The World’s First Global Glimpse of Leatherback Nesting Beaches
A leatherback nest is excavated after the hatchlings have emerged to assess the success rate of the nest. © JOHAN GODFREY
By Roderic B. Mast
Every night, come rain or a shining moon, hundreds of field biologists, conservationists, and volunteers around the world don their flashlights and head to the beach, pacing the shoreline all night long to document the lives of sea turtles and to protect their nests and nesting habitats. Separated by thousands of miles and often living in remote areas, speaking different languages and facing unique challenges, the people involved in these projects are worlds away from one another. Yet all share a common vision: a world with healthy oceans and coasts in which sea turtles continue to live and to thrive. And now they have come together in the State of the World’s Sea Turtles (SWoT) initiative, calling themselves the “SWoT Team,” and taking a collective step forward to make that vision a reality.
Over the past two years, researchers around the world have contributed their time, energy, and scientific data to SWoT, in an effort to map the leatherback nesting beaches of the world with the best available information from the last complete nesting season in 2004— results of which are displayed on the maps on pages 18–19, and in the citations at the end of this publication.
Our modern age is one of information and technology in which traditional barriers to information access have all but disappeared. Hundreds of satellites orbit the earth, relaying and collecting information. A researcher on the Amazon River sends emails to colleagues in Tokyo on a handheld cellular phone. Remote rovers explore the surface of Mars and instantly send data back home. Nevertheless, the biological data necessary for effective conservation planning often remain scattered and inaccessible. Slowly, this is changing.
Leatherback hatchlings head to sea. © SUZANNE LIVINGSTONE / UNIVERSITY OF GLASGOW
In the case of sea turtles, a plethora of useful data exist at the local, national, and in some cases regional level; yet previously there have been no up-to-date global-scale presentations of these data. This has been an enormous disadvantage for conservation planners, government bodies, and the sea turtle conservation movement itself, as we attempt to seek direction for our actions in the context of the big picture. On a global level, there is an urgent need to know the status of all sea turtles—all populations and all life stages—so that we can effectively prioritize our actions.
The truth is that no matter what we do, we cannot protect every sea turtle, every nesting beach, every foraging ground, or every migratory pathway. So as we seek to prevent extinctions, where do we invest our time and money for greatest impact?
Global data such as that presented by SWoT in the first worldwide mapping of leatherback sea turtle nesting data on pages 18–19 of SWOT Report, vol. 1 (2006), will help us to set our global priorities and to answer that question thoroughly and thoughtfully.
The Challenge of Collective Conservation: An Insight into Gathering Global Data
By Brian J. Hutchinson and María Fernanda Pérez
Sea turtles are global creatures, and the leatherback especially so, as its nesting distribution circles the globe (see map at bottom). And when they are not reproducing, leatherbacks swim thousands of miles and cross entire ocean basins. One of the greatest challenges we face in conserving leatherbacks is seeing the big picture and taking local actions that can have global significance in preventing extinction.
The SWoT Team has committed to this challenge by bettering this big picture, our global view of leatherbacks. Our first step has been to compile information on leatherback nesting. Over the past two years, the SWoT Team has documented 203 leatherback nesting sites in 46 countries. Nesting data from the last complete nesting season in 2004 were contributed from 89 of these sites, and the remaining 114 either did not participate or do not have beach monitoring programs.
Effectively creating this global picture has required carefully dealing with critical data deficiencies and incompatibilities. First, there are likely many leatherback nesting sites that have not been discovered, and even among the sites that we know exist, many have incomplete or no data on their turtles. Moreover, there is a good deal of incompatibility among data sets. With information from nearly 100 sources and so many different areas of the world, we are faced with the tremendous challenge of creating uniformity among these diverse data sets. For example, some beach projects count the number of females, or the number of nests per season, while others count the number of crawls per season. Perhaps even more complicated, data are collected under a wide range of monitoring efforts. Some projects monitor 100 percent of the nesting beach during the nesting season or even all year, whereas other projects may have no regular beach monitoring; data might be collected only three mornings a week on only a portion of the beach, or during a one-day aerial survey along the coastline of an entire country. The result is that one beach may appear to have more nesting turtles than another, when in reality this is due to differences in monitoring effort.
Measures of monitoring effort are typically not well documented, and as such we are unable to evaluate the relative monitoring effort at each beach. Thus we cannot extrapolate full-season nesting values at beaches with partial coverage. Therefore, caution must be exercised when comparing the relative nesting between sites displayed in the SWoT map.
Although we have made every attempt to address these issues and present the most accurate picture possible, some notable assumptions were required in presenting these data. For the central map (pp. 18–19) we show the number of leatherback females nesting annually at all possible beaches. Because the number of nesting females is not available from every beach, for certain beaches we have estimated by dividing the recorded number of nests by a conversion value. It is important to note, therefore, that many of the points on the map are based on estimates and not actual numbers.
We have separated nesting populations into two categories: those with their main foraging grounds in the Northern Hemisphere, and those with their main foraging grounds in the Southern Hemisphere. For each of these categories, we have selected a single clutch frequency value (average nests per female per year) to estimate the number of females nesting annually for rookeries within that category. These average clutch frequencies are taken from the best-studied nesting rookeries in each group. For the Northern Hemisphere foragers, this rookery is at Sandy Point, St. Croix, U.S. Virgin Islands, and the average number of nests laid per female in 2004 was 4.64—the observed clutch frequency (Alexander et al. 2004). For the Southern Hemisphere foragers, it is Playa Grande, Costa Rica, where the estimated clutch frequency in 2003–2004 was 7.24 (Paladino & Spotila, pers. comm.).
This map and database is an initial step in a long and evolving process. Recognizing the limitations and imperfections of this first step, we are committed to improving and refining this work over time. As we move into the future, the SWoT network will continue to grow, and we will update the SWoT database and find new ways to use these data for conservation action and to improve our understanding of the status of the world’s sea turtles.
Worldwide Leatherback Nesting Sites 2004 (data citations) | SWOT Report, vol. I (2006).
This article originally appeared in SWOT Report, vol. 1 (2006). Click here to download the entire article as a PDF.