LESSON 2: SEA TURTLE LIFE CYCLE
A. NESTING BEACHES: ADULT FEMALE
During nesting season, females come to the beach to lay eggs within a few weeks of
mating. After making their way to the beach, they use their front flippers to dig a large
depression called a “body pit,” using such force that they send sand flying through the
air. Females then use their back flippers to dig a smaller hole at the far end of the body
pit called an “egg chamber,” into which they deposit between 50-200 soft-shelled eggs,
depending on the species. These eggs are usually the size of a ping-pong ball. After
refilling and covering their nests with sand, they return to sea.
B. ADULT FEMALES RETURN TO FEEDING AREAS AFTER NESTING SEASON
Depending on the distance, this journey may take several months. Females must return
to feeding areas – generally nearshore areas – after each nesting season to replenish
her energy for the next nesting season. This period typically takes more than a year, and
in many cases, several years. Other adults (females and males) and large juveniles also
feed in these areas.
C. HATCHLINGS TO OCEAN AND EARLY YEARS IN OPEN OCEAN HABITAT
When fully developed, hatchlings break through their eggshell and slowly dig their way
to the surface, typically all together. This process can take a few days.
Hatchlings generally wait until night to head for the ocean, when they can use the cover
of darkness to avoid detection by many predators on the beach and in the water.
After reaching the water, hatchlings enter into a multi-day "swimming frenzy," during
which they swim almost continuously, fueled only by leftover egg yolk, to reach deeper
water away from shore. Little turtles are transported by strong ocean currents to openocean (oceanic) habitats, where they live in Sargassum mats (brown algae), and have an
omnivorous diet. This oceanic stage can last from a few years to decades. Leatherbacks
are the only species that spend the majority of their life in this oceanic environment;
flatbacks are the only species that lack this open ocean stage entirely.
D. DEVELOPMENTAL MIGRATIONS TO NEARSHORE FEEDING AREAS
After this oceanic period, the juvenile turtles move into highly productive near shore
feeding areas to finish growing, a process that can take as little as a few years and as
long as a few decades. While these feeding grounds tend to offer a greater abundance
and variety of food than the open ocean, they also tend to host more predators. Thus,
young turtles wait to enter these areas until they have attained a larger body size, which
helps them avoid being eaten. Adult turtles also occupy near shore feeding areas. Adult
turtles remain in these areas until they have accumulated enough energy reserves to go
to breeding areas for reproduction. This period typically takes more than a year, and in
many cases, several years.
E. MIGRATION OF ADULTS TO NATAL BEACHES FOR MATING
After acquiring sufficient resources, adult males and females migrate to breeding areas
to mate and, in the case of females, to nest.
The distance between feeding and breeding areas can be hundreds, to tens of
thousands, of kilometers. Each nesting season, most females return to nest at the same
beach, or group of beaches, where they were born as hatchlings. This is called natal
homing.
F. MATING IN COASTAL AREAS NEAR NESTING BEACHES:
Although a female typically only need mate with one male to obtain enough sperm to
fertilize all of her eggs in a season, multiple paternity is common in sea turtles. This is
most likely due to the fact that male sea turtles generally attempt to mate with as many
females as possible. Males are quite aggressive during the mating season, both with
other males and with females.
G. ADULT MALES RETURN TO FEEDING AREAS
Like females, male turtles show natal homing, but visit broader areas and more sites
than females do. Males will try to mate with as many females as they can during a
season. Once males have mated and are unsuccessful in finding more mates, they return
to their feeding areas.
H. INTERNESTING HABITATS
Females stay near their nesting beach during the nesting season, which can last one to
two months. Depending on the species, female turtles lay between two and seven
clutches (a group of eggs deposited during one egg-laying event), in a season – one
clutch every 10 to 15 days. Olive ridley and Kemp’s ridley turtles are the exceptions to
this pattern when they nest in arribadas, or synchronized mass nesting events, that
occur over a three to seven-day period once a month.