'Sustainable' international commercial whaling is an oxymoron.
(image courtesy of Wikipedia)
There is no way of creating a 'sustainable' international commercial whaling market in international waters. The IWC quota system called the RMP and the supervision system known as the RMS are advisory only. Any pro-whaling nation can register 'reservations' to them and then set their own quotas or ignore quotas, regardless of sustainability.
Japan is the largest market in the world for seafood, it is also a market that has consistently put profits before sustainability. Japan was recently caught red handed ignoring its own Tuna quotas -
Japan also buys over quota Tuna from other nation members of international commercial supervisory organisations like ICCAT and buys Tuna from countries which refuse to recognise international Tuna quotas.
Japan, Norway and Iceland, the driving force behind attempts to overturn the IWC's international moratorium on commercial whaling already have cynical 'reservations' registered against most of the endangered whale species under CITES, as a result the Icelandic and Japanese whaling fleets are hunting protected whale species this season.