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How is the life of a marine turtle?

I have talked about marine turtles in some past posts. In concrete, about the loggerhead sea turtle (Caretta caretta). In the following weeks, I am going to talk more about this amazing marine animals. In particular, this week I will explain how is the life of a marine turtle, especially about the loggerhead sea turtle, and in the next one, I am talking about which are the threats that endanger these animals and about what we can do to save them. 

INTRODUCTION

Loggerhead sea turtle is one of the seven sea turtles on Earth. It has a worldwide distribution, being the most abundant species in the Mediterranean, and it can be identified by the presence of a carapace that measures between 80 and 100 cm long with 5 lateral scutes, so that the first of them is in contact with the nuchal scute. It is endangered according to IUCN (International Union for the Conservation of Nature). The loggerhead sea turtle feeds on jelly plankton like jellyfishes during the oceanic stage, but feeds on fishes and squids in the neritic stage. Additionally, they can consume salt water due to the presence of salt glands placed in the cranium. Like other sea turtles, it cannot hide its head and fins inside the carapace.

Claus d'identificació de la tortuga babaua (Caretta caretta) (Foto extreta de MarineBio).
Identification key for a loggerhead sea turtle (Caretta caretta) (Picture from MarineBio).

HOW IS THE LIFE OF A MARINE TURTLE?

In marine turtles, the reproductive cycles are circadian, it is that it happens regularly over the time. The periodicity depends on each species, but in the case of the loggerhead sea turtle usually is biannual, so it takes place every two years (but sometimes every three years). Anyway, this cycle is not strict because it is dependant on some factors like food availability or illnesses.

The gregarious behaviour of many species is explained for the ability to recognise the individuals of the same species. In order to recognise each other, most of the species use smell, but they can use sight and sound. During the mating, when the female accept the male, the male bites the female in the neck and in the anterior fins. The male put itself on the female and catches her with the nails of the anterior fins (in the case of the loggerhead, it has two nails per fin). Mating takes place in the sea and usually in the first hours of the day. Moreover, a female can be impregnated by several males.

Aparellament de la tortuga babaua (Caretta caretta) (Foto: OceanWide Images).
Mating of a loggerhead sea turtle (Caretta caretta) (Picture: OceanWide Images).

The moment when the marine turtles lay the eggs depend on the moon phases, tides, temperature and wind, but it usually happens during summer in sandy beaches. Females return to the beaches where they were born, coming from feeding grounds. They navigate using marine currents, temperature changes, magnetic signals and the sound and smell of the beach.

Depending on the features of the beach, this will be more or less suitable for each marine turtle species. The loggerhead prefers open and shallow beaches and bays, continental or insular, with a slope between 5-10º and with a calm swell. Moreover, these beaches have to be protected by bushes in the terrestrial part and by coral or rockery reefs in the marine part. They usually lay on the first terrace of the beach, in zones without plants and in the first attempt. All the sea turtles have in common the fact that the lay is done beyond the highest tide.

When the female finds the place, with the anterior fins do a cavity where to place its body (called bed) and next, with the posterior fins, dig out the nest and place the eggs. During the period from which the female leave the water and dig out the nest, the animal is very sensitive to bother and can stop doing the nest and come back to water. 

Sea turtles do several lays per year. In the case of loggerheads, they usually do between 2 and 4 lays per year, with 100 eggs that weights 40 grammes (this is 4 kilos per lay). Despite of this, we have to have in consideration that the number of eggs produced for a female is limited by the capacity of storage of the female, which is related with the size. Between each lay in the same reproductive cycle, the mating is not necessary because they can store sperm.

Tortuga en la fase de posta dels ous (Foto: Brandon Cole).
Turtle laying the eggs in a beach (Picture: Brandon Cole).

Eggs are incubated during 50-60 days under the sand of the beach (in the loggerhead). The hatching is synchronized and when the small turtles reach the surface in few minutes are oriented thanks to the beach slope, the sound of the waves and the light of the moon on the sea.

Cria d'una tortuga babaua (Caretta caretta) sortint de l'ou (Foto: Rewilding Europe).
Loggerhead sea turtle baby (Caretta caretta) (Picture: Rewilding Europe).

During the first days of life, turtles present a high buoyancy. In the first weeks, small turtles remain in marine currents and gyres, where food is abundant, so they have a pelagic life. If they are male, the most probable is that they will never touch the land. 

When they are born, the carapace is soft  and, for this reason, the number of individuals that will survive is just a 10% of which leave the egg due to the predators, like crabs, sharks and seagulls. During the first year only survives 10-30% of the animals. Year after year, the mortality rate decreases for the increase of size and the hardening of the carapace. A study has found that just 10 out of every 10.000 eggs will become adults and just one will die for age.

Adult de tortuga babaua (Caretta caretta) (Foto: Deviant Art).
Adult of a loggerhead sea turtle (Caretta caretta) (Picture: Deviant Art).

Sea turtles do long-distance migrations, specially in the young stage. When they abandon the beach where they were born, during the next 10 years, they will be travelling long distances. The migrations are between feeding and reproductive grounds.

Then, the cycle restarts with the newborns.

REFERENCES

  • Cardona L, Álvarez de Quevedo I, Borrell A, Aguilar A (2012). Massive Consumption of Gelatinous Plankton by Mediterranean Apex Predators. PLoS ONE 7(3): e31329. doi:10.1371/journal.pone.0031329
  • Consejería de Medio Ambiente de la Junta de Andalucía (2014). Varamientos de Especies Marinas Amenazadas. Guías prácticas voluntariado ambiental.
  • CRAM: Caretta caretta
  • Dodd, C. Kenneth, Jr. 1988. Synopsis of the biological data on the Loggerhead Sea Turtle Caretta caretta (Linnaeus 1758). U.S. Fish Wildl. Serv., Biol. Rep. 88(14). 110 pp.
  • IUCN: Caretta caretta 
  • Márquez, R (1996). Las tortugas marinas y nuestro tiempo. México: IEPSA
  • Smith, T & Smith R (2007). Ecología. Pearson Educación (6 ed.)

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