Muskrat (Ondatra zibethicus) 2015-12-31 Bombay Hook NWR, DE - I'm not certain, but I think these are probably Muskrat tracks.

These prints were at the second corner of the boardwalk by the channel. They were quite a bit smaller than the ones at the first corner.

...in the BBC David Attenborough wildlife documentary "The Life of Mammals" - plant materials compose about 95% of their diets, but they also eat small animals, such as freshwater mussels, frogs, crayfish, fish, and small turtles.
https://en.wikipedia.org/wiki/Muskrat