Feeding the animals is altering the behaviour and eating habits of the green turtle in the Canary Islands (Spain). This is the conclusion of a study published in the journal Science of the Total Environment, carried out by a team in which Lluís Cardona, from the Faculty of Biology and the Biodiversity Research Institute of the University of Barcelona (IRBio) takes part. The study, with Catalina Monzón (University of Las Palmas de Gran Canaria) as first author, is also signed by experts from ASD Biodiversidad, Oceanografic Foundation, and La Tahonilla and Tafira Wildlife Rescue Centers, in the Canary Islands.

The archipelago of the Canary Islands is the most northern area to find the green turtle (Chelonia mydas) in the western Atlantic. This marine turtle -the biggest species of the family of Cheloniidae and the only herbivorous one- is included in the red list of endangered species according to the International Union for Conservation of Nature (IUCN). Living in the seagrass Cymodocea nodosa, it appears occasionally in the western Mediterranean, while it has a resident population in the eastern area, isolated from Atlantic populations.

Feeding: catching animals' attention with food

Wild animals are an attractive advertisement for tourists -which creates important economic benefits. The irresponsible practice of feeding with artificial food is spreading worldwide and affecting several marine species, including the sand tiger shark (Carcharias taurus) and the whale shark (Rhincodon typus). The authors of this new study warn about feeding being a new threat for the green turtle, a species which has been historically threatened for its consumption, and recently, due accidental fishing, sea transit and marine debris.

High consumption of fat, pollutants and behaviour changes

"Offering food to green turtles to get their attention is a practice which is spreading in the Caribbean and is now common in the Canary Islands," says Lluís Cardona, lecturer from the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB and member of the Research Group on Large Marine Vertebrates of the University of Barcelona. "Supplemental feeding has three consequences," he continues. "First, it slows down the adoption of an herbivorous diet, and it increases levels of triglycerides and other blood markers related to the high consumption of proteins and fat. Secondly, it also increases the levels of certain organic and inorganic pollutants. And last, getting them used to human contact makes them more vulnerable to crash into boats and to get captured by fishing gears with hooks, since turtles are attracted by baits."

In the study, the experts applied a wide experimental protocol which includes genetic, biochemical, toxicological analyses as well as analyses of stable isotopes, and the photo-identification and satellite ranging to monitor the population of turtles.

Changing the attitude to protect a marine turtle which is more and more vulnerable

Promoting measures to control recreational activities and improve supervision are priority actions to improve the conservation of the species, which has sharks as the main predators -also big fish and marine birds for the offspring- and which makes broad migrations from the feeding area to the nesting beaches in tropical countries.

"Apart from protecting the seagrass, scuba divers and owners of recreational boats should be told about the negative effects of human feeding the turtles," concluded the expert Lluís Cardona.