MARE 101L Green Sea Turtle Survey Lab Summer 2013
Name: __________________
Lab report is due Wednesday, July 3rdth at 8:00am. You may e-mail it to Dr. Turner at
jpturner@hawaii.edu.
Today’s Exercise
Conduct snorkel surveys for Green Sea Turtles in East Hawaii
When you find a turtle swim slowly towards it and try to take a few photos for identification.
You should then estimate the size of the animal and the tumor score while making notes on the
turtle ID form. You should note any injuries, tumors, shell deformities, etc. Then summarize the
data on the Turtle Survey form on the other side of the slate. Take pictures of the slate between
turtles so that you can match up drawings with pictures later. Have fun!
Make sure you answer the question at the bottom of the page and turn them in no later than
Wednesday, July 3. You only need to turn in this page. You can save the background
information for yourselves.
Questions
1. How many turtles did you identify at each location?
2. What was the breakdown of turtle sizes at each location?
3. How many turtles were tumored at each ocation?
4. Did you see any relationship between tumors and turtle size? Were larger turtles more
tumored or smaller ones?
5. What would be your recommendations for turtle survey work based upon this lab in order to
effectively assess turtle tumors in Hawaii?
Background Information
The green turtle is listed as endangered by the International Union for the Conservation of
Nature. In 1978, the Hawaiian population of the green turtle was listed as threatened under the
U.S. Endangered Species Act of 1973.
Green turtles were a source of food, tools, and ornamentation for early Hawaiians. With the
arrival of western culture, however, the level of exploitation of this resource increased
dramatically. Large numbers of green turtles were harvested throughout the Hawaiian Islands
through the nineteenth and early twentieth centuries. In 1974, the State of Hawaii finally passed
a regulation providing some protection, but this was virtually ignored until 1978, when the
Hawaiian green turtle was placed on the list of threatened species.
In other parts of the world, green turtles face a serious threat from the destruction and loss of
nesting sites. Fortunately, over 90% of nesting activity for the Hawaiian green turtle population
occurs at the French Frigate Shoals, inside a National Wildlife Refuge System administered by
the U.S. Fish and Wildlife Service. This, combined with its threatened status under the U.S.
Endangered Species Act, has created an environment in which the Hawaiian green turtle should
prosper. Unfortunately, the Hawaian green still faces severe threats, most notably fibropapilloma
tumors and degradation of foraging habitat. Current Hawaiian green turtle population levels are
still thought to be below pre-western contact and probably pre-World War II levels as well. In
1992, the estimate of mature female green turtles associated with the French Frigate Shoals was
set at roughly 750.
Description
The green sea turtle is the largest hard-shelled sea turtle. Adults of this species commonly reach
100 cm in carapace length and 150 kg in mass. The average size of a female nesting at the
French Frigate Shoals was reported in 1980 to be 92 cm straight carapace length, with an average
body mass of 115 kg. This is somewhat smaller than her Atlantic cousin.
Hatchling green turtles weigh about 25 g and have a carapace about 50 mm long. Hatchlings are
black on top and white underneath. The plastron of the Hawaiian green turtle becomes orange or
yellowish orange, and the carapace remains predominantly black with various shades of olive
and yellowish gold forming swirls and irregular patterns on their shells. A small number of adult
females (perhaps 3%) possess predominantly brown carapaces, with patterns of yellow, gold, and
reddish brown.
Growth
Growth rates of pelagic-stage Hawaiian green turtles (during their Lost Years) have not been
measured under natural conditions, since contact with them is extremely rare. Growth rates of
juveniles, sub-adults, and adult turtles measured by George Balazs at seven resident sites in the
Hawaiian Archipelago revealed substantial variation. Along the Kau coast of the island of
Hawaii, annual growth was approximately 4.50 cm to 6.25 cm. At the French Frigate Shoals,
annual growth ranged from approximately .25 cm to 1.50 cm. These differences are probably a
function of food availability and quality.
Based on growth rate measurements, George Balazs estimates the age of the Hawaiian green
turtle at sexual maturity can range from 11 to 59 years.
Habitat
Hawaiian green turtles occupy three habitat types:
1) Nesting and basking beaches, almost exclusively in the French Frigate Shoals.
2) Convergence zones in the pelagic habitat.
3) Benthic feeding grounds in relatively shallow waters.
Females deposit egg clutches on beaches in the French Frigate Shoals, digging a deep nest cavity
above the high water line. Eggs incubate for approximately 65 days before hatching. Hatchlings
leave the beach and apparently move into convergence zones in the open ocean where they spend
an undetermined length of time. Hawaiian green turtles reach a carapace length of approximately
35 cm, about 10 cm larger than juveniles of other green turtle populations, before leaving the
pelagic habitat and entering benthic feeding grounds.
