The correct answer is C) The vessel is "engaged in fishing" when she is using fishing apparatus which restricts her maneuverability. This is the correct answer because the definition of a vessel "engaged in fishing" under both the International and Inland Navigation Rules is when the vessel is using fishing gear that restricts its ability to maneuver. The other answer choices, such as having fishing gear onboard or using non-line fishing methods, do not necessarily mean the vessel is "engaged in fishing" from a rules of the road perspective. The key factor is whether the fishing gear in use impedes the vessel's maneuverability, which would require other vessels to take appropriate action to avoid a collision. Options A, B, and D do not capture this critical aspect of the definition.