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Sources

Where the facts come from

Every factual claim links to its source. This is the full list, and every place where the sources disagree.

How we checked

Each fact was written alongside its source. Our build script stores the source text and checks that the key words and figures appear in it. 46 checks on the last build. Sources read on 5 Nov 2026. Figures that can change carry “checked 5 Nov 2026”.

Main sources: the Natural History Museum, the Sea Mammal Research Unit / SCOS, the Mammal Society, MarLIN, NatureScot, the UK Marine Strategy update, NAMMCO and the IUCN Red List.

When sources disagree

Where trusted sources give different figures, we show them all.

Harbour seal dive depth

One source gives a typical feeding depth; another gives a maximum recorded depth. Both can be true.

How many grey seals around Britain?

The Natural History Museum’s “about 120,000” is a population round figure; SCOS’s 79,122 is annual pup production, not the same thing.

Grey seal dive times

  • Grey seals usually stay underwater for about four to eight minutes; the longest recorded dive in Mammal Society notes is about 30 minutes. Mammal Society: Grey seal

Ordinary dives of a few minutes sit alongside rare long dives of about half an hour.

Harbour seal Red List vs UK trend

Least Concern worldwide or in Europe can still mean serious local declines — as in much of the UK.

Scotland’s latest counts vs UK totals

NatureScot’s scaled August counts and SCOS’s UK composites cover different years and methods; do not treat them as one number.

All sources (11)