Mirelurk Hunters are a stronger version of Mirelurks in Fallout 3. You'll tend to find them near most irradiated sources of water, caves and underground. They are much stronger and faster than the normal Mirelurk. They also stand around 2 feet taller and have a brown shell which sometimes makes them harder to see in the dark.
The Mirelurk Hunter is about as strong as a Super Mutant Brute. Just like normal Mirelurks, they are very vulnerable to attacks in the face. However, if you attempt to kill a Mirelurk Hunter by shooting it's shell, it will take you about the same time as it would to kill a Deathclaw.