if that were the case, you would expect the migrations to have ended with the slave trades. However, humans are not a typical food source for any kind of shark. Only about 10 people a year are killed by sharks and its usually a case of misidentification. People on surfboards or flotation devices, for example, can look an awful lot like seals and sea lions, which is a food source to some sharks.
They may be searching for food, or following fishermen, but not following 200 year old trade routes.