Bonny was a key point for the Slaving trade - slavery and carrying slaves in British ships was illegal after 1 May 1807 but the Southern states of the USA kept slavery until the American civil war officially ended it (one can argue that it didnt really end for a further century after this) - I presume the US still acquired some slaves from Africa.

Captain George Cannon was apparently murdered by his own crew c. 1815 on what is suspiciously like a slaving voyage - many Manx were heavily into slaving (via a Liverpool connection) upto 1807.

It is of course possible that these were involved with the RN anti slavery patrols etc or purely honest trading.