Really, the only way to make this work is for the animals to be adopted or embraced as a ceremonial animal, that can only be killed ritually for special, very occasional ceremonial purposes, or in times of famine and hardship.
It's kind of a long shot, because it's easy meat and it's hard to see why local peoples would bust their ass and engage in backbreaking labour and hunting and fishing, when you could just stick a harpoon in one and eat like a king for a month.
Particularly because they'd provide no useful property or services in life - they don't produce wool, they don't produce harvestable milk, no eggs, no harvestable by-products, they're useless as draft or labour animals. So they're completely worthless alive.
On the other hand, their advantage is that they're low cost. They access a food source that nothing else can access, they're not competing with anything else. They just hang around and eat seaweed and don't really bother anything. They probably don't require a lot of maintenance. So the only expense or trade off to keeping them around is that you forego the benefit of eating them more regularly.
Supposedly they do produce useful milk.
Another option would just be to have them survive until modern times, and have someone domesticate them as an experiment. Like how the Russians domesticated foxes.