In Hawaii, there is a wide variety of feeding habitat. For example, Balazs reports observations of
feeding behaviour along the Kau coastline of the island of Hawaii. This is a lava coast with few
protective reefs, and most foraging occurs under turbulent conditions. He also reports
observations of foraging at Bellows Beach, Oahu, which has a sandy bottom extending 25 to 100
m from shore and subtidal reefs protecting the coastline from heavy surf.
One interesting behaviour of the Hawaiian green turtle is its fondness for crawling ashore at
isolated sites in order to bask. Basking is rare among marine turtles, and has been observed in
only a few populations in the Pacific. Hawaiian green turtles bask, but this behaviour seems to be
limited to the Northwestern Hawaiian Islands. It is thought that they do this for thermoregulation
(they like to warm up in the sun), resting (they like to sleep in the sun), and perhaps for
protection from tiger sharks (they don't like to be eaten).
Diet
Scientists assume that post-hatchling, pelagic-stage green turtles are omnivorous, but there are no
data on diet from this age class. Our personal experience with juvenile Hawaiian greens that
appear to have just arrived inshore supports this theory. Our first turtle encounter resulted when a
juvenile swam up to us and attempted to take some of the cuttlefish we were using to attract eels
for photographs. We have since observed juveniles eating sponges and seaweed, as well as
jellyfish.
Scientists do know that once green turtles shift to benthic feeding grounds, they are almost
exclusively herbivores. They feed on both seagrasses and algae. In Hawaii, there is only one
form of seagrass, Halophila hawaiiana, but this angiosperm is not common in Hawaii and is not
a major food source. George Balazs identified nine species of algae (out of approximately 400 in
the Islands) as the principle foods of the Hawaiian green turtle.
Reproduction
Female green turtles emerge at night to deposit eggs, the process taking an average of two hours.
Up to seven clutches are deposited at 12 to 14 day intervals, but the average is probably two or
three clutches. Accurate counts of the number of clutches per season are difficult to get. The
average clutch size is 100-110 eggs.
It is uncommon for females to produce clutches in successive years. Usually 2, 3, 4 or more
years intervene between breeding seasons. Mating occurs in the water off the nesting beaches.
Little is known about the reproductive biology of males, but evidence is accumulating that males
migrate to the nesting beach every year.
One interesting discovery in recent years is that incubation temperatures determine the sex of
hatchling turtles. In 1985, Standora and Spotila reported this effect on green turtles. Eggs
incubated below a pivotal temperature--which might vary among populations--produce primarily
males, and eggs incubated above this temperature produce primarily females.
The hatching success of undisturbed nests is typically high. The Hawaiian green turtle enjoys the
benefits of a protected and isolated nesting habitat and low levels of predation. Unlike many
nesting areas throughout the world, there are no nest-raiding predators (not even humans) in the
French Frigate Shoals. Ghost crabs prey upon hatchlings, but estimates of losses to crabs do not
exceed 5%. Unlike other nesting beaches throughout the world, hatchlings are not greeted by
predatory birds, and the loss to carnivorous fishes does not appear to be significant. Hatchlings in
the French Frigate Shoals do not suffer from human interference either; there are no distracting
lights from developments and no destructive beach activities.
Movements
The navigation feats of the green turtle are well known, but poorly understood. We know that
hatchlings and adult females on the nesting beach orient toward the ocean using light cues. For a
long time, no one knew what cues were employed in pelagic movements, in movements among
foraging grounds, or in migrations between foraging grounds and nesting beaches. Recently
published work, however, has suggested that the earth's magnetic field plays a role in these feats.
Hawaiian green turtles nest in the isolated French Frigate Shoals, but forage throughout the
entire Hawaiian Archipelago, a range of 2450 km. Tagging has indicated that most Hawaiian
green turtles seem to settle at a specific foraging ground and leave only to reproduce. Our
observations at Honokowai strongly support this theory, since we have seen the same core group
of animals every year since 1989.
It has been generally accepted, but not proven, that green turtles return to nest on the beach
where they were born. Green turtles do exhibit strong site-fidelity in successive nesting seasons.
Threats
The Hawaiian green turtle is fortunate that it shares only some of the same threats that menace
all marine turtles, as described in Threats To Marine Turtles. The Hawaiian green does not face
most of the common threats to turtle nests and nesting beaches. Some of the common threats are
still present: possible ingestion of marine debris and now, bad law. The most serious threats to
the Hawaiian green turtle, however, are the fibropapilloma tumor and the rapid deterioration of
its foraging sites.
