The Caribbean monk seal has gone "the way of the dodo" and been officially listed as extinct by the US Government. The Caribbean monk seal is, so far, the only seal species to go extinct due to human causes.
The last time anyone sighted the Caribbean monk seal was in 1952, over 50 years ago, at Seranilla Bank, between Jamaica and the Yucatan Peninsula. In 1967 the USA listed the species as endangered due to human activities.
Unfortunately it seems that the Hawaiian and Mediterranean monk seals will go the same path as the Caribbean monk seal. Their biggest problems is "lack of food sources for young seals, entanglement in marine debris, predation by sharks, and loss of haul-out and pupping beaches due to erosion" and climate change (which is man-made).
The Hawaiian seal population is expected to be around 1200 individuals. But that number is declining at a rate of 4%, every year. It is even worse for the Mediterranean monk seal that only has around 500 individuals.