Fishing, seabird fowling, and the exploitation of marine mammals persisted in settlements around the coast and islands of western and northern Scotland from prehistoric times until the twentieth century. Until the mid-first millennium ad most fishing focused on immature saithe and was carried out close to the shore, but from Norse times onwards intensive deep-sea fishing for cod took place and, in the Hebrides, a herring fishery developed. Seabirds were a minor but regular part of subsistence; some were harvested from breeding colonies and others caught more casually, often in association with fishing. Marine mammals provided food and oil; whalebone was an important raw material. As well as exploiting stranded whales, people hunted seals from their breeding sites and small cetaceans by herding them into bays and inlets.