How do I bait a Walrus? (Or other large mammal)

I'm having fun playing dwarf fortress (Not that kind of fun. At least, not yet) in a Taiga / Arctic ocean biome, and I notice that every now and again, I get a pack of 2-3 walruses showing up on my map.

This generated a single happy thought: tame walruses. War Walruses, even. I looked up on the Dwarf Fortress wiki on how to capture live animals, and everything pointed to cage traps.

Two questions:

a) My Taiga / Tundra / Ocean map is heavy on the open spaces. Is there any trick to "baiting" my cage traps such that I can increase the likelyhood that a walrus stumbles into it?

b) if cage traps are the only way to capture a live animal, what does the "capture live land animal" task at the butcher's shop actually do?

I don't believe that there is any way of increasing the chances of catching one other than putting more down and putting them in the right places where animals walk.

The "Capture Live Land Animal" task actually captures vermin. It uses an animal trap instead of a cage, but after catching them, you'll have to put the vermin in a cage to release it(via lever) after you tame it via "Tame Small Animal" anyway. They can be made pets, but people don't really like vermin much. I don't think that you can slaughter them either so I'd probably recommend against this.