An 80 foot long fishing vessel sank in the harbour at Pago Pago,American Samoa.   The old vessel had been moored in the harbour when it sprung a leak and sunk.   No reports of injuries, but some 4000 litres of oil spilled into the harbour.   Authorities placed an oil boom around the vessel to contain any further pollution escaping into the harbour.   The Coast Guard has started clean up operations and has arranged salvage to refloat the vessel.