Seven Sea Turtle Wonders

Artwork by Mike Yap

To develop an appreciation for something can take as little as a glimpse – an instant connection – or sometimes a profound amount of time to see the beauty within. In the life of James Spotila, a remarkable sea turtle biologist, it only took a sighting of a healthy leatherback about to lay its eggs to be held captivated by it forever. Such a moment held a big part of him, enough to commit his lifetime into studying these wonderful, often miraculous sea creatures.

Since World Sea Turtle Day, June 16, is especially dedicated to the 7 sea turtle species (Green turtle, Leatherback, Kemp’s Ridley, Olive Ridley, Hawksbill, Loggerhead and Flatback) we have today, let us take the time to see how amazing and resilient they really are.

1. Did you know that sea turtles don’t have sex chromosomes? Instead, sex is determined by temperature at which eggs incubate. In the case of green turtles, at 28^oC, hatchlings develop into males; at 31^oC the hatchlings grow into females [1]. This has great implication in conservation [2].

2. The largest recorded leatherback turtle weighs nearly a ton [1]. With jellyfish as its main food, it’s kind of hard to imagine how much it has to eat to weigh that much.

3. Sea turtles have magnetite in their brains; they use it as their internal magnetic compass [1]. They don’t have the superpowers of Magneto but they are tuned to migrate thousands of miles in the ocean and get back to the beach were they hatched.

4. Different species bury their eggs in sand at varying depths. Don't worry the eggs have porous shells so they can breathe. The shallowest depth is observed for Olive ridley and Kemp’s rildey nests at 15 inches while the deepest is for leatherback eggs buried at 25 inches. The deeper it is, the more stable the temperature [2].

5. Sea turtles have to spend at least a decade or more in the open sea before going to back to mate and reproduce in their natal beach [1]. Imagine that they are already independent from the time that they were hatchlings, racing to the open sea. It only becomes tougher (and tougher) for the succeeding years as they have to avoid being captured in destructive shrimp trawls, longlines, and gillnets. What is more worrisome is their affinity to ingest plastics which they mistake for a sumptuous jellyfish.

6. Sea turtles are excellent divers and can prolong their breathing underwater for 45 minutes. The deepest dive a leatherback has bagged is 4250 m [3], beating that of a sperm whale at 3686 m [1].

7. They have survived the mass extinction which obliterated dinosaurs and so have lived for 110 million years now [1]. And it is of course in our hands to make certain that they get to be seen and conserved by the next generations.

The list of how beautiful sea turtles are goes on. Never cease to see and celebrate what’s amazing.

We have considerable information on the seven species of sea turtles. Feel free to visit us at SeaLifeBase, or become a collaborator. Happy World Sea Turtle Day!

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[1] Spotila, J.R. (2004). Sea Turtles: A Complete Guide to their Biology, Behavior and Conservation. The Johns Hopkins University Press.

[2] Spotila, J.R. (2011). Saving Sea Turtles. The Johns Hopkins University Press.

[3] OBIS Search Interface. http://www.iobis.org/mapper/ [Accessed 6/8/2015]. 

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A Sea Turtle's Magnetic Voyage Back Home

Photo from www.arkive.org

Once they reach adulthood, sea turtles (e.g. Caretta caretta^[1]), along with salmon and other marine mammals, travel thousands of miles across the open ocean only to return home to reproduce at the very coastal line where they hatched [2,3,4]. This amazing feat has baffled scientists for fifty years now [2].

Then how come they know their way home? New evidence points out that they “imprint” on magnetic fields as hatchlings and use these magnetic features as signature cues to return to their natal beach as adults [2,3]. Since early studies proved difficult in studying them in the open ocean, scientists took advantage of looking into changes in their behavior in response to changes in magnetic fields instead [2].

By processing a long-standing database, scientists found a strong link between the subtle shifts in the Earth’s magnetic field and the spatial distribution of the turtle nests. Only to confirm their theory: slight shifts in the Earth’s field resulted to coming together of adjacent magnetic signatures, hence gathering sea turtles in a much shorter coastline. Consequently, diverging magnetic signatures meant sparse eggs were laid and nests were farther from each other. This new evidence indicates that changes in magnetic fields influence where turtles will nest [2].

To learn more about sea turtles visit SeaLifeBase and to read more on salmons, visit FishBase.

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[1] SeaLifeBase. Caretta caretta (Linnaeus, 1758). Retrieved January 27, 2015 from http://sealifebase.ca/summary/Caretta-caretta.html#.

[2] Cell Press. (2015, January 15). For sea turtles, there’s no place like magnetic home. ScienceDaily. Retrieved January 18, 2015 from www.sciencedaily.com/releases/2015/01/150115134713.htm

[3] Lohmann, K.J., Putman, N.F., Lohmann, C.M. (2008). Geomagnetic imprinting: a unifying hypothesis of long-distance natal homing in salmon and sea turtles. Proceedings of the National Academy of Sciences 105(49): 19096-19101.

[4] Putman, N.F., Lohmann, K.J., Putman, E.M., Quinn, T.P., Klimley, A.P., Noakes, D.L.G. (2013). Evidence of geomagnetic imprinting as a homing mechanism in Pacific salmon. Current Biology 23(4):312-316.

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