There were 3 well defined trails exiting the river where the beavers were girdling a landowner's trees. I am helping the gentleman out and doing it for free. Naturally, I placed 3 drowning sets in front of these trails. I used raw castor in a jar with river water and poured it on the trails. At the water's edge, I used a small amount of Sweetwater Flattail on a twig to center the beavers on the run. The next day I had 2 beavers. I let the traps soak one more night to be sure. The following morning, I found one sprung set. My question is, do I need to be using castor at all on these trails? Should I start introducing castor after a miss?

Well defined trails and I use no castor or lure. You could have a smart one with the sprung trap but that could have been another critter that did that. Smart beaver can be a challenge.

Stick a peeled fresh piece of poplar...3-4 inches behind the trap...they can't refuse that

Also make sure you have plenty of pan tension .

A good way to measure that...is to see if the pan supports a 4 foot long ..2x4 board..set gentle

On the pan. If not ...tighten that pan screw a touch

I don't bait good trails. I Just hang a snare or put a foot holds in a touch off center usually a snare on trails and save my few beaver foothold for caster mound set locations.

May want to try snare or body grips if legal if you now have an educated one. The few times I had a miss It usually toolk a different type of trap to catch it. Had a sprung 300 but caught a beaver a few days later in a 750 on a caster mound set with freshly ripped up tail. Got ya.

OR have a toenail in a #5 and catch one missing toenail in a snare a day or so later.