Which type of vessels do not have to comply with the rules regarding traffic separation schemes, to the extent necessary for their work?

The correct choice relates to vessels that require flexibility in navigation due to the nature of their work. Vessels engaged in servicing submarine cables are often involved in specialized operations that necessitate deviating from established traffic separation schemes. These operations are deemed essential for the maintenance and installation of submarine cables, which are crucial for global telecommunications and power transmission.

Therefore, the regulations acknowledge that such work may require exceptions to the standard rules in place for navigational safety, understanding that the nature of this activity can't always conform to conventional traffic patterns. This provision allows for safe operations without compromising ongoing maintenance and utility functions critical to communication infrastructure.

In contrast, the other types of vessels listed, such as regular fishing vessels, luxury yachts, and passenger ferries, are generally expected to follow the rules established for traffic separation schemes since their operations do not necessitate deviations from these rules in the way that servicing submarine cables does.