Tolga and Fatin contact you on the radio and demand another meeting - an you fin them near the fishing village waiting for you. They tell you that they need 10 rolls of Duct Tape and Power Cables.
If you have been scrounging all along you should already have these so just turn them into both right now to complete the first part of the side-quest.
Next they want you to obtain a military grade sonar set - the Field HQ is on the nearby bridge. You do not have to run all the way back to find the start of the bridge - you can climb up inside one of the footings but you have to be careful to make each jump successfully as otherwise, well, you will die.
After you climb to the top of the bridge and retrieve the Sonar Unit you radio in only to be told that they don't need it now - and that completes the mission!