Bring the Defias Orders to Renn McGill in the waters off the Dreadmurk Shore.
From the wording of the orders you recovered, it looks like the first priority of the Defias will be to locate and secure whatever cargo they possessed.
SI:7 has had a salvage diver named Renn McGill working out of Theramore for some time. When he heard about the shipwreck, Renn went north to dive near the islands the Defias now occupy.
If we're to beat the Defias to this cargo, we'll need his help. Look for him in the waters northeast of a small island just north of the island you visited earlier.