Task: Question Answering
Input (English): Passage: The traditions of the local peoples are unanimous in affirming that the oldest inhabitants of Casamance are the Bainuk people and that the left bank of the mouth of the river was first populated by the Jola. Portuguese sailors reached the west African coast in the 15th century, and in the 16th century, Portuguese traders became active in the Casamance region, mostly in search of wax, ivory, and slaves. They did not linger on "Mosquito Island", instead founding their first trading post at Ziguinchor in 1645.In the late 1820s, a mulatto trader from Gorée, Pierre Baudin, moved to Itou and began planting rice and producing lime by crushing the shells of mangrove oysters and cooking them in lime kilns. The French administration treated Baudin as their representative on the island and did not send others because few of the French wanted to live on the island. Being wet and marshy, Carabane had a reputation for its poor sanitation. The local economy was based mainly on weedy rice, which was sold in Ziguinchor or to the British in The Gambia. The Baudin family used slaves to produce the rice and, despite the declaration of its official abolition in the French colonial empire in 1848, slavery continued on the island until the early 20th century.The colonial administration wanted to expand its influence around the river, particularly because the inhabitants of Gorée were threatened with losing part of their resources with the imminent demise of the slave trade, and also because of their competition with Saint-Louis. On January 9, 1836, Lieutenant Malavois, who was in charge of Gorée, left for Casamance in search of a site for a trading post. The tip of Diogue, on the north shore, was first considered, but at the refusal of the Jola, it was the opposite bank which was eventually accepted. 
Question: What practice continued on the Island until the early 20th century?
Output (English): slavery.