Tags slow down young turtles

To learn more about marine life, scientists often attach instrumented tags to animals and record data on their environment and behavior. But these tags could drag down the movements of young turtles, making it harder for the animals to complete long journeys across the ocean.

This isn’t the first time that researchers have reported the ill effects of tags. In one study, a team found that birds fitted with tags have to expend more energy. Even when the instruments were less than 1% of their weight, tagged penguins took longer to find food and had less fat.

The researchers searched scientific papers published from 2000 to 2012 and found that tagging of marine turtles was mentioned in about 50 papers per year. Since young turtles have to migrate long distances, “long-term attachment of instruments with high drag costs may have considerable ecological implications,” the authors write in Methods in Ecology and Evolution.

To quantify the effects on drag, the team created fiberglass casts of several types of marine turtles, including leatherback, green, and hawksbill turtles. The researchers attached tags to the casts and placed them in a wind tunnel. They could then estimate the change in drag that the animal might experience while swimming.

For adult-sized turtles, tags generally increased drag by less than 5 percent. But for juvenile turtles, drag jumped by more than 100 percent. “If the drag costs from carrying tags disrupts their natural behaviour, they may miss out on breeding and foraging seasons, be unable to catch enough food, or even end up becoming someone else’s meal,” said study co-author T. Todd Jones of the National Oceanic and Atmospheric Administration Pacific Islands Fisheries Science Center in Honolulu, Hawaii in a press release.

There is one thing that scientists can do to help the animals out: Turtles are often encrusted with barnacles that also increase drag. So cleaning off the barnacles “may offset the increased drag from instrumentation,” the authors note. Roberta Kwok | 8 November 2013

Source: Jones, T.T. et al. 2013. Calculating the ecological impacts of animal-borne instruments on aquatic organisms. Methods in Ecology and Evolution doi: 10.1111/2041-210X.12109.

Image © Fifian Iromi | Shutterstock

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