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A Look Into the Mysterious Life of Juvenile Sea Turtles

turtle blog

Credit: Jim Abernethy

Small satellite-tracking devices attached to sea turtles swimming off Florida’s coast have delivered first-of-its-kind data that could help unlock they mystery of what endangered turtles do during the “lost years.”

The “lost years” refers to the time after turtles hatch and head to sea where they remain for many years before returning to near-shore waters as large juveniles. The time period is often referred to as the “lost years” because not much has been known about where the young turtles go and how they interact with their oceanic environment — until now.

“What is exciting is that we provide the first look at the early behavior and movements of young sea turtles in the wild,” said UCF biologist Kate Mansfield, who led the team. “Before this study, most of the scientific information about the early life history of sea turtles was inferred through genetics studies, opportunistic sightings offshore, or laboratory-based studies. With real observations of turtles in their natural environment, we are able to examine and reevaluate existing hypotheses about the turtles’ early life history. This knowledge may help managers provide better protection for these threatened and endangered species.”

Findings from the study appear today in the journal Proceedings of the Royal Society B.

A team of scientists from the UCF, Florida Atlantic University, University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, and University of Wisconsin, tracked 17 loggerhead turtles for 27 to 220 days in the open ocean using small, solar-powered satellite tags. The goal was to better understand the turtles’ movements, habitat preferences, and what role temperature may play in early sea turtle life history.

Some of the findings challenge previously held beliefs.

While the turtles remain in oceanic waters (traveling between 124 miles to 2,672 miles) off the continental shelf and the loggerhead turtles sought the surface of the water as predicted, the study found that the turtles do not necessarily remain within the currents associated with the North Atlantic subtropical gyre. It was historically thought that loggerhead turtles hatching from Florida’s east coast complete a long, developmental migration in a large circle around the Atlantic entrained in these currents. But the team’s data suggest that turtles may drop out of these currents into the middle of the Atlantic or the Sargasso Sea.

The team also found that while the turtles mostly stayed at the sea surface, where they were exposed to the sun’s energy, the turtles’ shells registered more heat than anticipated (as recorded by sensors in the satellite tags), leading the team to consider a new hypothesis about why the turtles seek refuge in Sargassum. It is a type of seaweed found on the surface of the water in the deep ocean long associated with young sea turtles.

“We propose that young turtles remain at the sea surface to gain a thermal benefit,” Mansfield said. “This makes sense because the turtles are cold blooded animals. By remaining at the sea surface, and by associating with Sargassum habitat, turtles gain a thermal refuge of sorts that may help enhance growth and feeding rates, among other physiological benefits.”

More research will be needed, but it’s a start at cracking the “lost years” mystery.

The findings are important because the loggerhead turtles along with other sea turtles are threatened or endangered species. Florida beaches are important to their survival because they provide important nesting grounds in North America. More than 80% of Atlantic loggerheads nest along Florida’s coast. There are other important nesting grounds and nursing areas for sea turtles in the western hemisphere found from as far north as Virginia to South America and the Caribbean.

“From the time they leave our shores, we don’t hear anything about them until they surface near the Canary Islands, which is like their primary school years,” said Florida Atlantic University professor Jeannette Wyneken, the study’s co- PI and author. “There’s a whole lot that happens during the Atlantic crossing that we knew nothing about. Our work helps to redefine Atlantic loggerhead nursery grounds and early loggerhead habitat use.”

Mansfield joined UCF in 2013. She has a Ph.D. from the Virginia Institute of Marine Science and a master’s degree from the Rosenstiel School of Marine and Atmospheric Science at the University of Miami. She previously worked at Florida International University, through the Cooperative Institute for Marine and Atmospheric Studies (CIMAS) in association with the National Oceanographic and Atmospheric Administration and the National Marine Fisheries Services. She was a National Academies NRC postdoctoral associate based at NOAA’s Southeast Fisheries Science Center, and remains an affiliate faculty in Florida Atlantic University’s biology department where Wyneken is based.

With colleagues at each institution Mansfield conducted re

search that has helped further the understanding of the sea turtle “lost years” and sea turtle life history as a whole. For example she and Wyneken developed a satellite tagging method using a non-toxic manicure acrylic, old wetsuits, and hair-extension glue to attach satellite tags to small turtles. Tagging small turtles is very difficult by traditional means because of their small size and how fast they grow.

