I have no idea how long these bones have been here, but visitors to the uninhabited islands (including Fernandina) are not to touch anything, or disturb the ecosystem in anyway, so it is possible they’ve been there quite a long time. They have may been discovered elsewhere on the island and moved to this location for display.
Whales are very important in the human history of the Galápagos. After the islands were discovered in 1535, they were used as a base by privateers in the 1600s. The next group to inhabit them were whalers and fur sealers, beginning in the late 1700s. This was, of course, very harmful for the native populations of whales, fur seals, and even tortoises, which sailors used as food.