08 May 2011

Studying bottlenose dolphins in a semi-closed basin exposed to acute anthropogenic impacts

When we started our work in the Northern Evoikos Gulf, central Greece, all we knew came from a 2003 scientific article written by the late Dimitris Zafiropoulos — a pioneer of dolphin research in Greece — together with his wife Livia Merlini (1). Dimitris and Livia reported an extremely high density of bottlenose dolphins in these waters.

As of 2010, we had been studying dolphins in the several areas of Greece, as well as in Italy and Croatia. The Northern Evoikos Gulf was a portion of Greece that had long stimulated our interest. We wanted to describe the present conservation status of dolphins in an area of high human impact and compare it with situations found in other places. Such approach can ultimately increase our understanding of cetacean ecology as well as of their responses to human pressures.

Thanks to OceanCare — our main funder and supporter — in October 2010 we set up the logistics and started surveying the Gulf with a small inflatable boat provided by the Tethys Research Institute. Soon after we started our work at sea, it became clear that the density of dolphins was nowhere near that described by Zafiropoulos and Merlini in their early publication. We actually spent 22 hours of navigation across four days before spotting the first dorsal fin.  By that time we were quite depressed by such a low density of animals.

It took us ten days to survey the whole western side of the Gulf, our efforts being often frustrated by wind and rain. With a single dolphin sighting in our logbook, we then moved on to surveying the eastern side. The Northern Evoikos Gulf is a large portion of sea, encompassing 1300 km2 (i.e. 14 times the size of Lake Z├╝rich).  Therefore, we had to move the boat to the port of Larymna, which looked like an appropriate base. We quickly realized that the waters near Larymna were a dolphin hotspot.

Larymna houses an enormous ferronickel smelting plant, which produces industrial smokes and tonnes of slag 24 hours a day, 365 days a year — since the 1960s.  Operating within such a spoiled area brought unexpected difficulties, because the air was thick with toxic smokes and quite hard to breath on some days. Still, it was good to find dolphins relatively easily, including close to the smelting plant, where the animals were feeding near the fish farms present in the bay. The dolphins actually seemed to spend considerable time feeding in polluted waters, often wrapped themselves in clouds of toxic smoke.

We returned to the Gulf in April and May 2011, carrying out a number of surveys. By the end of the study we had totalled 3632 km of navigation and spent a total of 25 days with 158 dolphin groups of different size and composition. We also took about 6000 photos of the dolphins, which allowed for the individual identification of approximately 100 animals based on the natural marks on their dorsal fins. A rigorous estimate of dolphin abundance in the Gulf is underway, but based on the preliminary infromation we collected, roughly 100-150 animals may live in these waters. Based on the re-sighting pattern, it appears that most dolphins are highly 'resident' there.

The problem is — most dolphins seem to reside in the most polluted portion of the Gulf. They spend hours feeding around the fish farm cages near the smelting plant, then rest and socialize while moving away from the noisy and polluted spots, only to return to the fish farms on the following day.

Several animals carried pathologies and deformities, to an extent that was not seen by us elsewhere in the Mediterranean Sea. An individual, nicknamed 'Bubbo', had a large melon-sized swelling on one side of its body. 'Pirulo' had an impressive deformity of the tail stock. Quite a few others had growths and skin diseases. To our surprise, however, they were all active and energetic, including while they were feeding among the fish farms buoys (some animals were seen socializing and mating only metres away from screaming workers and noisy barges). An individual with 3 metres of rope attached to his flukes would sometimes come to bow-ride, while another with an amputated dorsal fin was among the most acrobatic, often performing stunning leaps while interacting with friends. Even Bubbo and Pirulo seemed to be doing well, socializing with other animals as if their pathologies would not matter.

A remarkable aspect of working in the Northern Evoikos Gulf is that here the ugliest and most polluted places are found close to areas of incredible beauty. You feel like you are in hell, then turn around a headland and find yourself in the most beautiful and pristine-looking bay. However, the nice places seem to have a lower density of dolphins. This may be related to what appears to be the second serious problem in the Gulf, besides pollution: overfishing by purse seiners and trawlers. The fleet of purse seiners is incredibly large, every port of suitable size being stuffed with these boats. At times we have seen up to 15 purse seiners fishing in the same small portion of sea. In the winter, bottom trawlers drag their nets on the sea floor, over and over, including near the coast where such fishing is prohibited. Our observations in the Gulf therefore tell a story of high and probably unsustainable fishing pressure.

The relatively low density of dolphins found by us, compared to that reported by Zafiropoulos and Merlini a decade ago, may be related to declining prey resources. This would also explain why the dolphins spend so much time feeding near finfish aquaculture plants — productive areas where wild fish is predictably more abundant — but they are not found in other portions of the Gulf that are likely overexploited by commercial fishing fleets. Prey depletion may have resulted in habitat loss and dolphins must now rely on wild fish attracted by fish farms, whereas in polluted waters. Bottlenose dolphins (like seagulls, foxes and — all too often — humans) seem to care little about pollution and much about food. You may find these animals in the most polluted places as long as fish is locally available. That, of course, does not mean they are immune to disease.
In the Northern Evoikos Gulf we did not find a dolphin heaven. Yet, we discovered a place where an interesting story can be told about wildlife being forced to adapt to human pressures, producing the intriguing kind of contrast that we tried to depict in the digital photo book posted at: 

(1) Zafiropoulos D., Merlini L. 2003. A comparative ecological study of bottlenose dolphins (Tursiops truncatus) in South and North Evvoikos Gulfs. Proceedings 8th International Conference on Environmental Science and Technology, Lemnos Island, Greece, 8-10 September 2003. Vol. B: 921-925.

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