4 STUDIES)

Abundance (3 studies): One before-and-after study in Costa Rica found that after an area was protected, there were fewer nesting female leatherback turtles than before protection. One replicated, randomized, site comparison study off the coast of Belize found that in protected areas there were more hawksbill turtles than outside. One site comparison study in the USA found that differences in the abundance of green, loggerhead and hawksbill turtles in protected and unprotected areas were mixed.
Reproductive success (2 studies): One before-and-after study in Costa Rica found that after an area was protected, more leatherback turtle hatchlings were produced than before protection. One before-and-after study in the Seychelles found that nesting activity by green turtles increased following both habitat and species protection.

BEHAVIOUR (0 STUDIES)

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

A before-and-after study in 1988–2004 on three beaches in Costa Rica (Santidrián Tomillo et al. 2007) found that six years after a national park was created, numbers of nesting female leatherback turtles Dermochelys coriacea tended to be lower and hatchling numbers tended to be higher than before the park was created. Results were not statistically tested. In the six nesting seasons after a national park was created, 68–1,000 female leatherback turtles nested/year and 15,734–153,547 hatchlings/year were produced, compared to 732–1,504 nesting female leatherback turtles and 30,180–30,788 hatchlings/year in the three years before the park’s creation. The park was declared in 1991 and comprises three beaches. An unspecified number of nests were relocated due to threat of tidal inundation. Nesting female numbers were based on counting depressions left in the sand by nesting turtles.
Study and other actions tested
Referenced paper
Santidrián Tomillo P., Vélez E., Reina R.D., Piedra R., Paladinos F.V. & Spotila J.R. (2007) Reassessment of the leatherback turtle (Dermochelys coriacea) nesting population at Parque Nacional Marino Las Baulas, Costa Rica: effects of conservation efforts. Chelonian Conservation and Biology, 6, 54-62.
A before-and-after study in 1968–1976 and 1981–2008 on sandy beaches on an atoll island, Aldabra Atoll, Seychelles (Mortimer et al. 2011) found that legal protection for green turtles Chelonia mydas, followed by protection of the whole island 15 years later, was associated with an increase in nesting activity. Results were not statistically tested, and the effects of species and habitat protection cannot be separated. Overall nesting activity was estimated to be higher 36–40 years after turtle protection began (2004–2008: 28,200 nesting attempts/year) compared to 13–17 years after turtle protection began (1981–1985: 10,900–16,500 nesting attempts/year). The authors also reported that estimates of nesting activity around the time that turtle protection began ranged from sightings of seven females (11 day survey in 1967), to 2,000–3,000 nests/year (surveys during 1968–1970 and 1975–1976). Protection for turtles began in 1968, with the Green Turtle Protection Regulations 1968, and the atoll became a UNESCO World Heritage Site in 1983. In 1981–2008, up to 68 nesting beaches on the atoll were surveyed for turtle tracks and evidence of nesting. Survey effort varied between different years and beaches, with beaches surveyed 0–37 times/years in 1981–1994, and 4–171 times/month in 1995–2008.
Study and other actions tested
Referenced paper
Mortimer J.A., von Brandis R.G., Liljevik A., Chapman R. & Collie J. (2011) Fall and rise of nesting green turtles (Chelonia mydas) at Aldabra atoll, Seychelles: positive response to four decades of protection (1968-2008). Chelonian Conservation and Biology, 10, 165-176.
A replicated, randomized, site comparison study in 2009–2010 on an offshore coral reef atoll with two marine protected areas near Belize (Scales et al. 2011) found that hawksbill turtle Eretmochelys imbricata abundance was greater inside than outside protected areas. Hawksbill turtle abundance was greater inside protected areas (2–3 turtle sightings/hour) than outside protected areas (1 turtle sightings/hour). Hawksbill turtles were surveyed in the vicinity of a coral reef atoll (45 km long and 10 km wide) that contained six small cays and two no-take protected areas. Turtles were monitored on 49 randomly selected transects (1 km long) carried out over 30 days in April–May 2010 by three swimmers (1–20 m depths). In addition, 26 turtles were captured in April–May 2009 and in May 2010. Captured turtles were weighed and measured and a subset (10 individuals in 2009 and 9 individuals in 2010) were radio tracked every 24 hours for 6–25 days. It is unclear whether the captured turtles were included in the abundance estimates.
Study and other actions tested
Referenced paper
Scales K.L., Lewis J.A., Lewis J.P., Castellanos D., Godley B.J. & Graham R.T. (2011) Insights into habitat utilisation of the hawksbill turtle, Eretmochelys imbricata (Linnaeus, 1766), using acoustic telemetry. Journal of Experimental Marine Biology and Ecology, 407, 122-129.
A site comparison study in 2003–2012 in shallow coastal and deeper water off the coast of Florida, USA (Herren et al. 2018) found that inside a protected area there were fewer green turtles Chelonia mydas, more loggerhead turtles Caretta caretta and similar numbers of hawksbill turtles Eretmochelys imbricata compared to outside of the protected area. Results were not statistically tested. Inside a protected area, 0.1–0.6 green turtles/km, 0.2–0.5 loggerhead turtles and 0.01–0.2 hawksbill turtles were encountered compared to 1.8 green turtles/km, 0.1 loggerhead turtles/km and 0.01 hawksbill turtles/km outside the protected area. Three sites (15–27 km²) were surveyed in shallow-water habitats (0.2–6 m depths) inside a protected area (a national marine sanctuary covering 835 m² of open water and 8 km² on land) and compared to a single unprotected site (36 km²) in deeper waters (3–6 m depths). Surveys were carried out during 27 boat trips in September 2003–September 2012 (139 total survey days) by driving haphazard, non-linear transects on a boat with several observers (129 km² total area covered by surveys). Turtle sightings were recorded and where possible turtles were captured, individually-marked, weighed and measured.
Study and other actions tested
Referenced paper
Herren R.M., Bagley D.A., Bresette M.J., Holloway-Adkin K.G., Clark D. & Witherington B.E. (2018) Sea turtle abundance and demographic measurements in a marine protected area in the Florida Keys, USA. Herpetological Conservation and Biology, 13, 224-239.

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.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Reptile Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Protect habitat: All reptiles (excluding sea turtles) Action Link	Awaiting assessment	17	Synopsis Link
Retain connectivity between habitat patches Action Link	Awaiting assessment	2	Synopsis Link
Protect habitat: Sea turtles Action Link	Awaiting assessment	4	Synopsis Link