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G  R E E N TU R T L E A  B U N D A N C E

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What

What Is It?

BENCHMARK

Green turtles (Chelonia mydas) are one of the largest

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of the sea turtle species and are found globally in

tropical and subtropical waters. They are listed as

TA R G E T

"Endangered" on the IUCN Red List of Threatened

Species, due to worldwide population declines over

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the past three generations. (See Appendix 3). An

Endangered species is one that is believed to be

RED FL AG

facing an extremely high risk of extinction in the wild.

The abundance of green turtles may be characterized

in terms of (a) numbers of adults, or (b) numbers of

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nests.

Why Do We Measure It?

Why

These highly migratory turtles use a variety of

habitats throughout their lifetime. Adults nest on

One reason for measuring green turtle abundance is

sandy beaches; post-hatchlings, small juveniles and

simply to keep track of this threatened species. There

migrating adults roam in oceanic zones; and larger

is a great concern over the historic loss and continued

juveniles and adults forage in shallow protected

overall decline of the global green turtle population.

waters. Coral reefs or rocky outcrops near foraging

seagrass meadows are often used as day- and

The abundance of green turtles may also be a proxy

night-time resting areas. Green turtles are especially

indicator of herbivory in seagrass beds. Historically,

susceptible to population declines because of their

these turtles, whose adults feed primarily on

vulnerability to human impacts during all of their life-

seagrasses and macroalgae, have played a functionally

stages -- from eggs to adults.

important role as a dominant herbivore of shallow

seagrass meadows. The turtles help to recycle the

Among the greatest threats to green turtles in the

nutrients "locked up" in the seagrasses. By quickly

MAR are:

digesting and processing consumed grasses, turtles

· illegal harvesting of eggs and adults at nesting

make the nutrients available to other organisms.

beaches, plus the capture of juveniles and adults at

Green turtles help maintain seagrass beds and make

feeding areas; and

them more productive.

How Do We Measure It?

· degradation or loss of nesting and foraging areas

due to coastal development, dredging in seagrass

Nesting surveys are conducted at several locations in

beds, and incidental catch in fisheries.

the MAR, although methods for data collection and

Green turtle harvest is illegal in all of the MAR

reporting are not standardized regionally47. Some

countries (all of whom have signed the Inter-American

tagging studies of adults have been done, but these

Convention for the Protection and Conservation of

are often expensive48.

Sea Turtles, IAC)47. However, poaching of adults for

Many areas in the MAR may be important nursery

meat, shells and leather still occurs, along with the

and foraging areas for green turtles, including those

harvesting of eggs.

that nest outside the region. Therefore, tracking the

Extensive development in the region, particularly along

number of nests in the MAR may not suffice.

the Yucatan coast, has destroyed nesting beaches

Collaborations with marine tour guides and fishermen

and altered nearshore habitats. Increasing demand

are needed to develop a sighting frequency reporting

for coastal development and a lack of regulation and

protocol. WWF and the ICRAN MAR Alliance has

enforcement continue to be problematic.

developed one such activity using the REEF sea turtle

Another growing concern is the increasing global

identification cards49.

prevalence of debilitating tumors that are often lethal

to green turtles.

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