Study

Estimates of the current global population size and historical trajectory for sperm whales

Whitehead, Hal

Marine Ecology Progress Series, 2002

Peer-reviewedmodelling studywild

What they did

Sperm whale densities from visual and acoustic surveys across a large fraction of the world ocean were extrapolated to global scale, and combined with catch records to reconstruct the population trajectory through the whaling era.

Studied in: Physeter macrocephalus
Sample size: visual and acoustic survey data extrapolated globally

What they found

The global population is estimated at around 360,000 animals, roughly a third of the pre-whaling level. Recovery since the end of large-scale whaling appears slow, consistent with the species' very low reproductive rate — a single calf every four to six years, with long maternal care.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Sperm whales remain substantially depleted, and their life history makes recovery slow even in the absence of continued hunting.

How NatureHQ reads it

Two things are worth taking from this and they sit awkwardly together. The species is not on the brink — several hundred thousand animals is a large population, and sperm whales are not among the most endangered whales. And it is at roughly a third of what it was, with a reproductive rate so slow that a century is not long for recovery. Both matter, because conservation coverage tends to pick one and drop the other. The estimate itself carries wide uncertainty: most of the ocean is not surveyed, and the global figure is an extrapolation.

Limitations

Global extrapolation from surveys covering a minority of the ocean, with wide confidence bounds.
Historical catch records are incomplete, particularly from Soviet whaling.
Later assessments have revised regional figures in both directions.