Not necessarily. Healthy seals need their daily dose of sun. It is important that they can rest, so do not get to close to them and keep dogs on a leash, so as not to disturb the seals.
A sick seal looks frail and listless and will stay put, even when you come closer. Keep your distance and definitely do not touch the seal. When feeling threatened, it can bite you and transfer germs. Call the Sea Life Centre Blankenberge: 0032 (0)50 42 43 00.
The Management Unit of the North Sea Mathematical Models (MUMM) keeps a database with sightings and beachings of seals and other sea mammals.