ILLEGAL dumping of cargo oil at sea could have caused the deaths of hundreds of sea birds along England's south coast, an expert from Southampton said.
Thousands of birds have been washed to shore along coastline that stretches from West Sussex to Cornwall - including Hampshire and the Isle of Wight - after being covered in a sticky, oily substance.
Wildlife experts and volunteers raced to the shoreline to save as many birds as possible, and hundreds - mostly guillemots - are now being treated at RSPCA centres.
Scientists from the Environment Agency identified the mystery substance as a refined mineral oil, but not from an animal or vegetable-based oil.
One expert said the oil could have been discharged into the sea accidentally or deliberately.
''Some kind of accident such as a leaky gearbox or a broken pipe is the most likely cause of a mineral oil spill, but it is unusual that it would cause this much havoc,'' said Dr Simon Boxall, an oceanographer at the University of Southampton.
''So that makes one think it could be an illegal dump of cargo oil - oil that is being transported rather than used in the working of the ship.
''This could happen if there was illegal washing out of tanks at sea. Some unscrupulous operators, and they are rare, flush the tanks out there because it is cheaper and easier than doing it in dock. It is illegal and quite harmful.
''Ships use lots of different mineral oils for working. You've got oil in the engines, a lot of hydraulic fluids, in the anchor winches, ship's cranes and so on.
''Until the Coastguard Agency can pinpoint the slick, and the size of the slick, it will be hard to know. Tracking it down is no easy task. A small slick is more likely to indicate an accident, a larger slick may mean oil has been dumped.''
Wildlife staff are expecting to see more guillemots and razorbills come ashore over the weekend and say it is crucial that the source is found.
Staff at the RSPCA West Hatch centre near Taunton, Somerset, are treating the birds using margarine and washing up liquid to clean the substance from their feathers.
The centre was caring for almost 170 birds, and while numbers of dead birds are as yet unclear, one RSPCA officer said that for every live bird that is taken off the beach there can be up to nine others that have died at sea.
The Southampton-based Maritime and Coastguard Agency (MCA) said it is regularly called upon to react to a wide range of incidents and to develop a response to deal with emergencies at sea that cause pollution or threaten to cause pollution.
A spokesman added: ''This occurrence of seabirds being washed up on south coast beaches contaminated with a product is rare and we are working with partner organisations and agencies to deal with this event.''
Environment minister Richard Benyon added: ''I have spoken with the Maritime and Coastguard Agency and every effort is being made to identify the cause of this problem.
''I'd like to thank everyone involved in helping the seabirds affected and it's thanks to their efforts that many have been cleaned up and now have a chance of survival.''