Complex sentence: Due to the severe pressures faced by the deer the IUCN has twice listed it as an endangered species: firstly in 1994 (when it was de-listed within the year) and again in 1996 (which listing has continued until the present).
Split into simpler sentences: Due to the severe pressures faced by the deer the IUCN has twice listed it as an endangered species. First in 1994 (when it was de-listed within the year) then in 1996 (which has continued until the present).