The arrival of 600 colonists from Norfolk Island between 1807 and 1813 increased tensions as they established farms along the River Derwent and east and west of Launceston, occupying 10 percent of Van Diemen's Land. By 1814 12,700ha of land was under cultivation, with 5000 cattle and 38,000 sheep. The Norfolk Islanders used violence to stake their claim on the land, attacking Aboriginal camps at night, slaughtering parents and abducting the orphaned children as their servants. The attacks prompted retaliatory raids on settlers' cattle herds in the southeast. Between 1817 and 1824 the colonial population rose from 2000 to 12,600 and in 1823 alone more than 1000 land grants totalling 175,704ha were made to new settlers; by that year Van Diemen's Land's sheep population had reached 200,000 and the so-called Settled Districts accounted for 30 per cent of the island's total land area. The rapid colonisation transformed traditional kangaroo hunting grounds into farms with grazing livestock as well as fences, hedges and stone walls, while police and military patrols were increased to control the convict farm labourers.