Good news about gorillas

This taxon is classified as Critically Endangered under criterion A4, a population reduction of more than 80% over three generations (where a generation is estimated as 22 years, D. Cailluad unpubl.). The listing is based on exceptionally high levels of hunting and disease-induced mortality (over 90% in some large remote areas, including the second largest protected population at Minkébé), which combined are estimated to have caused its abundance to decline by more than 60% alone over the last 20 to 25 years. Most protected areas have serious poaching problems and almost half of the habitat under protected status has been hard hit by Ebola. Commercial hunting and Ebola induced mortality are both continuing (even accelerating), threats that are not readily mitigated. If the current Ebola epizootic continues at the same rate and trajectory, then the decline in Western Gorilla abundance in all protected areas is projected to be on the order of 45% for the 20-year period spanning 1992 to 2011 (not accounting for other threat factors such as hunting). Furthermore, gorilla reproductive rates are extremely low (maximum intrinsic rate of increase about 3%, Steklis and Gerald-Steklis 2001). Therefore, even an immediate cessation of Ebola mortality and a drastic reduction in the rate of hunting (neither of which seem likely) would not result in rapid population recovery. Rather, under the most optimistic scenarios, population recovery would require on the order of 75 years (Walsh et al. 2003). Much sooner, perhaps 20 to 30 years into the future, habitat loss and degradation from agriculture, timber extraction, mining, and possibly climate change will become a major threat. Thus, a population reduction of more than 80% over three generations (i.e., 66 years, 1980 to 2046) is likely.

Walsh, P.D., Tutin, C.E.G., Baillie, J.E.M., Maisels, F., Stokes, E.J. & Gatti, S. 2007. Gorilla gorilla ssp. gorilla. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 05 August 2008.