Firstly, before WW11, whale meat was not part of (and largely isn't now) the Japanese diet. Large scale whaling was established by the Allied occupation forces, as a source of food, when General Douglas MacArthur was the military governor of Japan --- nothing "cultural" or "historic" about it.
Leadsled:
I have found references to ancient and more modern evidence of whaling and dolphin hunting in the Jomon period but no reference to increase of whaling by post war Japan
Cheers
BH