DULUTH, MN (KDAL) - More lead  changes have taken place in the John Beargrease Sled Dog Marathon.  The top mushers have arrived and are resting at the Devil Track checkpoint Tuesday morning.  First in was Nathan Schroeder of Chisholm, followed by Keith Aili of Ray and in third place is Amanda Vogel also of Ray.  Only 9 mushers remain in the race as Alaska's Zoya DeNure scratched at the Trail Center yesterday.  The marathon is expected to end sometime Wednesday at Billy's Bar in Duluth.