Wreckages can be found while hunting Thalassus during and after Deadliest Catch quest. After initial wreckage is investigated, they can be investigated to reveal the next set of tracks leading to Thalassus. Interacting with the wrong wreckage causes Thalassus to lose interest and after a number of mistakes the progress is reset, although the solution remains the same. Each wreckage can be looted for a choice of items, however each loot can be viewed only once, even if the player didn't take any items.
This information has been compiled as part of the update history project. Some updates may not be included - see here for how to help out!