* Climate change, overfishing threaten fishermen on Nile * Fish stocks dwindling while some species have disappeared * Rising temperatures could harm food security, experts warn By Ela Yokes OMDURMAN, Sudan, April 4 (Thomson Reuters Foundation) - A l-Nimeiry Musa Mohammad has spent 25 years fishing on the Nile river in Sudan but he has never been so worried about the future, as catches dwindle and more fishermen seek other sources of income. "I know many people who left the profession because of a lack of fish.