Extinction risk and exploited populations

Douglas Crookes


A number of years ago I had the opportunity to visit Kakum National Park in Ghana, home of the endangered Diana monkey, giant bongo antelope, yellow-backed duiker and African elephant. I had hoped that it would afford me the opportunity to see some of the region’s endemic fauna. Sadly, all that I managed to experience was the ‘empty forest’ syndrome. The rainforests were spectacular, don’t get me wrong. But the shy mammals were nowhere in sight.


Once, the Upper Guinean rainforest was teeming with wildlife. But logging and overharvesting have reduced wildlife populations significantly. These days, the last vestiges of most fauna in the area have retreated deep into the closed canopy forests and are rarely seen. The only exceptions are a number of smaller bodied mammals that have adapted to human presence.


This trend is not limited to West Africa. Recently, conservationists have expressed concern that a sixth global mass extinction may be occurring. The recent Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services [IPBES] report found that 25% of species globally are threatened with extinction, and that direct exploitation is a major driver of this extinction risk.

Source: IPBES


The 2019 Kuala Lumur declaration, presented and discussed  by the 1,361 participants  from  87  countries  attending  the  29th International Congress for Conservation Biology (ICCB) held in July 2019  in  Kuala  Lumpur,  Malaysia expressed concern over these mass extinctions and stated that: “A solid evidence base for conservation decisions” was needed in order to combat this loss, built on “solid science”.


The need for rigorous approaches has also been called for to accurately assess the conservation status of species. One example is the northern minke whale. While there is a general moratorium on whaling, the minke whale has been subject to increased harvesting in recent years, notably by Japan who resumed commercial whaling activities in its territorial waters in July 2019. The International Whaling Commission [IWC] said "difficulties in determining stock structure make firm conclusions on status difficult" and called for more research to accurately assess the status of minke whales, and to correctly predict the impacts of commercial whaling on these populations.


A recent paper proposes one such tool to reduce these uncertainties. A framework was developed in order to assess the extinction risk of exploited populations. The framework proposes linking a simple population model with a classification scheme. The framework was tested on nine species across marine and terrestrial ecosystems. Results show that in some instances the tool provides a more conservative assessment of extinction risk compared with the existing IUCN Red list assessment. For example, in the case of the northern minke whale (Balae-noptera acutorostrata), it was assessed by the Red List as ‘Least Concern’, whereas according to our scenario analysis a more appropriate assessment would be ‘Endangered’.

Table 2
The ‘Sus score’ (far right column) is converted into extinction risk classification by matching the ‘Sus score’ categories with the Red list categories.

Caution should be exercised in interpreting the results from this assessment, since the data used are in some instances somewhat dated. However, the results do demonstrate the potential of such a tool for improving the evidence base for conservation decisions related to populations subject to exploitation, thus ensuring that time and resources are directed where they are needed most. In the case of the minke whale, this could mean more stringent legislation and international pressure against whaling.

Minke whale
Figure: Image of a minke whale breaching

The data are all open access, and a simple population model is also provided below that could be adapted to fit a number of different species. The methodology is not under copyright in support of transparent conservation science.

To access the paper that develops this classification scheme please see this link

To download the population model (in Vensim) please see here

To download the Vensim PLE software (free) follow this link


About the author:

Douglas Crookes (douglascrookes@gmail.com) is a British national who has worked in conservation for a number of years. The views expressed here are his own, and do not necessarily represent any institution or organisation.