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Comprehensive Assessment: North Pacific Humpback Whales

 In March, a small group of Scientific Committee specialists will gather in Seattle, USA, to complete the next stage in a comprehensive assessment of North Pacific humpback whales.

Comprehensive assessments provide the Commission with information on the current status of a particular whale population within a particular region, usually an ocean basin. The assessment tells the Commission whether that population is recovered, recovering, or cause for concern. It also identifies any factors that may affect the current status. 

The process has several stages, beginning with a review of existing information and identification of key information gaps. 

Understanding the structure of the population is a key component of this stage. Just as one species may exist in a number of different populations around the world, the population in one ocean basin may be divided into different sub-populations, also known as ‘stocks.’ Even within a relatively small area, some stocks may be healthy whilst others are not, so it is important to understand, as far as possible, how the stocks are structured. It is hard to establish stock structure with complete certainty and so scientists often recommend several alternative hypotheses, each of which is incorporated into the assessment.

Other information required to conduct the assessment includes:

- estimates of the current and past size of the population

- estimates of current and past removals from the population: deaths caused by impacts such as hunting, bycatch or ship strikes

- biological information such as growth rates, age of sexual maturity and male/female ratios

- environmental information 

This information is obtained from a wide range of data sources such as genetic research, satellite tagging programmes, sightings surveys and photo-ID catalogues. Some of this information may exist already but much must be commissioned as part of the Comprehensive Assessment.

All available data are collated and used to develop a series of plausible scenarios relating to the recommended hypotheses on stock structure; these are tested using computer modelling and population models are developed based on each stock structure hypothesis. The analytical approach also includes tests to incorporate levels of uncertainty, inevitable in work that is reliant on many different types of estimate.

The Comprehensive Assessment of North Pacific Humpback whales began in 2016. Work since then includes analyses of genetic data and abundance, and use of an automated photo-ID algorithm to facilitate a large-scale photo-ID matching exercise. A number of refinements have been made as new data became available. New satellite tag research is also now being incorporated, which analyses data from tags deployed across both breeding and feeding grounds of the North Pacific humpbacks over a thirty year period.

The group has already established and recommended two hypotheses for stock structure in breeding areas and two separate hypotheses for stock structure in feeding areas. The workshop in March will continue the computer modelling work and report to the next meeting of the Scientific Commission which begins in April.