A 73-year-old man was captured on CCTV climbing over a railing and diving from a cruise ship off WA's northwest coast.

The man was holidaying aboard the Sun Princess with his wife earlier this month, and they were en-route to Darwin from Broome.

After an argument with his wife over where to eat dinner, the man disappeared and in the morning the alarm was raised.

An air and sea search failed to locate him.

It has since emerged his movements were caught on CCTV footage which shows that after arguing with his wife, the man climbed over a railing and dived into the water, 12 metres below.

The ABC understands the man had dementia and his death is not being treated as suspicious.