A grey 10m long whale swam into an industrial part of Tokyo Bay in early May, causing much surprise. Only 12 sightings of the mammal have been confirmed around Japan since the 1960s. It is rare for grey whales to be sighted in Japan, much less in the capital's congested waterways a spokesman said. Grey whales travel about 20,000 km during their annual migrations between the sea off the coast of Vietnam to Russia's far eastern Sakhalin Island.