Louise,

The answer is "no" and "it depends."

First the "it depends" part. WWI U-boats did at times take prisoners, generally by removing them from lifeboats. Those most likely to be taken prisoner were ship captains (masters/skippers). The degree to which this happened varied -- that's the "it depends" element. It depended upon the tactical siuation obviously, the size of the U-boat, the U-boat commander involved, and the command to which the U-boat was attached, among other factors.

UC 18 was a Flanders-based UCII-type minepaying submarine. UCIIs were relatively small, limiting their ability to take prisoners. Flanders-based boats in general were much less likely to take prisoners than those assigned to other commands. I would not have expected UC 18 to take any prisoners from the Netherton.

There is in fact nothing to suggest that any of the crew of the Netherton was taken prisoner. The official publication "British Vessels Lost at Sea 1914-18" provides crew casualties figures, including crew taken prisoner. It states that there were no casualties or crew taken prisoner from this sinking.

Best wishes,
Michael