Why are sea turtles threatened?

Last week, we saw with detail how is the life of a sea turtle. Did you miss it? So, click here to read it! This week, I am still talking about his amazing animals, but I am focusing on the dangers that are threatening them, both natural or anthropic, and which actions we can do to save them. 

NATURAL THREATS 

Sea turtles are threaten by natural and anthropic dangers. Natural threats include egg loss due to the inundation or erosion of the beach, predation at all life stages, extreme temperatures and disease.

Egg loss

High tides and storms can produce the egg loss for several reasons: the drowning of the eggs, the beach erosion or accretion or nests are washed away. Moreover, there are some animals that feed on sea turtle eggs.

There are several reasons that explain the egg loss (Picture: PaddleAndPath).

Predation on turtles

Despite little turtles usually leave the nest at night, the risk of being eaten by a predator is not zero, since they are part of the diet of raccoons, birds, crabs, sharks and other fishes. Young and adult turtles are also feed by some animals, like sharks and other big fishes, but the impact is not as big as in the first stages. Read the post of the last week if you want to know how many turtles die of old age for each 10.000 eggs. The number will shock you!

Crabs eat the hatching turtles (Picture: Gnaraloo Turtle Conservation Program, Creative Commons).

Hypothermia

Below 8º to 10ºC, turtles become lethargic and buoyant until they float at the surface (this condition is known as cold-stunning). At temperatures below 5º to 6ºC death rate can be important.

Diseases

Parasitic infections are common in sea turtles. Up to 30% of the loggerhead sea turtles in the Atlantic ocean have trematodes that infect their cardiovascular system. These infections, at the same time, reduce their immunological defences and then may be infected by bacteria (like Salmonella or E. coli).  Dinoflagellate blooms are also a threat for them because of the poisonous content produce health problems.

ANTHROPIC THREATS

Four are the main anthropic threats for marine turtles: egg and turtle poaching, destruction of nesting beaches, pollution and fisheries by-catch. Here, we will see some more.

Poaching

Fortunately, poaching is not present all over the world, but it can be specially important in some countries. Turtles are hunted for their meat and cartilage or for their shells (used in jewellery and like a decoration). Egg collection is also present.

Sea turtles confiscated by Philippine Police (Picture: Mongabay).

Sale of sea turtle eggs (Picture: OceanCare).

Destruction of nesting beaches

The building of infrastructures to protect ocean front property produce that females cannot access to nesting beaches and, moreover, produce their erosion. Beach nourishment to fight against beach erosion also affect them because the new beach buries the nests, offshore dredging kills them, beaches may become too compacted for nesting and steep and sand can have different properties (what may reduce, for example, gas diffusion). Tourism also affect them.

Pollution and garbage

It is not completely known if the pollutants, such as fertilizers and pesticides, have a direct impact on sea turtles, but among indirect effects there are the habitat degradation, considering that excess nutrients increase harmful algal blooms.

Garbage is also a problem. Turtles with plastic in the stomach have been found because they confuse plastic bags with jellyfishes, what block intestines and produce their death. Not only are plastics ingested, but also do they become entangled in debris like nets, fishing line or other plastic items. This produces a growth deformation.

The ingestion of plastic blocks their intestines and produce death (Picture: Fethiyetimes).

Fishing by-catch

Sea turtles are also threaten by fishing by-catch.

Drift fishing, although is forbidden in Spain, are still used and every year, each boat produce the death of a hundred animals.

The longline fishing has an important impact. In Spanish waters, every year, are captured between 15,000 and 20,000 individuals. Despite they return alive to the ocean, they have a hook in the mouth and produce post release death for the wounds. Here you can read a review of the methods to reduce by-catch on loggerhead sea turtle in longline fishing. 

Longline fishing captures between 15,000 and 20,000 individuals in Spanish waters each year (Picture: Phys).

Mortality in trawling depends on trawl times: mortality increased from 0% with times less than 50 minutes to 70% after 90 minutes. This is explained by the breathing capacity of the animals.

Global change

Ocean acidification due to the continued release of carbon dioxide may have an important impact on sea turtle populations because the quality of the food will probably reduce.  The sea level rise will have a negative impact on sea turtles because endanger the existence of beaches. Moreover, the increase in the temperatures will affect the growth and the sex ratio, since sex depends on the temperature in reptiles: below 29ºC prevail males and above, females.

HOW CAN WE HELP THEM?

• Avoid any activity or behaviour that can annoy sea turtles. In the case of feeling annoyed, you will observe that they try to leave the area, they do a fast diving and they do abrupt swimming movements.
• Reduce the speed of the ship if you see any element that could be a sea turtle. In the case of being a turtle, avoid any manoeuvre that can endanger them.
• Pick up fishing gear or garbage present in the water.
• In the case of the animal being in danger, first, call the emergency phone of your country. In the case of Spain, call 112. However, there are some actions that you can do while vets arrive:
  • Turtle with a broken shell or open injuries: cover the injuries with a wet rag with iodine (never in the eyes, ears and nose).
  • Drowned turtle: maintain the animal for 5 minutes with the ventral part face up and with the body inclined (head downwards), moving its fins.
  • Turtle with plastics in the mouth: remove the plastic taking care and call the emergency number.
  • Dead turtle: don’t touch the animal and call emergencies.
  • Hooked turtle: don’t stretch the hook and cut the line with 30 cm.
• Inform the proper authority of the location of possible nests. Some clues:
  • Tracks of turtles in the sand of the beach, with a shape of a V, with the nest in the vertex.
  • Depression in the sand, what indicates about the eclosion of eggs.
  • Observation of a turtle doing the lay.
  • Remainder of eggs or hatching animals.

REFERENCES 

• Consejería de Medio Ambiente de la Junta de Andalucía (2014). Varamientos de Especies Marinas Amenazadas. Guías prácticas voluntariado ambiental.
• Gray, J (1997). Marine biodiversity: patterns, threats and conservation needs. Biodiversity and Conservation 6, 153-175
• Hamann, M et al. ‘Climate Change And Marine Turtles’. The Biology Of Sea Turtles. Volume III. Jeanette Wyneken, Kenneth J. Lohmann and John A. Musick. 1st ed. New York: CRC Press, 2013. 353-378. Print.
• Harrould-Kolieb, E. & Savitz, J. (2009). Acidificación: ¿Cómo afecta el CO2 a los océanos? Oceana
• Ministerio de Agricultura, Alimentación y Medio Ambiente. Guía de buenas prácticas en las Zonas Especiales de Conservación de ámbito marino de Canarias. España. http://www.magrama.gob.es/es/costas/temas/proteccion-medio-marino/201311_guia_bbpp_web_tcm7-229984.pdf
• Oceana (2006). Las tortugas marinas en el Mediterráneo. Amenazas y soluciones para la supervivencia. 38 pp.
• Otero, M., Garrabou, J., Vargas, M. 2013. Mediterranean Marine Protected Areas and climate change: A guide to regional monitoring and adaptation opportunities. Malaga, Spain: IUCN. 52 pages.
• Shigenaka, G (2010). Oil and Sea Turtles. Biology, planning and response. NOAA
• Smith, T & Smith R (2007). Ecología. Pearson Educación (6 ed.)
• Velegrakis, A., Hasiotis, T., Monioudi, I., Manoutsoglou, E., Psarros, F., Andreadis, O. and Tziourrou, P., (2013). Evaluation of climate change impacts on the sea-turtle nesting beaches of the National Marine Park of Zakynthos Protected Area. Med-PAN North Project, Final report, 81 pp.

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.

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.

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.

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.

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 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.)