What is the theme in Ice Hunt by James Rollins?

Survival of a species is a central theme. The Grendels are a remarkable species. Thought to be the evolutionary link between the whale and land mammal, they are a cross between the two. An intelligent species, they use sonar to communicate and locate much like whales, but they have feet with claws and are able to survive and travel out of the water as well. In fact, in this instance, the ice cave they use as a nest is all above the water and they use a series of ice tunnels and caves to traverse it.