29 C.F.R. § 784.122

Certain other activities performed on a fishing vessel in connection with named operations are, functionally and as a practical matter, directly and necessarily a part of such operations. For example, maintenance work performed by members of the fishing crew during the course of the trip on the fishing boat would necessarily be a part of the fishing operation, since the boat itself is as much a fishing instrument as the fishing rods or nets. Similarly, work required on the vessel to keep in good operating condition any equipment used for processing, canning, or packing the named aquatic products at sea is so necessary to the conduct of such operations that it must be considered a part of them and exempt.