Stan Ulanski: Wanderers of the Pacific Ocean: Sea Turtles

We welcome to the blog a guest post by Stan Ulanski, author of The California Current: A Pacific Ecosystem and Its Fliers, Divers, and Swimmers. The California Current—part of the large, swirling North Pacific gyre—flows slowly southward along the west coast of North America, stretching nearly 2,000 miles from southern British Columbia to the tip of Baja California in Mexico. To a casual observer standing on the shore, the vast current betrays no discernible signs, yet life abounds just over the horizon. Ulanski takes us into the water on a journey through this magnificent, unique marine ecosystem, illuminating the scientific and biological marvels and the astonishing array of flora and fauna streaming along our Pacific coast.

In today’s post, Ulanski shares a glimpse into the world of living dinosaurs of the sea: Pacific sea turtles. 

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As I researched and studied the myriad organisms that swim in and fly over the California Current for my book on this unique ecosystem, none caught my attention more than Pacific sea turtles—living dinosaurs of the ocean. Theirs is an old story—one of long journeys and nesting rituals performed over the eons. The tale below chronicles the journey and trials of a determined sea turtle.

Travelling thousands of miles from her home waters in the California Current, a massive leatherback turtle weighing upwards of 400 pounds lumbers up a remote beach in the Indonesian archipelago. She is laser focused on only one goal: to lay her eggs in the soft beach sands—a ritual that has been played out over the ages by her ancestors. The probability is high that the beach she has chosen is the same one from which she was hatched more than thirty years ago.

Under the cover of darkness, she finds a suitable nesting site above the high tide line and diligently excavates a hole big enough to hold the dozens of eggs she will deposit. With the eggs carefully set in place, she begins the time-consuming task of covering them up, using her big flippers like paddles to shovel sand into the nest cavity. Satisfied that her nest is secure from predators, she returns to the sea, but only briefly. In ten days, she will return to the beach to deposit another clutch of eggs, a chore she may repeat as many as eleven times during the nesting season. But soon her instincts tell her it is time to leave and begin a long journey thousands of miles across the Pacific. Though a powerful, deliberate swimmer, she will take months to complete her arduous migration. She will most likely ride the great subtropical North Pacific gyre—a complex of ocean currents—to the California coast.

But her journey will not be without peril. She must survive a gauntlet of obstacles, primarily from commercial fisheries. She particularly runs the risk of being caught in longlines, thousands of baited hooks hanging from a thick monofilament mainline that stretches tens of miles behind the boat. Global estimates of the impacts on leatherbacks of longlining operations on the high seas are staggering—thousands are injured or killed each year. If our intrepid wanderer that has migrated across the Pacific has had the good fortune to avoid being captured by longlines, another danger looms: gill nets—large, rectangular nets that ensnare a host of marine organisms. Stretching more than a mile in length and covering over 1 million square feet—the equivalent of twenty-one football fields—gill nets have become known as invisible “curtains of death.”

Our nomadic turtle is one of five sea turtle species, including loggerheads, greens, hawksbills, and olive ridleys, which can be found within the California Current. Sea turtles have been swimming the world’s oceans for tens of millions of years, but recent genetic analysis suggests that leatherbacks may be the most ancient, dating back some 60 to 100 million years ago.

How sea turtles navigate in a vast, featureless ocean has come to light in recent years. Researchers at the University of North Carolina in Chapel Hill have shown that sea turtles have an internal compass for maintaining their direction that depends on their ability to detect subtle differences in the earth’s magnetic field intensity and inclination.

To many sea turtle biologists, the answer to sea turtle migration lies in ancient programming. A particular nesting choice reflects centuries-old conditions that made some sites preferable to sea turtles. Does the beach have the right slope so that the hatchlings can make their way to the sea? What predators, if any, lurk nearby? In the world of sea turtle real estate, the axiom “location, location, location” takes on a life-and-death meaning. In the end, turtle real estate decisions come down to historical experience acquired over long periods and passed down from generation to generation. The rationale is simple: a beach that worked for a mother turtle when she was a hatchling will work for her offspring.

Stan Ulanski, professor of geology and environmental science at James Madison University, is author of The California Current: A Pacific Ecosystem and Its Fliers, Divers, and Swimmers; The Gulf Stream: Tiny Plankton, Giant Bluefin, and the Amazing Story of the Powerful River in the Atlantic; and Fishing North Carolina’s Outer Banks: The Complete Guide to Catching More Fish from Surf, Pier, Sound, and Ocean. For more posts by Ulanski on the blog, see “A Floating Jungle: The Sargassum Community” and “Catch of the Day: Spanish Mackerel.”