FOR IMMEDIATE RELEASE May 24, 2021
Release #2129 Point of Contact—Jeffrey Prater (401) 832-2039
NUWC Division Newport team develops new model for estimating abundance of loggerhead turtles in the Mediterranean
A Naval Undersea Warfare Center Division Newport scientist and support contractor have a new model for estimating loggerhead sea turtle abundance.
Since early 2019, Environmental Branch employees Laura Sparks, a resident of Foster, Rhode Island, and Andrew DiMatteo, a support contractor and a resident of Berthoud, Colorado, have worked to measure the density, abundance and distribution of loggerhead turtles — a globally vulnerable species — in the Mediterranean Sea. The model, which was adopted from a similar process used with other marine mammal species, was finalized in mid-2020.
“Our model accounts for juvenile and adult loggerheads in the Mediterranean Sea regardless of their population of origin,” Sparks said. “This provides the first estimate of population abundance unrelated to demographic estimates, which are usually derived from data on nesting beaches.”
This model allows for managers to prioritize marine protected areas, conservation interventions and research priorities for loggerheads on a basin-wide scale for the first time. Sparks and DiMatteo estimate there are roughly 994,000 loggerheads in the Mediterranean. This knowledge will help the Navy assess and potentially mitigate impacts on loggerhead turtles from naval training and testing exercises.
“Loggerhead turtles face many threats in the Mediterranean, such as capture in fisheries, shoreline development, vessel traffic and climate change,” DiMatteo said. “While this specific population is listed as a least concern by the International Union for Conservation of Nature, the species is globally listed as threatened and still depends on conservationists to survive in this region.”
Previous density estimates in the region were limited by individual surveys covering smaller areas, and the only total population estimates came from monitoring the beaches where the turtles nest. A combination of methods, Sparks said, were used to develop this tool.
“Here, NUWC uses aerial and shipboard line transect data collected between 2003 and 2018 from multiple surveys to estimate density and abundance throughout the Mediterranean Sea using distance sampling methodology,” Sparks said. “A spatial density model estimating loggerhead density, abundance and distribution across the Mediterranean Sea was generated as a long-term annual average across the study period.
“The model was adjusted for how much time loggerhead turtles spend diving by collecting data from animals tagged with time depth recorders from multiple regions within the Mediterranean Sea.”
While a novel approach in loggerhead turtle research, Sparks and DiMatteo admit there are some limitations to consider. While trained marine species observers are tremendously talented, sighting animals can be complicated by conditions, such as sun or large waves.
“Most marine species dive and are deep underwater part of the time, further complicating accurate detection of animals,” DiMatteo said. “This needs to be accounted for in the analysis afterwards.”
Another flaw is that it is difficult to detect animals smaller than 30cm — a large proportion of the population — with this method. Thus, the researchers note, that it is important to consider their method with previously established ones in unison, rather than separately.
“Having two independent estimates of population gives us a better sense that we are correct if estimates are similar,” DiMatteo said. “If they are wildly different, we can go back to both models, question our assumptions and look for errors to see why they are so different.
“Happily, our survey-based estimate was statistically similar to the previous demographic estimate. This means we have more confidence that both are probably in the right ballpark.”
This project supports a larger density data collection effort known as the Navy Marine Species Density Database (NMSDD). The NMSDD compiles density data in different training and testing areas, including the Mediterranean Sea.
“Previous work funded by the Navy developed a set of marine mammal density models for the Mediterranean Sea using the same surveys we used, but that group did not have the expertise or funding to develop sea turtle models,” Sparks said. “We saw an opportunity to fill a data gap both for the Navy and for the sea turtle conservation community in the Mediterranean Sea by leveraging this existing collaboration.”
This project would not have been possible, Sparks said, without the help of a number of other naval commands, conservation organizations and universities.
The next step for the researchers will be to produce similar density surface models for several species of sea turtles along the east coast of the U.S. They also are hoping to present their findings to the scientific community at a conference, which was delayed because of the COVID-19 pandemic.
The Division Newport scientists worked in collaboration with the following data providers: Blue World Institute, the University of Valencia, Tethys Institute, ISPRA, IFAW, the University of Exeter, ACCOBAMS, PELAGIS, Alnitak, Stazione Zoologica, Anton Dorne, Julie Belmont, Simone Panigada, Olivier Boisseau, Giancarlo Lauriano, Drasko Holcer, Caterina Fortuna, Vincent Ridoux, Helene Peltier, Toni Raga, David March, Robin Snape, Sandra Hochscheid, Annette Broderick, Brendan Godley, Robin Snape and Julia Haywood.
Technical support for the project was given by Jason Roberts and Ana Canadas from Duke University, Elizabeth Becker From ManTech Inc., and David Miller from the University of St. Andrews. Danielle Jones of Naval Facilities Engineering Command Atlantic assisted with project management and funding was provided by U.S. Fleet Forces Command.
The full report is available at: https://apps.dtic.mil/sti/pdfs/AD1120818.pdf
NUWC Division Newport is a shore command of the U.S. Navy within the Naval Sea Systems Command, which engineers, builds and supports America’s fleet of ships and combat systems. NUWC Newport provides research, development, test and evaluation, engineering and fleet support for submarines, autonomous underwater systems, undersea offensive and defensive weapons systems, and countermeasures associated with undersea warfare.
NUWC Newport is the oldest warfare center in the country, tracing its heritage to the Naval Torpedo Station established on Goat Island in Newport Harbor in 1869. Commanded by Capt. Chad Hennings, NUWC Newport maintains major detachments in West Palm Beach, Florida, and Andros Island in the Bahamas, as well as test facilities at Seneca Lake and Fisher's Island, New York, Leesburg, Florida, and Dodge Pond, Connecticut.