The brown rat with white patches (not dots) was foraging for food on the beach. The rodent was feasting on the little creatures that are usually found in rock pools.
On the opposite side of the bay, there was another white rat. These must have been pets that either escaped or else were let loose as the wild rats commonly seen in the area are grey/brown in colour.
They usually come down to the beach because they can always be sure of a fulfilling and nutritious meal at any time but they normally venture out before nightfall when the beach quietens down.
Many beach-goers are selfish enough to leave bits and pieces of food and fruit on the rocks, even though there are bins provided. Perhaps if the rats developed a penchant for nibbling at the cigarette ends, which are always in plentiful supply, they might die a little faster!