Rule 35 (d) states:
(d) A vessel engaged in fishing, when at anchor, and a vessel restricted in her ability to maneuver when carrying out her work at anchor, shall instead of the signals prescribed in Rule 35(g) sound the signal prescribed in Rule 35(c).
The answers above show that the fishing boat is actually engaged in fishing, so instead of sounding the anchor alert sound it can sound the fog signal every two minutes. The vessel restricted in its ability to maneuver, however, is ~not~ described as being engaged in her work. If she's not working, she's just another power-driven vessel and should sound fog signals for being at anchor.
(d) A vessel engaged in fishing, when at anchor, and a vessel restricted in her ability to maneuver when carrying out her work at anchor, shall instead of the signals prescribed in Rule 35(g) sound the signal prescribed in Rule 35(c).
The answers above show that the fishing boat is actually engaged in fishing, so instead of sounding the anchor alert sound it can sound the fog signal every two minutes. The vessel restricted in its ability to maneuver, however, is ~not~ described as being engaged in her work. If she's not working, she's just another power-driven vessel and should sound fog signals for being at anchor.