The Mystery of Lost Little Turtles: Where do sea turtles spend their first years of life
In August 2006, a handful of international sea turtle experts gathered in Washington, D.C., to address critical issues in sea turtle conservation at the third Burning Issues retreat of the IUCN– World Conservation Union’s Marine Turtle Specialist Group, a meeting now referred to as BI:3. Much like the film MI:3, the BI:3 team tackled the “Mission Impossible” of defining the great unanswered questions, armed with only a few centuries of cumulative firsthand experience and the results of a simple survey administered among some 300 of the world’s leading sea turtle experts from 80 countries.
Framing the questions is a first step in creating plans and strategies that will eventually fill critical knowledge gaps and lead to sound conservation strategies. The results of BI:3—the seven unsolved mysteries described in these next articles—highlight the great unknowns about sea turtles. They provide a framework for focusing scientific progress, intellectual powers, and investment in global research, and they serve as a public relations tool to generate greater interest and financing for conserving marine turtles and their habitats.
The following questions are the result of BI:3, the third Burning Issues retreat of the IUCN Species Survival Commission’s Marine Turtle Specialist Group, Washington, D.C., August 2006. They are addressed in the following articles, written by sea turtle experts from around the world.
The Mystery of Lost Little Turtles: Where do sea turtles spend their first years of life?
Hawksbill hatchlings emerge from the nest and make their way toward the sea. © NICOLAS J. PILCHER
By Blair Witherington
On entering the world, sea turtles almost immediately get lost. These tiny, finger-length hatchlings scramble from their sandy nests, rush into the surf, and beat their flippers out to sea beyond where scientists can comfortably catalog their lives.
It is not that the turtles themselves are lost. To the contrary, even little turtles in a big ocean seem to know a lot about where they are and where they would like to be. “Elusive” is a better word to describe these youngsters. They are certainly lost to us, as terrestrial observers, until they reappear as juveniles swimming in coastal waters where we can more easily locate them. Most important for the turtles, life upon the open ocean means that they are lost to the wide variety of coastal predators that would make them a meal during this initial, bite-sized life stage. Indeed, disappearing into a big ocean is reasoned to be an important survival strategy for young sea turtles.
Hatchlings of all sea turtle species disperse as they swim away from the nesting beach. This scattering begins with the hatchling frenzy—a burst of swimming that propels them away from the shore, where predatory fish concentrate and where currents could sweep them back onto land. For all species but the flatback, this initial burn of swim energy often boosts hatchlings into currents that orbit entire ocean basins. For these hatchlings, a few days of directed swimming launches a drifting journey that may span many years and thousands of miles. Life is distributed in patches in the open ocean—a great benefit to a tiny drifter wishing to avoid predatory encounters. To live and to grow, however, a turtle must find food in this vast liquid desert. There are occasional concentrations of food at the surface, but these oceanic oases are fleeting. Such phenomena occur at the whim of shear zones between ocean currents, eddy centers, downwellings where currents collide, and upwellings where deep water meets the surface. These are oceanographic events that assemble floating life, such as plankton, seaweed, creatures that cling to flotsam, and young turtles. The menu at these sea turtle smorgasbords includes tiny crustaceans, jelly plankton, sailing snails, blue-button chondrophores, and a wide variety of small, slow-moving creatures such as barnacles, hydroids, bryozoans, and tubeworms.
To avoid being part of the menu themselves, little turtles have ways of avoiding attention. Young loggerheads, hawksbills, and Ridleys try to blend in with the flotsam. When small, these turtles are lumpy and grayish or brownish, much like the other floating matter at the surface. Most young turtles seen on the open ocean remain close to other floating items and are almost as inactive as their surroundings, frequently floating in a “tuck” position, with their flippers held tightly against their body. Small green turtles and leatherbacks are a bit more active, relying on countershading to hide them from predators both above and below. This is most evident in young oceanic green turtles, which are bright white underneath (like the bright sky seen from below) and deep charcoal blue on top (like the dark ocean depths as seen from above).
There are many other mysteries about the lives of these smallest sea turtles. How quickly do they grow? How long is their oceanic stage? Which food items are most important? How do they conserve energy between meals? Do they depend on currents to bring meals, or do they actively seek their food? Are we able to pinpoint the areas of ocean where young sea turtles concentrate? What proportion of turtles survives the oceanic stage? How many succumb to effects from ingesting ubiquitous plastics and tar? Are oil spills and other floating hazards that concentrate with turtles critical threats to their populations?
The clues will not come easily. Sea turtles, it seems, are animals for which mystery is an adaptation. Getting lost and remaining elusive is to be expected, especially for the segment of their lives lived in the wildest and most remote portions of our planet.
This article originally appeared in SWOT Report, vol. 2 (2007). Click here to download the entire article as a PDF.