Whilst the Cape Colony might well have possessed slaves, the establishment of Port Elizabeth came at the culmination of the emancipation efforts by the British government. Hence the prevalence and practice of slavery was not of such great importance as it was closer to Cape Town.
In 1807 the British government banned the slave trade to all her colonies, including the Cape. This meant that no more slaves (from any destination) could be sent to work in the Cape. However, those who were already in the Cape continued to work as slaves until 1834 when all slaves in the British Empire were to be emancipated. Many of the slaves chose to remain on with their owners while some started a new life in and around Cape Town working as tradesmen. Gradually these people became absorbed into the Cape community.
Main picture: The reality of slavery