Menace From the Deep (Killer Species #1) by Michael P. Spradlin

unnatural selection

EMMET DOYLE HAS JUST ARRIVED IN FLORIDA CITY AND the Everglades. The impenetrable forest and otherworldly creatures are amazing.
   Things quickly get weird, however. A strange creature was recently found dead in the park, and it's definitely not a native species. Someone engineered this.
   Deep in the swamp, someone has been experimenting to create a new breed of apex predator. And they're about to set them loose. Soon Emmet will find himself face-to-face with the new top of the food chain.