IWC Population (Abundance) Estimates

Estimates of current population size, known as abundance estimates, are derived from a combination of fieldwork and computer modelling. Vessel-based and aerial sighting surveys, acoustic monitoring, and analysis of individual animal markings are techniques used independently or in conjunction with each other to count whales. The information gathered from this fieldwork is used as the basis for population modelling which produces an abundance estimate.

In 2017, the IWC Scientific Committee established a new expert group to review and agree all the Abundance Estimates submitted to the Scientific Committee. This new process ensures quality and consistency across all the estimates used by the IWC.

Click here to read more about the establishment and work of the Scientific Committee’s Working Group on Abundance Estimates (ASI).

It is impossible for cetacean abundance estimates to be completely precise and IWC estimates are presented as a ‘best estimate’ figure, accompanied by a 95% Confidence Interval, showing a range of plausible values for the population’s actual abundance. As an example, the table below shows that the 1991/92-2003/4 abundance estimate for Southern Hemisphere blue whales is 2,300 with a 95% confidence interval of 1,150-4,500. This means that the range 1,150-4,500 was computed using a method that has a 95% chance of including the population’s actual abundance.

Increases or decreases in population are indicated within the table, where these have been identified.

At present the IWC has agreed estimates only for some species/areas. With the establishment of the ASI group it is planned to update this table and fill in the gaps where possible.

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