Why Seal Identification Matters
Family: Phocidae
Along many North Atlantic coastlines, particularly around Scotland, observers frequently encounter two common species: Grey Seals [Halichoerus grypus] and Harbour Seals (also known as Common Seals) [Phoca vitulina]. Distinguishing between them is not always intuitive for beginners, and occasional sightings of Arctic species such as harp, hooded, bearded, or ringed seals can add to the confusion.
Accurate identification is valuable for wildlife monitoring, conservation surveys, and responsible public engagement with marine mammals. Understanding visible differences helps observers collect meaningful sightings without disturbing animals.
Start with the Head: Shape and Facial Features
When only a seal’s head is visible above water, facial structure provides strong clues.
- Long, flatter Roman nose profile
- Eyes positioned midway along the head.
- Often shows a distinctive double chin.
- Overall, the head shape appears elongated from front to back.
- More rounded or dished facial profile
- The eyes and mouth are located toward the front of the face.
- Shorter, compact head shape
These head shape differences are among the most reliable field markers when full body views are unavailable.
Size Differences: The Quick Visual Estimate
If you can observe the whole animal, overall body length is informative.
- Grey seals: approximately 1.8 to 2.1 meters as adults
- Harbour seals: typically 1.3 to 1.7 meters
Grey seals are generally larger and more robust; however, size comparisons are most effective when animals are observed side by side or frequently enough to develop a sense of scale.
Coat Patterns and Seasonal Appearance
Coat coloration, known as pelage, varies by species and season.
- Usually evenly spotted across the body
- Spots are relatively consistent and fine.
- Contrasting pale underside and darker back
- Larger, irregular blotches or spots
- Males are often darker than females.
However, pelage can be misleading. A seal’s coat may look dramatically different depending on whether it is wet or dry and during annual moulting periods. Grey seals typically moult between December and March, while harbour seals moult between July and September.
Pupping Season: Behavioural and Timing Differences
Reproductive behaviour offers another clear distinction.
- Give birth between September and December.
- Use remote beaches or islands above the high water line.
- Mothers remain ashore for several weeks with white-coated pups.
- Pup earlier, usually June to July
- Choose sandbanks or rocky intertidal areas.
- Pups are born with spotted coats and can swim within hours.
These differences in pup development and timing reflect distinct life history strategies between the two species.
Movement, Grouping, and Sound Clues
Observing behaviour can support identification when visual cues are limited.
- Grey seals tend to lie closer together when hauled out in groups.
- Harbour seals often maintain more spacing.
- On land, harbour seals wriggle forward, while grey seals appear to bounce.
- Vocalizations differ. Haunting howls often indicate grey seals, while harbour seals are comparatively quiet.
Grey Seal Haunting Call:
Conclusions: Grey Seal vs Common Seal – A Multi-Factor Approach
No single feature guarantees accurate identification. Instead, combine multiple observations.
- Head shape and facial structure
- Relative body size
- Coat pattern and coloration
- Pupping timing and habitat
- Behavioural cues such as movement and sound
Using several indicators together improves confidence, particularly when environmental conditions or viewing distance limit clarity.
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References
- Costa, D.P. (Daniel P. and McHuron, E. (2022) Ethology and behavioral ecology of phocids. 1st ed. Edited by E.A. McHuron and D.P. Costa. Cham: Springer. [Accessed 13/02/2026]
- Perrin, W.F., Würsig, B.G. and Thewissen, J.G.M. (2009) Encyclopedia of marine mammals. 2nd ed. London: Academic. [Accessed 13/02/2026]
Citations
- Sea Mammal Research Unit, University of St Andrews — Identifying Seals Leaflet (2016). [Accessed 13/02/2026]
