Elephant decline in Lake Manyara National Park, Tanzania

The population of African elephant (Loxodonta africana (Blumenbach)) in Lake Manyara National Park, northern Tanzania, declined from about 500 individuals in 1984, to about 150 in 1988 due to poaching (mortality rate about 60% p.a.). In 1991 the population had declined further to about 60 individuals (mortality rate about 30% p.a.). In 1984 and 1991 road counts in the park were conducted. In 1984 a total distance of 2705 km was covered which yielded sightings of 777 elephant groups. In 1991 this distance was 5486 km and only 53 groups were observed. In both years an average elephant was seen in a group of seven individuals. Poaching pressure, apparently, had no effect on average group sizes. Group size changes with season, both in 1984 and 1991. The smallest groups were observed during the dry season when Acacia tortilis pods provided a defendable resource.In 1984, elephant occurred significantly more than expected in groups of five-nine individuals and less than expected in groups of one or two individuals or in groups larger than 16. This has been interpreted as a confirmation of the family structure of elephant as reported in other studies. In 1991, elephant group sizes were distributed according to a model of random association of individuals, indicative of destruction of the social framework by poaching.