My two cents.
I showed the sonar picture to my father, an old aviator and sailor. After thirty seconds, he handed it back to me and said, “It's just an anchor with the anchor chain, or even part of the davit with it.” It's true that even iron steamers/liners from the 1870s and 1880s were still equipped with huge conventional anchors carried/secured on the outside of the hull... One should have lost his apparatus during a strong gale.
We don't really know the scale of measurement of this sonar image.
Leaving aside Ric's comment on the strength of the central wings section, I'm having trouble recognizing the aft fuselage and the two vertical fins. And where are the engine fairings/mounts?
As far as I'm concerned, you can say anything and everything about this image, it's like seeing a face in a cloud...