What requirement applies to all vessels engaging in towing operations?

In towing operations, vessels are required to show navigation lights at all times to ensure they are visible to other vessels, particularly during low visibility conditions such as nighttime or fog. This requirement is crucial for enhancing safety on the water, as it allows other mariners to see the towing vessel and any tow it may be connected to. Proper lighting enables other operators to assess the size and nature of the vessel's operation, thereby facilitating safe navigation in crowded or narrow waterways.

The other choices may reflect certain operational best practices or specific circumstances, but they do not represent a universal requirement that applies to all towing scenarios like the obligation to display navigation lights. For instance, having a crew member on the bow is not a standard requirement across all towing operations, and while communication using radio is advisable, it is not mandated in every situation. The necessity to show towing lights, while important in many cases, is specific to when the vessel is actively towing rather than a blanket requirement for all towing scenarios.