Loggerhead sea turtle nesting activity driven by recent climate conditions and returning nesting

December 16, 2013

New research indicates that for loggerhead sea turtles in the Northwest Atlantic, the number of returning nesting females in the population and favorable climate conditions in the year or two prior to the nesting year are strongly related to the number of nests produced by these animals in a given year. Also, in what may be good news for loggerheads, nesting increases since 2008 may be a recovery response in this threatened population. The study published December 5 in the journal PLOS ONE.

Vincent Saba, a research fishery biologist at NOAA's Northeast Fisheries Science Center (NEFSC), and his study co-authors used annual nest counts from Florida and a time-series of climate data in turtle-nesting population models. These models were then used to assess observed changes in nest counts and to project future nesting trends in the Northwest Atlantic loggerhead sea turtle population, the largest in the world.

"Our study suggests that the cumulative survival from hatchling to maturity, which may take 30 years, combined with present-day climate effects on mature females, has a greater influence on annual nesting population size than does the exclusive impact of survival during the first year of life as hatchlings," Saba said. "The first year of life represents only 3 percent of the time elapsed through age 31."

The study suggests that protection for older juveniles and sub-adults to ensure they reach maturity and breed multiple times is at least as important as protecting hatchlings. These results have major implications for management strategies aimed at the recovery of Northwest Atlantic loggerheads and the projected recovery rates of this population, which is considered threatened under the U.S. Endangered Species Act.

Sea turtles are long-lived, late maturing species that occur throughout the global oceans. Estimated survival rates for loggerhead sea turtles in the Northwest Atlantic are very low; less than 0.2 percent of turtles born in a given year survive to age 30. Because the reproductive value is highest for sea turtles that have reached or are approaching maturity, management strategies protecting these life stages from human threats are critical. Although data are limited to tagging data from nesting beaches, they suggest loggerheads may be reproductively active for 25 years or more.

Nearly 90 percent of all loggerhead nesting in the Northwest Atlantic occurs in Florida. Nest count data between 1989 and 2012 are derived from 15 index beaches located on the east coast of Florida between Canaveral National Seashore and Boca Raton.

The authors used observed nest counts between 1989 and 2012 to model the importance of first-time nesters (aged 31), to future nesting numbers. To do this, they projected the number of nesting females up to 2020 and 2043 based on the estimated number of hatchlings produced between 1989 and 2012. The decline in the annual nest counts observed between 1998 and 2007 was not projected to occur during 2029-2038. This suggests that annual nesting variability and trends are influenced more by returning nesters, older females, than by first-timers. If first-timers contributed more to nesting variability and trends, a decline in the years 2029-2038 would be expected.

Saba and colleagues found that adult female sea turtles are greatly influenced by environmental conditions--referred to as "climate forcing" -- when it comes to annual reproductive activity. Not all female sea turtles in the population nest each year, a phenomenon attributed by some researchers to climate-driven changes in energy consumption at foraging areas in the year(s) prior to nesting. Limited tagging data from nesting beaches suggest that the reproductive longevity of loggerheads may exceed 25 years.

"This study offers a different perspective than earlier work that suggested most of the annual variability in loggerhead sea turtle nest counts in Florida between 1989 and 2010 could be explained by climate forcing on hatchling survival," said Saba, a member of the NEFSC's Ecosystem Assessment Program. "We reached a much different conclusion. The annual variability and trends in loggerhead nesting numbers in Florida are associated with long-term survival at sea from hatchling to maturity, combined with climate-driven changes in mature female foraging areas within a year or two before nesting."

Saba and colleagues used population models to evaluate the relative influence of climate indices including the Atlantic Multidecadal Oscillation, the North Atlantic Oscillation, and the El Niño Southern Oscillation. They then tested for differences in model fits using annual nest count data to see how the model performed with respect to environmental factors. They also assessed the relative contribution of first-time nesters to projected annual nest counts. Lastly, they created a survival matrix to compare the relative importance of survival in the first year of life relative to the next 30 years before maturity was reached.

With passage of the U.S. Endangered Species Act (ESA) in 1973, protection measures have been implemented for all loggerhead life stages. Since the lowest annual loggerhead nest count data from Florida's index beaches occurred thirty years after the ESA was enacted, the authors suggest that the nesting decline that occurred during 1998-2007 was a lagged response to historical human-induced mortality impacts on juveniles and adults. The subsequent increase in nest counts since 2008 reflects a potential recovery response.

Saba, who has conducted modeling studies on the impacts of climate change on endangered leatherback turtles in the eastern Pacific Ocean, says the Northwest Atlantic loggerhead study offers a new approach in understanding how climate variability affects sea turtle populations. The study should also help management efforts aimed at protecting these populations because it suggests that the protection of large juveniles and adults should be a priority.

NOAA Northeast Fisheries Science Center

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.