Satellite tracking provides clues to the ‘lost years’ of South Atlantic sea turtles

South Atlantic sea turtles do not passively ride dominant currents as is historically assumed, but actively swim and orient themselves to stay offshore. Depending on whether they hatch early, in the middle or at the end of the hatching season of sea turtles, they travel in different and sometimes opposite directions, including in the northern hemisphere. Credit: Projeto TAMAR

University of Central Florida biologist whose groundbreaking work tracking the movements of year-old sea turtles in the North Atlantic Ocean has gained international attention has completed a similar study in the South Atlantic with results surprising.

South Atlantic sea turtles do not passively ride dominant currents as is historically assumed, but actively swim and orient themselves to stay offshore. Depending on whether they hatch early, in the middle or at the end of the hatching season of sea turtles, they travel in different and sometimes opposite directions, including in the northern hemisphere.

“From a conservation perspective, it’s important to understand where the youngest sea turtles go and how they interact with their environment,” said assistant biology professor Kate Mansfield who led the study. “Knowing that they are dispersing in different directions, based on changes in ocean currents, will help us better understand where and when we need conservation efforts to ensure the continued survival of these protected species.”

The team’s findings are published today in the Proceedings of the Royal Society B.

This study was a collaboration between UCF, the Brazilian marine turtle conservation group Projeto TAMAR and the National Oceanic and Atmospheric Administration Fisheries. Studying turtles in the South Atlantic provides insight into the “lost years” of sea turtles, the time after they hatch and leave the sea, and before they return closer to shore below. forms large juveniles several years to a decade later. . Very little is known about these young turtles during their early years at sea.

“This study helps fill some long-standing data gaps in our knowledge of the life cycle of marine turtles among Brazilian turtles,” said Milagros Mendilaharsu, co-author with Projeto TAMAR.

Young turtles must survive for several years on the high seas and a few decades in coastal waters before they reach maturity and contribute to their populations, Mansfield said. Sea turtles are very late maturing and long-lived creatures, which makes it difficult to know and understand the “lost years”.

The team followed 19 loggerhead turtles for more than 120 days off the coast of Bahia, Brazil. The turtles in the study were released at the start of the hatching season when the prevailing currents are southerly, in the middle of the hatching season when the currents begin to shift from north to south, and at the end of the hatching season when the offshore currents move mainly north. /North West.

Passive floats, or oceanographic dinghies, were released with the satellite tagged turtles to test their swimming behavior. The floats also served as a comparison between the behavior of turtles and known passive drifting objects that would move with the currents.

The team found that at the start of the hatching season, the majority of the turtles followed the strong currents to the south. Turtles released in the middle of the season first moved south and three eventually veered north as the currents shifted. All of the drifting buoys accompanying these turtles ran aground within a month, but all of the turtles stayed offshore.

At the end of the hatching season, when the currents moved north and west, the turtles moved evenly north and northwest across the equator. Mansfield said active orientation combined with swimming behavior helps turtles stay off the Brazilian continental shelf instead of being led down to land like wanderers.

“Biologically speaking, it’s fascinating,” Mansfield said.

Mansfield’s 2014 study, which looked at loggerhead turtles in the North Atlantic, provided some of the first glimpses of those “lost years”. In this study, many tracked turtles unexpectedly left the currents associated with the North Atlantic Subtropical Gyre, a large circular current system in the North Atlantic Ocean, and entered the Sargasso Sea, an area with inside the gyre. A similar vortex, the South Atlantic subtropical vortex, exists in the South Atlantic, but southern sea turtles have not acted in the same way.

Another co-author, Nathan Putman, senior scientist at LGL Research, said the observed movement patterns can be “like money invested in a diverse range of stocks. This can allow Brazilian turtles to spread the risk for their offspring between two largely independent oceans. basins, fostering a resilient population. In fact, this appears to be the case for the loggerheads of Brazil. “

Unlike other populations that have experienced dramatic declines or increases, these appear to be fairly stable – much like money invested in a diverse range of stocks, ”Putman said.

Mansfield said: “As we track more young turtles in different ocean basins under different oceanographic conditions, we find that long-held assumptions and assumptions about the behavior of ‘lost year’ sea turtles are too limited – an assumption can’t explain everything. “

With improved technology and miniaturization of satellite beacons – such as the beacons developed by the ICARUS Initiative that Mansfield intends to deploy as part of the next steps in his research: https://icarusinitiative.org/ – the researchers said it would be exciting to learn more about these young sailors.


Myth of the broken ocean: “toddler” sea turtles are very active swimmers


More information:
First satellite traces of the “lost years” of sea turtles in the South Atlantic: seasonal variation of the transequatorial movement, Proceedings of the Royal Society B, rspb.royalsocietypublishing.or… .1098 / rspb.2017.1730

Provided by the University of Central Florida


Quote: Satellite tracking provides clues to the “lost years” of South Atlantic sea turtles (December 6, 2017, retrieved October 5, 2021 from https://phys.org/news/2017-12-satellite- tracking-clues-south-atlantic. html

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