JERUSALEM – One-third of the bottlenose dolphins swimming off Israel’s Mediterranean coast are too thin, apparently due to a lack of food from overfishing, researcher said yesterday. A five-year study followed 74 dolphins, who were identified by their dorsal fins, comparable to fingerprints in humans. Photographs showed that ribs were visible in one-third of the dolphins, said Aviad Scheinin, a doctoral student who led the study at the University of Haifa. Many of the 100 to 200 dolphins living off Israel’s shores trail fishing boats, eating the catch that is thrown back into the water. This type of feeding demonstrates the competition between the fishermen and the dolphins, Scheinin said. Israeli fishermen have also reported a drop in the number of fish in recent years. The dolphins could also be suffering from some sort of illness or have a parasite that is causing the problem, Scheinin said. Researchers did not find exceptional levels of pollution, said Dan Kerem, a senior researcher at the Leon Recanati Institute for Maritime Studies at Haifa University, which also participated in the study. One long-term cause could be a drop in nutrients entering the sea from the fertile Nile River after Egypt completed the Aswan Dam in the 1970s, Kerem said. It is hard to determine how long the dolphins’ condition has been poor since no research was conducted before this study, Kerem said. Bottlenose dolphins in general have not been doing well in the Mediterranean, Scheinin said. Researchers in Greece have found that 40 percent of the dolphins in the area are very thin, he said. However, many other countries in the Mediterranean region have not done local research on their dolphin populations. The researchers are hoping to set up nautical nature reserves in the Mediterranean where fishing would be prohibited, Scheinin said. Scheinin is conducting the research as part of his doctorate on the interaction between dolphins and the local fishing industry. Haifa University and the Israel Marine Mammal Research and Assistance Center also participated in the study.