§ Mr. William RossTo ask the Secretary of State for Northern Ireland when the disease in fish known as UDN was first recorded in a Northern Ireland river; what were 291W the peak years of incidence; which rivers were most affected; when the incidence of this disease became so low as not to cause concern over the future of salmon stocks; and what were the principal effects on salmon stocks.
§ Mr. ViggersI assume the hon. Gentleman is referring to UDN (ulcerative dermal necrosis) which was first recorded in a Northern Ireland river in 1966. The peak years of incidence were 1966–68. No information exists to allow an accurate assessment of which rivers were most affected. By the early 1970s the incidence of UDN had become so low as to stop concern over the future of salmon stocks. The principal effect on salmon stocks in Northern Ireland was to reduce the number of adult fish surviving to spawn, thus lowering the amount of ova deposited.