 

Published on http://www.sciencedaily.com/releases/2014/03/140304215610.htm based on materials from Proceedings of the Royal Society B: Biological Sciences (http://rspb.royalsocietypublishing.org/content/281/1781/20133039).

Posted June 2nd, 2015.

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Birds of a Feather Flock (Or in this Case, Fish of a Scale Swim) Together

Credit: Image courtesy of Polytechnic Institute of New York University

Brooklyn, New York— Recent studies from two research teams at the Polytechnic Institute of New York University (NYU-Poly) demonstrate how underwater robots can be used to understand and influence the complex swimming behaviors of schooling fish. The teams, led by Maurizio Porfiri, associate professor of mechanical and aerospace engineering at NYU-Poly, published two separate papers in the journalPLOS ONE.

These studies are the latest in a significant body of research by Porfiri and collaborators utilizing robots, specifically robotic fish, to impact collective animal behavior. In collaboration with doctoral candidate Paul Phamduy and NYU-Poly research scholar Giovanni Polverino, Porfiri designed an experiment to examine the interplay of visual cues and flow cues—changes in the water current as a result of tail-beat frequency—in triggering a live golden shiner fish to either approach or ignore a robotic fish.

They designed and built two robotic fish analogous to live golden shiners in aspect ratio, size, shape, and locomotion pattern. However, one was painted with the natural colors of the golden shiner, the other with a palette not seen in the species. The researchers affixed each robot to the inside of a water tunnel, introduced a live golden shiner fish, and observed its interactions with the robot. While the robot’s position remained static, the researchers experimented with several different tail-beat frequencies.

“When the fish encountered a robot that mimicked both the coloration and mean tail-beat frequency for the species, it was likeliest to spend the most time in the nearest proximity to it,” Porfiri said. “The more closely the robot came to approximating a fellow golden shiner, the likelier the fish was to treat it like one, including swimming at the same depth behind the robot, which yields a hydrodynamic advantage,” he explained.

While flow cues created by tail-beat frequency proved to be a critical trigger for shoaling behavior, coloration proved slightly dominant. “Even at tail-beat frequencies that were less than optimal for the live fish, the shiners were always more drawn to the naturally colored robot,” Porfiri added.

Robot speed and body movement were the main focus of another study, also published in PLOS ONE, in which Porfiri teamed with NYU-Poly postdoctoral fellow Sachit Butail and graduate student Tiziana Bartolini. This time, the subject was the zebrafish, and the robot was a free-swimming unit with the coloration, size, aspect ratio, and fin shape of a fertile female member of the species.

The researchers placed the robot in a shared tank with shoals of live zebrafish, aiming to determine if the fish would perceive the robot as a predator, and whether visual cues from the robot could be used to modulate the fishes’ social behavior and activity. The team used a remote control to drive the robot in a circular swimming pattern, while varying its tail-beat frequency. For comparison purposes, they also exposed the fish to the robot in a fixed position, beating its tail.

Experiments showed that while the zebrafish clearly did not perceive the swimming robot as one of their own—they maintained greater distance from the robot than they did to each other—the robot was still an effective stimulus for modulating their social behavior. When the robot was held still in the tank, the live fish showed high group cohesion, along with a strong polarization—meaning the fish were likely to be close to each other and oriented in the same direction. As the robot’s tail-beat frequency increased, it had a profound impact on the group’s collective behavior, causing a spike in the cohesion and a small but detectable decrease in polarization—the fish largely milled together and even matched their speeds to that of the robot as it reached a certain tail-beat frequency.

“This shows us that the fish are responding to more than one stimulus—it’s not just the flow cues, it’s the combination of visual and flow cues that influence the collective response,” Porfiri said.

Porfiri is a leading researcher in the field of ethorobotics—the study of robot-animal interaction. Studies like these advance multiple areas of science, including the development of an experimental animal model based on lower-order species such as fish, with robots providing a consistent, infinitely reproducible stimulus. The use of robots to influence collective animal behavior is also viewed as a potential means to protect marine wildlife, including birds and fish, in the wake of environmental hazard.

This research was supported by the National Science Foundation and the Mitsui USA Foundation.

Source: Polytechnic Institute of New York

Posted June 2nd, 2015.

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