When we trapped them at the hatchery all we used was conibears on their travel trails between the river and the ponds. We were typically about 50/50 otter / beaver. Biggest otter was a big female that went 6’3” nose to tail (!!!).
Don’t know if it is legal where you are, but on my hatchery they typically swam up the tail race into the hatchery proper. I built a home made under water trap out of metal fence panels in a basic hoop net design. That put an end to it rather quickly.
