Monitoring Marine Turtles on Rapa Nui

Monitoring Marine Turtles on Rapa Nui

Monitoring Marine Turtles on Rapa Nui

By Rocío Álvarez & Camila González – Esmoi

Sea turtles are migratory animals which cover thousands of kilometers (miles) between their breeding grounds and their feeding grounds. They are also philopatric, which is to say that, after many years, they are capable of returning to the same place where they were born for reproduction. This allows us, with modern tools of genetic science, to trace the birth origin of sea turtles even while they are in their feeding grounds, where they can stay for many years.

Rapa Nui is a feeding ground for the green sea turtle (Chelonia mydas) and the hawksbill sea turtle, (Eretmochelys imbricata), both species considered in danger of extinction. Since 2014, Camila González-Johannes, a diving instructor at the
ORCA Diving Center, with the support of Dr. Rocío Álvarez, a veterinarian and researcher with the Ecology and Sustainable Management of Oceanic Islands – ESMOI, is leading a program of photo-identification of the sea turtles on the Island. The
project is based on recognition of individuals through underwater photographs, which show the pattern of facial scales on both cheeks and the scars on the shell, fins and head (Figure 1). To date, we have been able to estimate around the Island a total of 41 green sea turtles and, at least, 4 hawksbill sea turtles.

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In June of this year, both led an awareness campaign on the need to protect turtles. This campaign was financed by ESMOI and aimed at children from the Lorenzo Baeza Vega and San Sebastián de Akivi schools, public institutions and diving centers (Figure 3). With the authorization of the Sea Council, the manual capture of sea turtles is published in early November with the participation of fishermen, freedivers and local divers (Figure 4). The objective was to study the origin of the Rapa Nui turtles through genetic analysis and investigate their diet. In addition, data on age, sex, weight, measurements, health status and biological samples were obtained. Each specimen was marked on the front fins with a metal identification plate (Figure 6) that allows us to track the animals in time and also in the present place.
20 individuals were captured, 16 were juveniles and 4 adults, of which 3 were females and 1 male (you can only know the sex of adults according to the size of their tail). The sizes (length of the carapace) varied between 49cm and 99 cm and the weight between 15 kg and 138 kg. Almost 50% of the individuals presented injuries and fractures in the carapace associated with collision with boats (Figure 7). Although all the turtles exhibited a good body condition and absence of ectoparasites, two showed lesions on the head and fins, possibly infectious. One specimen presented malformation in the carapace possibly associated with malnutrition; another had lost the vision of the left eye because of a hook. Another presented with lesions suggestive of Fibropapillomatosis, an infectious disease associated with marine pollution and high temperatures. Of the total of turtles monitored, 15 were classified as clear morphotype, which possibly have their natal origin in the Western Pacific (eg: Australia, Indo-Pacific) and 5 corresponded to the melanic morphotype, whose origin is associated with the Eastern Pacific (Ex: Galápagos, Mexico). The confirmation will be obtained through genetic analysis, currently in process.

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Preliminary results of the present state of the sea turtles of Rapa Nui strongly suggest a the necessity of greater care of these animals. Our responsibilities, both of the local community and the visitors, is to not feed them, not bother them, respect adistance of at least 5 meters (16 feet) when we are swimming or diving with them and to dispose of our rubbish in the proper places. Our discoveries also underline the relevance of collecting scientific information for zoning the new marine protected area (AMCP-MU), taking into consideration the resting sites and feeding grounds
of the turtles. In addition, we need to study the diseases that could be contagious between animal species and human beings (zoonoses) and systematically monitor the quality of the water in the coastal areas that have the greatest human traffic, since the turtles can serve as biological indicators of environmental contamination.
We hope to shortly have the results of the genetic analysis and the dietetic information to continue monitoring the turtles in collaboration with the local
community. Only by studying their ecology, their origin and their conservation can we propose alternatives for their protection which will permit us to maintain the
population of sea turtles over the long term, both on a local level as well as in our region of the Pacific Ocean. We should never forget that on Rapa Nui, as in other
islands of Polynesia and the Pacific, the sea turtles have been part of the cultural identity since ancient times and are represented in the art, mythology, symbolism, popular traditions and in ritual and spiritual life.

So please, visitors … Leave your rubbish in the appropriate places. Don’t feed the turtles or any other marine species. Respect the ocean and all its biodiversity. Don’t forget that it is part of our natural heritage.

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