An estimated 7,000 Cape fur seals have been discovered dead at a breeding colony in central Namibia, scientists said on Saturday.
Conservationist Naude Dreyer of the charity Ocean Conservation Namibia began noticing dead seals littering the sandy beaches of the Pelican Point colony near Walvis Bay city in September.
Then in the first two weeks of October he found large numbers of seal foetuses at the colony, Dr Tess Gridley from the Namibian Dolphin Project told AFP by phone.
Fur seals normally give birth between mid-November and mid-December.
Gridley estimated that between 5,000 and 7,000 female seals had miscarried young with more still being found.
The cause of the mass die off is yet to be established but scientists suspect anything from pollutants or bacterial infection to malnutrition.
Some of the dead females found were "thin-looking, emaciated, with very little fat reserves", said Gridley.
Scientists are collecting samples for testing.
In 1994 some 10,000 seals died and 15,000 foetuses were aborted in a mass die off that was linked to starvation suspected to have resulted from a shortage of fish as well as from a bacterial infection at another breeding colony, the Cape Cross, some 116 kilometres (72 miles) north of the central tourist town Swakopmund.
Annely Haiphene, executive director in the Ministry of Fisheries and Marine resources, told AFP she suspected the seals died from "lack of food" but will wait for the outcome of the tests.