Mild winters blamed for dolphin deaths

日期:2019-03-03 05:09:11 作者:壤驷跺 阅读:

By ANTHONY LUKE in MARDRID Spanish biologists are blaming recent warm winters for the epidemic that killed hundreds, perhaps thousands, of striped dolphins in the Mediterranean last summer. According to Alex Aguilar of Barcelona University, who is president of the European Cetacean Society, two successive mild winters with relatively little rain dramatically reduced food stocks in the Mediterranean, leaving the dolphins with weakened immune systems that lowered their defences against two deadly viruses: distemper and herpes. ‘What struck us immediately on examining some of the 550 corpses washed up on beaches along the southeastern coast of Spain, was their inordinate lack of blubber,’ says Aguilar. His team of marine biologists now believes that as the dolphins were starved of food they mobilised their fat reserves. This released toxic polychlorinated biphenyls (PCBs) that had accumulated in their fat, freeing them to enter the bloodstream. ‘The PCBs further weakened the hungry dolphins and from what we have seen of liver samples taken from the dead animals, herpes and then distemper did the rest,’ Aguilar concludes. After several attempts to explain what caused the deaths last summer, Aguilar’s investigations revealed the presence of parasites, PCBs and the two viruses. But he said the fifth factor – the meteorological one – baffled him for months. Under normal conditions, healthy dolphins would not succumb to the viruses or PCB poisoning. Reviewing weather patterns over the past two winters, Aguilar found that the production of nutrients in the sea which were normally stimulated by cold weather had been reduced, and because of the shortage of rain, little organic matter from land was flushed into the sea. Winds that usually drive local currents also failed to blow. ‘There was nothing to stir up what nutrients there were from the lower, more productive depths of the sea,’ he said. Aguilar thinks a sixth, unidentified factor was also at work. Most of the dolphins that washed up on the Spanish coast came ashore within a triangle formed by Valencia, Alicante and the Balearic Isles, where the greatest concentration of tourists are. ‘The epidemic here was particularly virulent,’ Aguilar says, ‘but we have yet to determine whether this was due to pollution, the total collapse of nutrients production, the massive presence of the viruses or what.’ No one will ever know how many dolphins died. Some biologists suggest that for every corpse washed ashore, 10 more probably died at sea. After discussions with fishermen and the crews of research ships, who have spotted dozens of dead dolphins at sea, Aguilar agrees that the corpses found on beaches must be only a small percentage of the total. According to Aguilar,