This is a one year chart comparing the U.S. Natural Gas ETF (NYSE: UNG) to a Gulf Coast natural gas1 royalty trust I own a few shares of, Tidelands Royalty Trust (OTC BB: TIRTZ.OB):
And this is a three month chart comparing them:
It makes sense for the share price of the royalty trust to decline as natural gas prices have declined (the natural gas ETF closely tracks natural gas prices), but I don't know what the explanation is for the recent divergence. It is possible, of course, that the trust's distributions could rise if an increase in production outweighs the drop in natural gas prices, but I don't know of any estimates of future production increases for this trust.
1About 90% of this trust's royalties come from natural gas production, with the balance coming from oil production.