Not at a distance — but yes, within it
On a Dutch beach, almost no one will ever be attacked by a seal. Seals are shy and at every disturbance prefer the water to a confrontation. But that's no reason to write them off as cuddly. A seal is a large, carnivorous predator with a mouth full of sharp teeth, and the few cases where things go wrong really do go wrong. Under the right — or rather, wrong — conditions, they are very much dangerous.
The bite force
A seal's jaws are designed to grip large, slippery prey like cod and salmon and crush vertebrae in a single bite. Measurements show a bite force comparable to that of a rottweiler or a mastiff: between 300 and 500 newtons at the canines. The canines themselves are 2 to 3 cm long and razor-sharp.
A bite to a human hand or calf typically causes a deep laceration, often with muscle and tendon damage. Because it happens with a pressure bite rather than a snapping motion as in a dog, blood vessels and nerves are easily damaged. First aid almost always means: rapid wound disinfection, sutures and preventive antibiotics.
Seal finger
But the physical damage is often not even the most serious part. Any seal bite — even a glancing one or a hand scrape on a tooth — can result in seal finger, an infection caused by Mycoplasma bacteria present in virtually every seal mouth. Standard penicillins don't work; only tetracycline antibiotics are effective. Untreated cases can lead to chronic joint stiffness and functional loss of the fingers — in whaling-era practice, amputation was recommended to stop the infection.
Other diseases are also documented: brucellosis, parapox, influenza H10. A full explanation is in can you pet a seal.
The mass of a grey bull
In the common seal — 80 to 110 kilos — the damage risk outweighs the bite risk. But the grey seal is a different animal. An adult male grey seal weighs 230 to 300 kilos, sometimes more. During mating season (November–January), grey bulls are aggressive towards each other and potentially towards humans approaching their harem. An animal close by and feeling threatened can push itself off a sandbar at considerable speed — closing a few metres in seconds, faster than a human can react.
Cases where things went wrong
In the Netherlands, serious incidents with humans are rare. Most cases involve dogs getting too close to a resting seal and ending up in its mouth — often fatally for the dog. There are, however, multiple incidents abroad involving swimmers and divers:
- In Scotland, several bite incidents with open-water swimmers near grey-seal colonies in the Hebrides and on the Scottish east coast.
- In Norway and Maine (USA), attacks on divers by grey seal bulls during mating season.
- In Antarctica, one fatal case (2003) in which a British researcher was grabbed by a leopard seal — a close, but much more aggressive relative of our seals. Relevant as an illustration of the potential.
None of these incidents involved anyone respecting the minimum-distance rule.
Safety rules that work
- 30 metres minimum distance from a resting seal.
- 50 metres from a pup (the mother may return).
- 150 metres with a boat (a legal requirement in the Wadden region).
- Keep dogs on the leash; loose dogs are the main damage source in the Netherlands.
- Never get between a seal and the water. You block its escape route and trigger a defensive reaction.
- Be visible but calm. No sudden movements, no shouting, no drones low overhead.
- If in doubt: call a warden. See seal pup protocol.
For the broader context of human-seal interactions: protection and behaviour rules and responsible seal spotting.
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