Lion populations throughout many parts of Africa have declined sharply since the early 1990s and are likely to shrink by half again in the next two decades unless a major conservation effort is mounted to save them, a new study has found.

The study, which analyzed data from 47 of the 67 African lion populations totaling an estimated 8,221 lions, found pronounced reductions in West and Central African populations — in two national parks, Comoé and Mole, the animals appeared already to be extinct. There were less drastic but still substantial declines in the East African countries where lions have traditionally thrived.

Over all, the African lion population in these regions has decreased by about 50 percent since 1993, said Luke Hunter, president of Panthera, an organization focused on the global conservation of big cats, and one of eight authors of the study, published this week in the journal Proceedings of the National Academy of Sciences.

In contrast, most populations in Southern Africa remained stable or even increased over the same time period; an exception was a large population in the Okavango Delta, in Botswana, which declined.