toph

This is gonna sound weird, but a salvagers best friend is a bear, a bear can easily handle multiple sharks (can't swipe attack, gotta use the bite) a good level bear usually has good stamina, so all you gotta do is grab a bear, level it in a mix of oxygen and stamina, then drop a bit below the surface, just low enough to agro any sharks in the area. Kill the sharks, then you should be good to dive down without issue, if a shark spawns swim it up a bit, and go back down with a bear until the salvage is done. I would not recommend taking the bear to far down though as its easy to overestimate stamina while swimming and biting, the bear will drown if you aren't careful.