I HAD never given much thought to how dolphins copulate, much less seen them doing it. But in a frenzied, water-churning few minutes in the Amvrakikos gulf, western Greece, I witnessed a cetacean orgy. We had already spotted an incredibly cute newborn dolphin and several calves, so I assumed that the dolphin population here was thriving. As I was to find out, that doesn鈥檛 mean it will stay that way.
I was helping survey dolphins with Joan Gonzalvo of the based in Milan, Italy, and several volunteers on a project organised by the , an international charity that engages non-scientists in scientific research. We were checking up on the highest known density of bottlenose dolphins in the Mediterranean Sea.
While the bottlenose dolphin (Tursiops truncatus) population in the Amvrakikos gulf seems to be stable, those in other parts of the Mediterranean have crashed as overfishing and pollution have wiped out their food supplies. Many are worried that the Amvrakikos dolphins could be next. 鈥淭he density is high and the population is stable but small, so in this increasingly degraded ecosystem the dolphins are vulnerable,鈥� says Gonzalvo.
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鈥淚n this increasingly degraded ecosystem the dolphins of Amvrakikos gulf are vulnerable鈥�
The Amvrakikos gulf is an inlet of the eastern Mediterranean that covers 400 square kilometres (see map). With an opening into the Ionian Sea that is only 370 metres wide and as shallow as 5 metres in places, the gulf is practically enclosed, just like the Med itself, which has a narrow opening into the Atlantic Ocean at the Straits of Gibraltar. 鈥淚t鈥檚 a natural laboratory,鈥� says Gonzalvo.
As with the Mediterranean, water turnover in the Amvrakikos gulf is very slow, taking several years to be replaced completely. In effect, it鈥檚 a giant bathtub. Gonzalvo fears the gulf is facing a similar ecological fate as the Med 鈥� being choked to death by pollution.
Gonzalvo should know. He used to work in what he calls 鈥減aradise on Earth鈥� 鈥� the waters surrounding the Greek island of Kalamos. He was there to witness the crash in population of the common dolphin (Delphinus delphis) from 150 animals in 1996 to almost none in 2007. Tuna, swordfish and other large fish species declined over the same period (Endangered Species Research, ). 鈥淲hen the common dolphins鈥� food disappeared as a result of overfishing, the dolphins vanished,鈥� says Gonzalvo.
Industrial fishing is banned in the Amvrakikos gulf as . Yet it is still becoming increasingly degraded. Like many parts of the Med, there is no sewage treatment, so raw waste is pumped directly into the water. The gulf also contains 24 fish farms with between them, each producing nitrogen-rich waste, and a number of rivers with high nitrogen run-off in the form of fertilisers flowing into it. Add this together and eutrophication is a major threat: the water is murky and oxygen levels decline to near zero below 20 metres.
Sardines are the dominant fish species in the gulf, and it seems that the bottlenose dolphins of Amvrakikos have been able to adapt their diets to feed on these smaller fish. We saw their feeding methods: the dolphins would twist in the water and scoop fish up their bellies into their open mouths. It鈥檚 exhilarating to watch. But if the water鈥檚 oxygen levels decline enough to drive the sardines out, the dolphins will disappear too, says Gonzalvo. 鈥淭he priority is to curtail pollution,鈥� he says.
Increasing water pollution and their isolation from the rest of the Med make this stronghold of dolphins a conservation priority. And, for the record, dolphins mate belly-to-belly.
