I'm having difficulty imagining enough garter snakes that would noticeably damage a FHM population given the FHM have ample structure for laying their eggs. BUT, trapping up to ten at a pop sounds like alot of snakes. What have you totaled so far in the trap? Either way, an hour of trapping that produces that many snakes is worth doing and I would continue those efforts as the catch rate will diminish as the snake population is reduced. That will be your tell-tale sign that your FHM losses are being positively affected and the sacrificial FHM's for bait will pay off in the long run.

As JM says, keeping the terrestrial growth to a minimum will help along with the lack of rock piles and fallen timber.

Are you in the market for a new dog? (short story - thanks for the trip down memory lane) I had an Airedale Terrier once that was H@11 on snakes. It didn't mater what kind, she would whip them back and forth in her mouth until limp...dead snakes everywhere, lol. As a youth, I would collect snakes and, one time, I had about 20 gathered up in trash cans, buckets, and boxes...Old Maggie got in the garage and upended every container and put every one to rest. That was the end of my snake collecting in the gargage (which made Mom rather happy I might add). A terrier is the only snake predator that I can think of that would not have an impact on your FHM's aside from nature's raptors.

Fish on!,
Noel