Hawaiian Green Turtle Quick Facts
 Hawaiian green sea turtles are listed as threatened.
 Found throughout the Hawaiian Archipelago, a range of about 2450 km
 A gentle vegetarian, feeding almost exclusively on algae
 The most valuable of all reptiles, they were once killed for their skins, calipee, meat and
shells, but are no longer hunted in Hawaii
 In parts of Hawaii (Honokowai) more than 90% of the green sea turtles are afflicted with
fibropapilloma tumors
 The largest of the hard-shelled marine turtles: common adult weight of 115 kg and length
of over 90 cm
 Hatchlings: 4-5 cm in length
What Are Fibropapilloma Tumors?
In humans, a papilloma tumor is a benign growth that is spread by a virus. One example is the
ordinary wart. Other mammals also develop papilloma tumors, and scientists have noted many
similarities and varieties.
When papilloma tumors develop predominant fibrous tissue, they are called fibropapillomas.
Green sea turtles develop fibropapillomas that appear as lobe-shaped tumors. These tumors can
infect all soft portions of a turtle's body. Tumors grow primarily on the skin, but they can also
appear between scales and scutes, in the mouth, on the eyes, and on internal organs.
The lesions are small at first, but they can grow to 10 cm or more in diameter. In the turtles we
have observed since 1989, the early stages of the disease have followed a predictable pattern.
First, the turtle developed suspicious white spots on its body, most often around the neck and
shoulders. We refer to this as "salt and pepper" because the appearance is not unlike what you
would get if you took a salt shaker and salted a turtle.
Within a year, these white spots usually developed into full blown tumors. The disease
frequently affects the eyes first, but we have seen tumored turtles with clean, healthy eyes, so
this is by no means a rule.
The course of the tumors can vary greatly among individuals. We have seen turtles develop a
mild case that changes little from year to year. We have even seen what appears to be regression
of tumors--but this is not the norm.
Most of the turtles we have observed with the disease steadily worsen. Tumors increase in both
number and size. Particularly gruesome are tumors that develop along the neck of turtles. Picture
roughly two dozen tumors the appearance and texture of "horse apples" stuck to a turtle's neck,
and you have an excellent idea of what a stricken turtle looks like.
For whatever reason, the disease runs rampant in the juvenile turtles we observe. From "salt and
pepper" to emaciation can be as little as two years. In adults, the disease is less predictable. We
have seen everything from one turtle who had a mild case and recovered completely to another
who was weak and emaciated within four years.
What Causes the Tumors? How are They Spread?
The sad truth of the matter is that scientists aren't yet certain what causes fibropapilloma tumors
or how they are spread.
There is a lot of research being conducted to answer these questions, and while progress is being
made, so far there are no definitive answers. Because papilloma tumors are spread by a virus in
other animals, it is quite likely that a virus is the culprit in green turtles. Recent research has
strongly indicated that a herpesvirus might be the culprit, but more work is needed to decide the
issue. Unfortunately, money is hard to get, making it difficult to fund the kind of sustained
project that would have the best chance of succeeding.
It is also not clear how the virus, if a virus is indeed the cause, infects the turtles. Infected turtles
have remained in close contact with clean turtles in captivity for years without spreading the
disease to them. This suggests a carrier that is present only in the wild, but attempts to find such
a carrier have not yet been successful.
Another unexplained mystery is why the disease has reached epidemic proportions in Hawaii,
Florida, and Barbados simultaneously. Since green turtles have been known to range quite far, it
is possible that the outbreaks in Florida and Barbados are somehow related, but this cannot
explain the problem in Hawaii.
There have also been attempts to discover whether pollutants could be a factor. So far, studies
have been unable to find any unusual concentrations of pollutants in the afflicted populations.
It is possible that the disease is the result of a combination of factors. For example, turtles under
stress from pollution could be more vulnerable to a virus that would otherwise be relatively
harmless. Again, thus far research has not been able to find such a relationship.
While considerable effort has been expended in understanding the cause and spread of
fibropapilloma, it is none the less quite frustrating that there is still so much we do not know.
Impact
For the turtles, tumors, even small ones, mean they become the target of saddleback wrasses and
whitespotted tobies at the cleaning station. These fish inflict painful bites directly on the
fibropapilloma, apparently eating parasites that infest the tumors. Afflicted turtles are often
forced to leave a cleaning site prematurely. Over time, their tumors worsen and their time at
cleaning stations becomes shorter and shorter.
A thick coat of algae develops on their shells, and even on their skin. Tumors increase in number
and size, resulting in more drag and making swimming more difficult, often grow to cover both
eyes, and in the corners of the mouth where they make breathing and eating difficult.