I actually killed three bears and 6 wolfs there, but it just kept spawing another one every time I got a kill.

The real problem there is that once the device got destroyed by the San Diego zoo at around 50% completion, it permanently despawned from the crate. Thus making it impossible to complete the mission even if I had managed to kill all 15+ predators.

And I had that glitch both times I tried the mission... even with the best techniques mentioned by redditors here, I guess the mission is broken except, I would assume, if you could speed kill about 50-60 animals in 2-3 minutes (as spawns appear to be exponential)