Why are vertical stabilizers always at the rear of an airplane?
With sea creatures the dorsal fin acts as a keel providing the actual sideways force during the turn. They remain level while turning.

Planes on the other hand bank to turn where the sideways force is provided by the lift of the wings. 

To provide yaw stability the vertical stabilizer should be as far from the center of mass as possible. They are not in front because that would be unstable as the minor deviation from straight ahead would increase the force into the deviation rather than provide a force to counteract it.