If i'm right the place you are trapping is cove point and the marsh north of you is hanks marsh roughly 2000 acres all federal wild life refuge and has been closed to trapping for 40 years it's mostly dry in the summer and has very few rats in it any more. I trapped a fair amount of the lake this last winter and caught very few rats even trapped down the Klamath river and only ended up with 205 rats between the two places . In the past those two areas would have produced over 1000 rats. it appears to me the rats have died out . I hope it's short lived but I will know more after this coming season when I can put more effort into trapping.
You are correct. There is some predation on the rats at the farm, mostly raptors and otter. I find huts dug out by otter several times through-out the season. And I have also seen Bald Eagles flying by with rats in their talons a few times. And lose a rat or two each check to those otter. If the price on them keeps improving, I might even trap a few.
The last 2 years, when driving over the large dike abutting Hanks Maarsh, I have seen a dozen huge huts from the road, on the very southern-most edge of Hanks. I can't believe that marsh went dry last year. We had abundant water from all that snow the previous winter, but now that I think of it, the commission opened irrigation to all. This summer will be a different story. I live out by Keno, and we had 1 day all winter that got snow that stuck for 24 hours. About 3" on Christmas day. Gone next day. That was it, but plenty of rain. River has been very high, lately.