Complex sentence: Efforts to find the wreck of the ship were made by at least four different expeditions, and it was finally discovered in September 2006, at a depth of about 50 metres in the Chukchi Sea.
Split into simpler sentences: Efforts to find the wreck of the ship have been made by at least four different expeditions. The wreck of the ship was finally discovered in September 2006 at a depth of about 50 metres in the Chukchi Sea.