Another Update:
I created a few stealthy, good sight characters, and was hoping to see how they fared against seal, but I've never really got the hang of stealthy hunting in general, so I ended up in my "well I'm starving, better kill village livestock" cycle. Died being kicked by a sheep one game... but that's another story.
My new current character is an attempt to get good at agriculture but he is fairly quick, has decent eyesight, and is moderately stealthy. I'm on the south coast near the Reemi, and have been seeing a fair number of seals. I've managed to kill 2 without projectiles or traps.
The first one was lucky, saw a seal on the zoomed out map, zoomed in on the near shore, and was placed within 2 spaces of the seals. I ran to close the gap and killed it on the spot.
The second one I saw while walking along the shore. I was about 12 or so spaces away when I saw it, went into stealth mode and got within 6, then ran before it could get to the water. If I was smart I would have taken one more step to get between it and the sea, but rather stood there and hit it with my sickle 6 times. It was prone, but managed to roll itself into the sea. I must have caused some bleeding wounds because I found it 3 days layer floating dead in the area, after running into it several times between.
So, in conclusion, I think there is actually a fairly reasonable way to hunt seals without traps if your character has the right skills, and you aren't desperate enough that you can wait for the odd seal encounter.