Smaller 12x12x36 Live Comstock Beaver Cage Traps work Great for Beaver too.
Developing a clear cut preference for one size Comstock beaver cage trap over another is a tough call, something that is taken from many catches made over time, a slow learning curve. Most often it comes down to situation in the width of the run, which will dictate what size will work best. Simply, he trap should fit the run, no fencing, no crowding.
Having taken 50 and 60 pound beaver in our cage traps with a 12×15 inch opening, I have heard of 60 pounders being caught in 12×12 traps. I am now setting the smaller traps with more confidence. Beaver seem not to refuse the 12×12 as the opening is much larger than a a 10×10 body gripping trap that take large beaver with regularity.
Many, if not most runs, are wide, meaning the 12×18 cages are perfect more often than not. I would not substitute the wide 12×12 trap for a 12×18 in wide runs. However, a wide run can be covered in another way with two 12×12 cages set side by side a couple of inches apart. The 12×12 cage will not only take large beaver, but this side by side setting strategy will provide two chances for catches.
Just yesterday I checked two side by side 12×12 cages and had large beaver in both, a 36 and a 42 pound beaver.