In 1975, newspapers reported that oil pollution from shipwrecks and the pumping of bilges at sea had killed tens of thousands of African penguins. At the time, the Dassen Island colony was being passed by 650 oil tankers each month. In 1979, an oil spill prompted the collection and treatment of 150 African penguins from St Croix Island near Port Elizabeth. The animals were later released at Robben Island and four of them promptly swam back to St Croix Island, surprising scientists. In 1983, the exposure of penguins of Dassen Island to the oil slick from the Castillo de Bellver was also a controversial topic at the time given their conservation status at the time, but owing to prevailing wind and current, only gannets were oiled. African penguin casualties were significant following the sinking of the MV "Apollo Sea" and subsequent oil slick in 1994. 10,000 penguins were collected and cleaned, of which less than half survived. Disaster struck on 23 June 2000, when the iron ore tanker MV "Treasure" sank between Robben Island and Dassen Island, South Africa. It released 1,300 tons of fuel oil, causing an unprecedented coastal bird crisis, oiling 19,000 adult penguins at the height of the best breeding season on record for this vulnerable species. The oiled birds were brought to an abandoned train repair warehouse in Cape Town to be cared for. An additional 19,500 un-oiled penguins were removed from Dassen Island and other areas before they became oiled, and were released about 800 kilometres east of Cape Town, near Port Elizabeth. This gave workers enough time to clean up the oiled waters and shores before the birds could complete their long swim home (which took the penguins between one and three weeks). Some of the penguins were named and radio-tracked as they swam back to their breeding grounds. Tens of thousands of volunteers helped with the rescue and rehabilitation process, which was overseen by IFAW (International Fund for Animal Welfare) and the South African Foundation for the Conservation of Coastal Birds (SANCCOB), and took more than three months to complete. This was the largest animal rescue event in history; more than 91% of the penguins were successfully rehabilitated and released – an amazing feat that could not have been accomplished without such a tremendous international response. Due to the positive outcome of African penguins being raised in captivity after tragedies, such as the "Treasure" oil spill, the species is considered a good "candidate for a captive-breeding programme which aims to release offspring into the wild"; however, worries about the spread of new strains of avian malaria is a major concerning factor in the situation.