Seeing the Big Picture: Leatherback Migrations in the Pacific
By Scott R. Benson
In the Pacific Ocean, leatherback turtles routinely make epic journeys of tens of thousands of miles between tropical breeding areas and frigid-water feeding areas. A newly completed, multiyear satellite tracking study provides the best picture yet of the jaw-dropping migratory abilities of these animals.
Leatherbacks that feed in the central North Pacific Ocean and off the West Coast of the United States also nest year-round in several western Pacific Island nations. To connect the leatherback dots across the vast Pacific, a large-scale research program was undertaken to study western Pacific leatherback movements, high-use areas, and habitat associations by tracking leatherbacks with telemetry devices during both their east-west and west-east migrations. This program conducted a massive deployment of more than 100 satellite transmitters over the course of nearly a decade on nesting and feeding leatherbacks; then it used sophisticated statistical modeling to process location data and to interpret movements and behavior patterns for each turtle. When all the data came together, several startling discoveries came into focus.
One of the biggest surprises was the clear separation of migratory destinations by nesting season (see map). Leatherbacks that nested during summer (indicated by the red lines on the map) moved into large marine ecosystems (LMEs) of the temperate North Pacific Ocean, including areas of open ocean in the central Pacific, as well as into coastal areas off the United States, into the tropical waters of the South China Sea, and around Malaysia and the Philippines. Meanwhile, turtles that nested during winter (indicated by the blue lines on the map) moved into temperate and tropical LMEs of the Southern Hemisphere, around southeastern Australia and New Zealand, and into tropical Indonesian seas. Foraging behaviors (indicated by the colored dots on the map) occurred in temperate and tropical waters and in numerous pelagic and coastal regions that showed a wide range of oceanographic features known to aggregate leatherbacks’ favorite prey—jellies.
For turtles to access the most distant foraging ground—the California Current LME—required a 10- to 12-month trans-Pacific migration of up to 11,400 kilometers (7,000 miles) and commonly involved multiple years of migrating between high-latitude summer foraging grounds and low-latitude eastern tropical Pacific wintering areas without returning to their western Pacific nesting beaches (green lines show turtles tracked from feeding areas in the United States). In contrast, tropical foraging destinations were reached within 5 to 7 months and appeared to support year-round foraging. This difference between time—and energy—spent during these two migratory strategies (to distant temperate foraging areas and to closer tropical foraging areas) could result in differences in biological traits such as body size and reproductive output among nesting females of this western Pacific population.
What do these statistics mean for conservation? The variation in movements and foraging strategies that leatherbacks show actually underscores the importance of ocean wide and ecosystem-based management (see “Turtles Need a Pacific Oceanscape as Much as People Do,” this issue). As their Pacific peregrinations show, leatherbacks are indifferent to time zones, national borders, and other geopolitical boundaries, making them effective maritime ambassadors for conservation partnerships throughout the Pacific. We should follow their lead and create conservation strategies that reflect their wide ranging, boundary-crossing ways.
This article originally appeared in SWOT Report, vol. 7 (2012). Click here to download the entire article as a PDF.